ETM Experimental and Therapeutic Medicine 1792-0981 1792-1015 D.A. Spandidos ETM-27-5-12478 10.3892/etm.2024.12478 Review Role and targeting of the AGC kinase family in pulmonary fibrosis (Review) MeiChao ChenTao HuangXiangfei XiongChenlu ChenShibiao LiYong Department of Anesthesiology, The First Affiliated Hospital, Jiangxi Medical College, Nanchang University, Nanchang, Jiangxi 330006, P.R. China Correspondence to: Professor Shibiao Chen or Professor Yong Li, Department of Anesthesiology, The First Affiliated Hospital, Jiangxi Medical College, Nanchang University, 17 Yongwai Street, Nanchang, Jiangxi 330006, P.R. China chenlaoshi1111@163.com liyong@ncu.edu.cn 05 2024 08 03 2024 27 5 190 28 04 2023 26 01 2024 Copyright © 2024, Spandidos Publications 2024

Pulmonary fibrosis (PF) is a progressive and irreversible pulmonary disease with a high mortality rate and limited treatment options. The cAMP-dependent protein kinase A, cGMP-dependent protein kinase G and phospholipid-dependent protein kinase C, collectively known as AGC kinases, are evolutionarily conserved protein kinases that are widely distributed among eukaryotes. AGC kinases serve a crucial role in a variety of cellular functions and pathological processes, including cancer, diabetes, inflammation and viral infections, where they have been implicated the pathogenesis of PF. The present review summarizes the evidence for the involvement of specific AGC kinases in the pathogenesis of PF, and provides a theoretical basis for the development of targeted AGC kinase small molecule inhibitors or targeted drugs, offering more effective treatment options and strategies for patients with PF.

 pulmonary fibrosis cAMP-dependent protein kinase A cGMP-dependent protein kinase G phospholipid-dependent protein kinase C extracellular matrix epithelial cell fibroblasts Funding: The present study was supported by grants from the National Natural Science Foundation of China (grant nos. 82060023 and 82160133) and the Jiangxi Provincial Natural Science Foundation (grant nos. 20202ACBL206015, 20224BAB206007 and 20212ACB216005). 1. Introduction

Pulmonary fibrosis (PF) is a respiratory disease that is characterized by scarring in the lungs and subsequent breathing difficulties (1). There are various types of PF including asbestosis, hypersensitivity pneumonitis and idiopathic pulmonary fibrosis (IPF), with IPF being one of the most common and severe forms (2). IPF is an interstitial lung disease of unknown etiology that is chronic, progressive, and irreversible (3). It is distinguished by epithelial cell activation and injury, fibroblast proliferation and differentiation, extracellular matrix (ECM) deposition, irreversible destruction of the alveolar structure and respiratory insufficiency (Fig. 1) (4). IPF primarily occurs among the middle-aged and elderly populations, where it is limited to the lungs (5,6). The treatment of IPF typically involves a combination of medications, pulmonary rehabilitation and, in some cases, lung transplantation (7). IPF is a chronic and progressive disease, and existing treatments, including antifibrotic medications, aim to slow down the progression rather than cure the condition (7). However, the antifibrotic medications may have side effects, and not all individuals with IPF can tolerate these drugs (8). The causes and pathogenesis of IPF remain unclear and the effects conferred by currently available therapeutic methods are limited (9,10). The survival rate after IPF diagnosis is typically only 2-5 years, where the prognosis of which is even worse compared with that of several types of cancer including uterine, breast and colon cancer (5).

Epithelial cell dysfunction and senescence has emerged as a central component of the IPF pathophysiology (11,12). The alveolar epithelium consists of alveolar epithelial type 1 (AT1) and alveolar epithelial type 2 cells (AT2). The alveolar surface is mostly covered by AT1 cells, whose thin squamous morphology and intimate contact with the adjacent capillary plexus permit efficient gas exchange (13). Although loss of AT1 cells is considered to be a cardinal feature of the IPF histology, accumulating evidence has revealed AT2 cells to also serve an important role in IPF (14,15). This is in part due to its function in alveolar niche homeostasis through the production of pulmonary surfactants and as a progenitor cell for both self-renewal and transdifferentiation into AT1 cells if needed (13). In particular, single-cell RNA sequencing has previously identified a cell population expressing both AT2 (SOX4, SOX9, COL1A1 and FN1) and AT1 (COL1A1, FN1 and SCGB1A1) markers in IPF lungs, suggesting a subset of epithelial cells transitioning between the AT1 and AT2 phenotype (16).

In eukaryotic cells, a substantial proportion of signal transduction activity is facilitated by protein kinases, which is achieved through phosphorylation of target substrates (17,18). This process serves pivotal roles in the regulation of a wide variety of cellular functions, including proliferation, differentiation, metabolism and programmed cell death (19,20). In humans, protein kinases can be categorized into nine groups based on the evolutionary relationships of their catalytic domains (17,18,21). One such group is one consisting of cAMP-dependent protein kinase A, cGMP-dependent protein kinase G and phospholipid-dependent protein kinase C (AGC), collectively known as AGC kinases (21).

AGC kinases form a highly conserved group of kinases that are ubiquitously distributed across different orders of eukaryotic organisms (21). Members of the AGC kinases group have been reported to regulate different cellular processes, where their targets may have therapeutic implications for various human diseases, including but not limited to cancer, diabetes, obesity, immunological disorders, inflammation, neurological disorders, viral infections and muscular dystrophies (21-24). Therefore, targeting members of the AGC kinases may prove to be a potential method of treatment for PF.

The present review summarizes the reported significant effects of AGC kinases on the pathological procession of PF, before discussing their potential as molecular targets for the treatment of this disease. In addition, focus will be placed on the role of different families of AGC kinases in PF.

 2. AGC kinases

The AGC kinase group is comprised of 63 serine/threonine protein kinases that are evolutionarily related. This group includes the protein kinase G and protein kinase C families of kinases, Akt/protein kinase B, Aurora kinases, ribosomal protein S6 kinases and the phosphoinositide-dependent kinases (17,22,24). In addition, the majority of AGC kinases each have multiple isoforms and splice variants, increasing the complexity of this family of kinases (25).

AGC kinases typically exhibit a conserved fold that is characterized by a catalytic domain consisting of a small N-terminal lobe and a large C-terminal lobe (21). The predominant secondary structure of the large C-terminal lobe is α-helical, whereas the small N-terminal lobe is comprised of a single helix (α-C) and a 5-stranded β-sheet (22). An ATP-binding site is located between the two lobes (21,26), where the bound ATP serves as the phosphate donor during phosphorylation (25). The activation loop originating from an Aspartate-Phenylalanine-Glycine motif is also situated amidst the large and the small lobe (21). In addition. the majority of AGC kinases contain a conserved catalytic core with a C-terminal hydrophobic motif (HM) sequence (21). This HM sequence is known to bind to a co-evolved hydrophobic site in the small lobe of the catalytic core, which is referred to as the 3-phosphoinositide-dependent protein kinase-1-interacting fragment (PIF)-pocket (Fig. 2) (27,28). According to a previous study, the PIF-pocket is proposed to be a central and common on-off switch in the AGC kinases (22). Apart from the conserved catalytic domain, the AGC kinases group contains various functional domains. The AGC kinases can be classified into 14 families and 21 subfamilies based on homology outside the catalytic domain (17,25).

AGC kinases serve a crucial role in regulating a multitude of cellular functions, including but not limited to cell cycle progression, cellular differentiation, cell survival and apoptosis (21). In both animals and yeast, AGC kinases have been documented to serve as key mediators that are capable of transducing signaling cascades initiated by secondary messengers through substrate phosphorylation (29,30). In plants, AGC kinases have been demonstrated to serve indispensable roles in diverse cellular and developmental processes including growth, immunity, cell death and defense responses (31-33).

 3. AGC kinases in PF <sec> <title>Pyruvate dehydrogenase kinase 1 (PDK1)

PDK1 is a serine/threonine kinase that was initially discovered in previous studies on insulin-activated Akt signaling in the presence of phosphatidylinositol-3,4,5-triphosphate (PIP3) (34-36). PDK1 is a conserved protein kinase that is expressed in eukaryotes (37). PDK1 is mainly located in the cytoplasm, but under certain conditions it can be induced to translocate into the nucleus (38). PDK1 was originally considered to be a regulator of glycolysis in the cytoplasm (39-41). Subsequent studies have revealed that PDK1 can regulate a number of physiological processes, such as blood vessel formation, metabolism and development (42,43). In addition, the pathological processes of Alzheimer's disease (44), diabetes (45) and cancer (46,47) have all been reported to be caused at least in part by PDK1 activity (39).

Previous studies have revealed that PDK1 serves a role in the regulation of PF. The PDK1 gene was previously shown to be a direct target gene of hypoxia-inducible factor-1 (HIF-1) (48,49). Glycolytic metabolism, which is mediated by PDK-1, serves a crucial role in the progression of PF (50-52). Goodwin et al (53) previously reported that hypoxia markedly enhanced transforming growth factor-β (TGF-β)-induced myofibroblast differentiation in fibrotic lesions via HIF-1α. However, overexpression of PDK1 was sufficient in activating glycolysis and potentiate myofibroblast differentiation regardless of the existence of HIF-1α. Additionally, bleomycin (BLM)-induced PF can be significantly attenuated by using dichloroacetate, a potent PDK inhibitor (54,55). Yang et al (56) revealed that PDK1 knockdown can attenuate PF by inhibiting the NF-κB/p65 signaling pathway. Mannan-binding lectin (MBL) can interact with and ubiquitinate PDK1 to inhibit epithelial-mesenchymal transition (EMT) in PF by attenuating store-operated calcium entry (SOCE) signaling (57). However, the specific mechanism of PDK1 in IPF remains unclear.

 Rho-associated coiled-coil-forming protein kinase (ROCK)

ROCK is a downstream target protein of Rho and has been implicated in a wide range of cell functions, such as proliferation, migration, adhesion, apoptosis and differentiation (58-60). ROCK has two isoforms, namely ROCK-I and ROCK-II, which regulate cytoskeletal reorganization by phosphorylating myosin phosphatase to increase the phosphorylation level of myosin light chain (61). In addition to brain and muscle tissues, the expression of ROCK-I is widespread, whilst ROCK-II expression tends to be limited to the brain and muscle, especially in the smooth muscle (62). However, the functional differences between ROCK-I and ROCK-II remain unclear (59).

ROCK-II mRNA expression has been previously revealed to be increased in a murine model of lung fibrosis induced by BLM (59). The Rho/ROCK signaling pathway can be inhibited to prevent fibrosis by decreasing the levels of inflammatory cells (macrophages, neutrophils and lymphocytes) and cytokine (TGF-β1, connective tissue growth factor (CTGF) and plasminogen activator inhibitor (PAI)-1 levels (59,63). Shimizu et al (64) demonstrated that the expression and activity of ROCK-II was increased in several types of lung cells in patients with IPF, including bronchial epithelial cells, airway smooth muscle cells, vascular smooth muscle cells and fibroblasts (64). The RhoA/ROCK-I signaling pathway has also been demonstrated to promote the migration of lung fibroblasts and synthesis of collagen by myofibroblasts, both of which can exacerbate PF (65). Rho/ROCK inhibitors, such as Fasudil, have been shown to attenuate BLM-induced lung fibrosis by suppressing the recruitment of inflammatory cells such as neutrophils and reducing the production of TGF-β1, CTGF, α-smooth muscle actin (α-SMA) and PAI-1 in BLM-induced mouse lungs (63). Recently, compound 9b, a novel selective inhibitor of ROCK-II, has demonstrated marked anti-PF effects by suppressing the expression of α-SMA and collagen I in BLM-induced IPF mice model (66). Notably, dual pharmacological inhibition of ROCK-I and -II was found to counteract TGF-β-induced PF in an organoid assay, which included freshly isolated EpCAM+ mouse lung cells co-cultured with human lung fibroblasts (67). However, it should be emphasized that although the main role of ROCK in PF has been established, the precise regulatory mechanisms mediated by Rho/ROCK signaling require further clarification.

 Large tumor suppressor 1/2 (LATS1/2)

LATS1 and 2 are important components of the kinase cascades in the Hippo signal pathway in mammalian cells (68-70). A number of studies have demonstrated that LATS2 and its downstream signaling pathway have a vital impact on the proliferation, migration, differentiation and immunomodulation of mesenchymal stem cells (MSCs) (71,72). Dong and Li (71) previously revealed that LATS2-underexpressing bone marrow-derived MSCs (transfected with LATS2-interfering lentivirus vector) can repair the alveolar epithelium damaged by lipopolysaccharide in a mouse model of acute lung injury (ALI).

Lung injury has been reported to trigger the fibrotic process (73). Previous studies have demonstrated that MSCs can reduce collagen fiber deposition and alleviate early-stage PF in mice with ALI (74,75). Dong and Li (71) revealed that this effect is amplified in bone marrow-derived mesenchymal stem cells with low expression levels of LATS2 (due to transfection with LATS2-interfering lentivirus vector). However, further studies are required to investigate the specific mechanisms of LATS in PF.

 AKT

AKT, also known as PKB, has three isoforms in mammals, namely AKT1, AKT2 and AKT3. It can regulate numerous cellular processes, such as cell survival, proliferation, differentiation and intermediary metabolism (76-81). Specifically, it has been previously revealed that both AKT1 and AKT2 can modulate the migration and invasion of cancer cells. AKT1 can stimulate prostate cancer cell motility, whereas AKT2 inhibits motility and migration in breast cancer and ovarian cancer cells (82,83). Since AKT3 is primarily expressed in the brain tissue and has only been reported to serve a role in neuronal development (84), research on the role of AKT in PF has mainly concentrated on AKT1 and AKT2(81).

Previous studies have demonstrated that TGF-β1 can regulate the activation of AKT in myofibroblasts and that inhibiting the function of AKT can alleviate TGF-β1-induced PF (85,86). It has been found that AKT1 and AKT2 can mediate significant roles in regulating the function of alveolar macrophages in IPF (87,88). Specifically, AKT1 can promote macrophage mitochondrial reactive oxygen species (ROS) and mitophagy, as well as increase TGF-β1 expression, resulting in the development of fibrosis (88). In addition, the pro-fibrotic cytokine IL-13, can be upregulated by AKT1 in macrophages in PF (89). Nie et al (87) revealed that AKT2 phosphorylation is upregulated in the tissues of patients with PF. AKT2 deficiency protects against BLM-induced PF and inflammation (87). In conclusion, AKT may serve an important role in the development of IPF, suggesting that it can be a potential molecular target for its therapeutic intervention.

 Protein kinase C (PKC)

PKC is a type of phospholipid-dependent serine/threonine kinase for which 12 isozymes have been identified (90). PKCs are classified into three subfamilies, based on structural and activation characteristics: conventional or classic PKCs (cPKCs: α, βI, βII and γ), novel or non-classic PKCs (nPKCs: δ, ε, η and θ), and atypical PKCs (aPKC: ζ, ι and λ) (91). PKC isozymes participate in signal transduction by either directly or indirectly activating or inactivating target proteins through phosphorylation (92). PKC has been documented to mediate various cellular processes, including proliferation, migration, apoptosis, adhesion and differentiation (93-96).

The role of PKC-δ in IPF remains controversial, despite its reported involvement in the progression of PF (97). PKC-δ has been reported to inhibit NF-κB signaling by enhancing the activity and stability of A20, which is an endogenous negative regulator of NF-κB (97). In addition, the deficiency of PKC-δ has been reported to increase the expression of proinflammatory cytokines to exacerbate inflammation and PF induced by BLM (97), suggesting that PKC-δ may serve a protective role in IPF. Previous studies have demonstrated that the inhibitor of PKC-δ rottlerin can downregulate the expression of type I and type III collagen gene, and suppress the type I collagen production in cultured dermal fibroblasts derived from patients with systemic sclerosis (98). Additionally, Song et al (99) revealed that thrombin induces EMT and collagen I secretion by activating protease-activated receptor (PAR-1), PKC (α/β, δ and ε) and ERK1/2 in A549 cells. A549 is an adenocarcinomic human alveolar basal epithelial cell line, that is widely used as a model of alveolar epithelial-like behavior in IPF study (100). Therefore, targeting PAR-1 or specific PKC isoforms (α, β, δ and ε) may halt the fibrotic process in human IPF by preventing thrombin-induced EMT. Results reported by the aforementioned studies suggest that PKC-δ may promote IPF. However, the possible link between PKC and IPF require further studies.

 Ribosome protein S6 kinase (RPS6K)

RPS6Ks can be divided into two subfamilies, p90 ribosomal S6 kinase (RSK) and p70 ribosomal S6 kinase (p70S6K). The p70S6K subfamily has two members of the p70S6K (S6K1 and S6K2), whilst the RSK subfamily has four members (RSK1-4) (101,102). RSK is activated by the ERK signaling pathway. p70S6K is activated through a complex network of signaling molecules, and mTOR serine/threonine kinase is necessary for its full activation (103). These kinases are involved in various signaling pathways and can regulate multiple cellular processes, such as cell proliferation, differentiation, growth, transformation and apoptosis (104-108).

Madala et al (109) previously revealed an increase in S6 phosphorylation in the airway and alveolar epithelium and in the mesenchyme of advanced subpleural fibrotic regions of TGF-α-induced PF mice. The specific targeted inhibition of the S6K with the small molecule inhibitor LY-2584702 attenuates TGF-α and platelet-derived growth factor-β-induced proliferation of pulmonary fibroblasts (109). In another study, Han et al (110) revealed that rapamycin, an mTOR inhibitor, can attenuate BLM-induced PF and EMT by decreasing S6K- and TGF-β1-induced Smad2/3 phosphorylation. In addition, S6K was also found to enhance proliferation and fibroblast-to-myofibroblast transition in human embryonic lung fibroblasts (111). Kim et al (112) revealed that inhibition of RSK suppressed TGF-β1-induced ECM accumulation and EMT in lung epithelial cells and fibroblasts. These findings suggest that RPS6K may also have a role in the development of IPF. However, the specific mechanism underlying IPF progression requires further elucidation.

 4. Conclusions

The AGC kinases form a widely conserved family of protein kinases that have been implicated in various pathologies, including cancer, metabolic disorders, cardiovascular disease, immunological disorders and neurological disorders. Accumulating evidence has shown that AGC kinases can exert important roles in IPF through distinct mechanistic pathways (Table I). Several inhibitors of AGC kinases such as RSK-inhibitor peptide (112), dichloroacetate (53), BX795 and BX912(113) have been found to attenuate PF. However, additional research is required to fully comprehend the contribution of AGC kinases towards IPF. Identification of AGC kinases with the potential to serve as therapeutic targets of IPF may facilitate the discovery of novel drugs for IPF treatment.

At present, to the best of our knowledge, only a small number of AGC kinases have been found to be involved in regulating the pathological process of PF. To further explore the key role of AGC kinases comprehensively in the pathogenesis of PF, more functions of AGC kinases in PF need to be explored. As single-cell sequencing and spatial proteomics technology advance, the distinct functions mediated by AGC kinase in various cell types during different stages of PF will be elucidated (114-116). In addition, continuous advancements in organoid technology are expected to facilitate studies into the microenvironment of lung tissues in the pathological process of PF in the future, where the role of AGC kinases should also be investigated. Understanding the specific substrates and associated signaling pathways by AGC kinases in the regulation of PF will also be a focus of future attention. Based on the results and findings of existing studies, it would be of benefit to screen small molecule inhibitors or targeted drugs for AGC kinase and conduct relevant clinical trials, providing more effective treatment options and strategies for patients with IPF.

 Acknowledgements

Not applicable.

 Availability of data and materials

Not applicable.

 Authors' contribution

YL conceived the study and revised the manuscript. CM prepared the figures and wrote the manuscript. TC, XH and CX participated in the writing of the manuscript. SC reviewed the manuscript. All authors have read and approved the final manuscript. Data authentication is not applicable.

 Ethics approval and consent to participate

Not applicable.

 Patient consent for publication

Not applicable.

 Competing interests

The authors declare that they have no competing interests.

 References NoblePWBarkauskasCEJiangDPulmonary fibrosis: Patterns and perpetratorsJ Clin Invest1222756276220122285088610.1172/JCI60323 KreuterMLadnerUMCostabelUJonigkDHeusselCPThe diagnosis and treatment of pulmonary fibrosisDtsch Arztebl Int11815216220213353111510.3238/arztebl.m2021.0018 RicheldiLCollardHRJonesMGIdiopathic pulmonary fibrosisLancet3891941195220172836505610.1016/S0140-6736(17)30866-8 GüntherAKorfeiMMahavadiPvon der BeckDRuppertCMarkartPUnravelling the progressive pathophysiology of idiopathic pulmonary fibrosisEur Respir Rev2115216020122265408810.1183/09059180.00001012 RaghuGCollardHREganJJMartinezFJBehrJBrownKKColbyTVCordierJFFlahertyKRLaskyJAAn official ATS/ERS/JRS/ALAT statement: Idiopathic pulmonary fibrosis: Evidence-based guidelines for diagnosis and managementAm J Respir Crit Care Med18378882420112147106610.1164/rccm.2009-040GL LedererDJMartinezFJIdiopathic pulmonary fibrosisN Engl J Med3781811182320182974238010.1056/NEJMra1705751 AbuserewaSTDuffRBeckerGTreatment of idiopathic pulmonary fibrosisCureus13e1536020213423979210.7759/cureus.15360 KhorYHAntifibrotic therapy for idiopathic pulmonary fibrosis: Combining real world and clinical trials for totality of evidenceChest1601589159120213474384010.1016/j.chest.2021.07.033 DesaiOWinklerJMinasyanMHerzogELThe role of immune and inflammatory cells in idiopathic pulmonary fibrosisFront Med (Lausanne)54320182961622010.3389/fmed.2018.00043 FujimotoHKobayashiTAzumaAIdiopathic pulmonary fibrosis: Treatment and prognosisClin Med Insights Circ Respir Pulm Med9 (Suppl 1)S179S18520162798044510.4137/CCRPM.S23321 SelmanMPardoAThe leading role of epithelial cells in the pathogenesis of idiopathic pulmonary fibrosisCell Signal6610948220203176017210.1016/j.cellsig.2019.109482 TuMWeiTJiaYWangYWuJMolecular mechanisms of alveolar epithelial cell senescence and idiopathic pulmonary fibrosis: A narrative reviewJ Thorac Dis1518620320233679413410.21037/jtd-22-886 KatzenJBeersMFContributions of alveolar epithelial cell quality control to pulmonary fibrosisJ Clin Invest1305088509920203287081710.1172/JCI139519 ParimonTYaoCStrippBRNoblePWChenPAlveolar epithelial type II cells as drivers of lung fibrosis in idiopathic pulmonary fibrosisInt J Mol Sci21226920203221823810.3390/ijms21072269 ZhuWTanCZhangJAlveolar epithelial type 2 cell dysfunction in idiopathic pulmonary fibrosisLung20053954720223613613610.1007/s00408-022-00571-w HabermannACGutierrezAJBuiLTYahnSLWintersNICalviCLPeterLChungMITaylorCJJetterCSingle-cell RNA sequencing reveals profibrotic roles of distinct epithelial and mesenchymal lineages in pulmonary fibrosisSci Adv6eaba197220203283259810.1126/sciadv.aba1972 ManningGWhyteDBMartinezRHunterTSudarsanamSThe protein kinase complement of the human genomeScience2981912193420021247124310.1126/science.1075762 RoskoskiR JrA historical overview of protein kinases and their targeted small molecule inhibitorsPharmacol Res10012320152620788810.1016/j.phrs.2015.07.010 DeribeYLPawsonTDikicIPost-translational modifications in signal integrationNat Struct Mol Biol1766667220102049556310.1038/nsmb.1842 AttwoodMMFabbroDSokolovAVKnappSSchiöthHBTrends in kinase drug discovery: Targets, indications and inhibitor designNat Rev Drug Discov2083986120213435425510.1038/s41573-021-00252-y ArencibiaJMPastor-FloresDBauerAFSchulzeJOBiondiRMAGC protein kinases: From structural mechanism of regulation to allosteric drug development for the treatment of human diseasesBiochim Biophys Acta18341302132120132352429310.1016/j.bbapap.2013.03.010 LerouxAESchulzeJOBiondiRMAGC kinases, mechanisms of regulation and innovative drug developmentSemin Cancer Biol4811720182859165710.1016/j.semcancer.2017.05.011 RathNOlsonMFRho-associated kinases in tumorigenesis: Re-considering ROCK inhibition for cancer therapyEMBO Rep1390090820122296475810.1038/embor.2012.127 TurnhamREScottJDProtein kinase A catalytic subunit isoform PRKACA; history, function and physiologyGene57710110820162668771110.1016/j.gene.2015.11.052 PearceLRKomanderDAlessiDRThe nuts and bolts of AGC protein kinasesNat Rev Mol Cell Biol1192220102002718410.1038/nrm2822 ZhengJKnightonDRten EyckLFKarlssonRXuongNTaylorSSSowadskiJMCrystal structure of the catalytic subunit of cAMP-dependent protein kinase complexed with MgATP and peptide inhibitorBiochemistry32215421611993844315710.1021/bi00060a005 BiondiRMCheungPCCasamayorADeakMCurrieRAAlessiDRIdentification of a pocket in the PDK1 kinase domain that interacts with PIF and the C-terminal residues of PKAEMBO J1997998820001069893910.1093/emboj/19.5.979 BiondiRMKomanderDThomasCCLizcanoJMDeakMAlessiDRvan AaltenDMHigh resolution crystal structure of the human PDK1 catalytic domain defines the regulatory phosphopeptide docking siteEMBO J214219422820021216962410.1093/emboj/cdf437 ZhangYMcCormickSAGCVIII kinases: At the crossroads of cellular signalingTrends Plant Sci1468969520091981867410.1016/j.tplants.2009.09.006 SobkoASystems biology of AGC kinases in fungiSci STKE2006re920061697147710.1126/stke.3522006re9 Lanassa BassukasAEXiaoYSchwechheimerCPhosphorylation control of PIN auxin transportersCurr Opin Plant Biol6510214620223497422910.1016/j.pbi.2021.102146 JiangYLiuXZhouMYangJKeSLiYGenome-wide identification of the AGC protein kinase gene family related to photosynthesis in rice (Oryza sativa)Int J Mol Sci231255720223629340710.3390/ijms232012557 GlancMVan GelderenKHoermayerLTanSNaramotoSZhangXDomjanDVčelařováLHauschildRJohnsonAAGC kinases and MAB4/MEL proteins maintain PIN polarity by limiting lateral diffusion in plant cellsCurr Biol3119181930.e520213370571810.1016/j.cub.2021.02.028 WickKLLiuFA new molecular target of insulin action: Regulating the pivotal PDK1Curr Drug Targets Immune Endocr Metabol Disord120922120011247728710.2174/1568008013341082 AlessiDRJamesSRDownesCPHolmesABGaffneyPRReeseCBCohenPCharacterization of a 3-phosphoinositide-dependent protein kinase which phosphorylates and activates protein kinase BalphaCurr Biol72612691997909431410.1016/s0960-9822(06)00122-9 StokoeDStephensLRCopelandTGaffneyPRReeseCBPainterGFHolmesABMcCormickFHawkinsPTDual role of phosphatidylinositol-3,4,5-trisphosphate in the activation of protein kinase BScience2775675701997922800710.1126/science.277.5325.567 DittrichACNDevarenneTPPerspectives in PDK1 evolution: Insights from photosynthetic and non-photosynthetic organismsPlant Signal Behav764264920122258069810.4161/psb.20038 ScheidMPParsonsMWoodgettJRPhosphoinositide-dependent phosphorylation of PDK1 regulates nuclear translocationMol Cell Biol252347236320051574382910.1128/MCB.25.6.2347-2363.2005 GagliardiPAdi BlasioLPrimoLPDK1: A signaling hub for cell migration and tumor invasionBiochim Biophys Acta185617818820152623847110.1016/j.bbcan.2015.07.003 CohenPAlessiDRCrossDAPDK1, one of the missing links in insulin signal transduction?FEBS Lett4103101997924711210.1016/s0014-5793(97)00490-0 ZhouYGuoYRanMShanWGranchiCGiovannettiEMinutoloFPetersGJTamKYCombined inhibition of pyruvate dehydrogenase kinase 1 and lactate dehydrogenase a induces metabolic and signaling reprogramming and enhances lung adenocarcinoma cell killingCancer Lett57721642520233780516310.1016/j.canlet.2023.216425 FengQDiRTaoFChangZLuSFanWShanCLiXYangZPDK1 regulates vascular remodeling and promotes epithelial-mesenchymal transition in cardiac developmentMol Cell Biol303711372120102045780910.1128/MCB.00420-10 LawlorMAMoraAAshbyPRWilliamsMRMurray-TaitVMaloneLPrescottARLucocqJMAlessiDREssential role of PDK1 in regulating cell size and development in miceEMBO J213728373820021211058510.1093/emboj/cdf387 PietriMDakowskiCHannaouiSAlleaume-ButauxAHernandez-RappJRagagninAMouillet-RichardSHaikSBaillyYPeyrinJMPDK1 decreases TACE-mediated α-secretase activity and promotes disease progression in prion and Alzheimer's diseasesNat Med191124113120132395571410.1038/nm.3302 HashimotoNKidoYUchidaTAsaharaSShigeyamaYMatsudaTTakedaATsuchihashiDNishizawaAOgawaWAblation of PDK1 in pancreatic beta cells induces diabetes as a result of loss of beta cell massNat Genet3858959320061664202310.1038/ng1774 ChoucairKAGuérardKPEjdelmanJChevalierSYoshimotoMScarlataEFazliLSircarKSquireJABrimoFThe 16p13.3 (PDPK1) genomic gain in prostate cancer: A potential role in disease progressionTransl Oncol545346020122340173910.1593/tlo.12286 MaurerMSuTSaalLHKoujakSHopkinsBDBarkleyCRWuJNandulaSDuttaBXieY3-Phosphoinositide-dependent kinase 1 potentiates upstream lesions on the phosphatidylinositol 3-kinase pathway in breast carcinomaCancer Res696299630620091960258810.1158/0008-5472.CAN-09-0820 KimJWTchernyshyovISemenzaGLDangCVHIF-1-mediated expression of pyruvate dehydrogenase kinase: A metabolic switch required for cellular adaptation to hypoxiaCell Metab317718520061651740510.1016/j.cmet.2006.02.002 PapandreouICairnsRAFontanaLLimALDenkoNCHIF-1 mediates adaptation to hypoxia by actively downregulating mitochondrial oxygen consumptionCell Metab318719720061651740610.1016/j.cmet.2006.01.012 LiJZhaiXSunXCaoSYuanQWangJMetabolic reprogramming of pulmonary fibrosisFront Pharmacol13103189020223645222910.3389/fphar.2022.1031890 HamanakaRBMutluGMMetabolic requirements of pulmonary fibrosis: Role of fibroblast metabolismFEBS J2886331635220213339320410.1111/febs.15693 HendersonJO'ReillySThe emerging role of metabolism in fibrosisTrends Endocrinol Metab3263965320213402469510.1016/j.tem.2021.05.003 GoodwinJChoiHHsiehMHNeugentMLAhnJMHayengaHNSinghPKShackelfordDBLeeIKShulaevVTargeting hypoxia-inducible factor-1α/pyruvate dehydrogenase kinase 1 axis by dichloroacetate suppresses bleomycin-induced pulmonary fibrosisAm J Respir Cell Mol Biol5821623120182891506510.1165/rcmb.2016-0186OC StacpoolePWReview of the pharmacologic and therapeutic effects of diisopropylammonium dichloroacetate (DIPA)J Clin Pharmacol J New Drugs928229119694902026 StacpoolePWKurtzTLHanZLangaeeTRole of dichloroacetate in the treatment of genetic mitochondrial diseasesAdv Drug Deliv Rev601478148720081864762610.1016/j.addr.2008.02.014 YangKLiBChenJKnockdown of phosphoinositide-dependent kinase 1 (PDK1) inhibits fibrosis and inflammation in lipopolysaccharide-induced acute lung injury rat model by attenuating NF-κB/p65 pathway activationAnn Transl Med9167120213498818010.21037/atm-21-5476 LiuYXieXWangPLuoJChenYXuQZhouJLuXZhaoJChenZZuoDMannan-binding lectin reduces epithelial-mesenchymal transition in pulmonary fibrosis via inactivating the store-operated calcium entry machineryJ Innate Immun15374920233567170510.1159/000524693 LoirandGGuérinPPacaudPRho kinases in cardiovascular physiology and pathophysiologyCirc Res9832233420061648462810.1161/01.RES.0000201960.04223.3c ShimizuYDobashiKIizukaKHorieTSuzukiKTukagoshiHNakazawaTNakazatoYMoriMContribution of small GTPase Rho and its target protein rock in a murine model of lung fibrosisAm J Respir Crit Care Med16321021720011120864810.1164/ajrccm.163.1.2001089 BarceloJSamainRSanz-MorenoVPreclinical to clinical utility of ROCK inhibitors in cancerTrends Cancer925026320233659973310.1016/j.trecan.2022.12.001 ShimokawaHTakeshitaARho-kinase is an important therapeutic target in cardiovascular medicineArterioscler Thromb Vasc Biol251767177520051600274110.1161/01.ATV.0000176193.83629.c8 KnipeRSTagerAMLiaoJKThe Rho kinases: Critical mediators of multiple profibrotic processes and rational targets for new therapies for pulmonary fibrosisPharmacol Rev6710311720152539550510.1124/pr.114.009381 JiangCHuangHLiuJWangYLuZXuZFasudil, a Rho-kinase inhibitor, attenuates bleomycin-induced pulmonary fibrosis in miceInt J Mol Sci138293830720122294270310.3390/ijms13078293 ShimizuYDobashiKSanoTYamadaMROCK activation in lung of idiopathic pulmonary fibrosis with oxidative stressInt J Immunopathol Pharmacol27374420142467467710.1177/039463201402700106 GhatakSHascallVCMarkwaldRRFeghali-BostwickCArtlettCMGoozMBogatkevichGSAtanelishviliISilverRMWoodJTransforming growth factor β1 (TGFβ1)-induced CD44V6-NOX4 signaling in pathogenesis of idiopathic pulmonary fibrosisJ Biol Chem292104901051920172838956110.1074/jbc.M116.752469 FuSWenYPengBTangMShiMLiuJYangYSiWGuoYLiXDiscovery of indoline-based derivatives as effective ROCK2 inhibitors for the potential new treatment of idiopathic pulmonary fibrosisBioorg Chem13710653920233716381110.1016/j.bioorg.2023.106539 WuXVerschutVWoestMENg-BlichfeldtJPMatiasAVillettiGAccettaAFacchinettiFGosensRKistemakerLEMRho-kinase 1/2 inhibition prevents transforming growth factor-β-induced effects on pulmonary remodeling and repairFront Pharmacol1160950920213355181010.3389/fphar.2020.609509 HongAWMengZGuanKLThe Hippo pathway in intestinal regeneration and diseaseNat Rev Gastroenterol Hepatol1332433720162714748910.1038/nrgastro.2016.59 WuZGuanKLHippo signaling in embryogenesis and developmentTrends Biochem Sci46516320213292862910.1016/j.tibs.2020.08.008 LandryNMRattanSGFilomenoKLMeierTWMeierSCForanSJMeierCFKoleiniNFandrichRRKardamiESKI activates the Hippo pathway via LIMD1 to inhibit cardiac fibroblast activationBasic Res Cardiol1162520213384783510.1007/s00395-021-00865-9 DongLLiLLats2-underexpressing bone marrow-derived mesenchymal stem cells ameliorate LPS-induced acute lung injury in miceMediators Inflamm2019485143120193177250310.1155/2019/4851431 AntebiBWalkerKP IIIMohammadipoorARodriguezLAMontgomeryRKBatchinskyAICancioLCThe effect of acute respiratory distress syndrome on bone marrow-derived mesenchymal stem cellsStem Cell Res Ther925120183025770210.1186/s13287-018-0981-3 KuwanoKMiyazakiHHagimotoNKawasakiMFujitaMKunitakeRKanekoYHaraNThe involvement of Fas-Fas ligand pathway in fibrosing lung diseasesAm J Respir Cell Mol Biol2053601999987091710.1165/ajrcmb.20.1.2941 CaiSXLiuARChenSHeHLChenQHXuJYPanCYangYGuoFMHuangYZThe orphan receptor tyrosine kinase ROR2 facilitates MSCs to repair lung injury in ARDS animal modelCell Transplant251561157420162653117510.3727/096368915X689776 HanJLuXZouLXuXQiuHE-prostanoid 2 receptor overexpression promotes mesenchymal stem cell attenuated lung injuryHum Gene Ther2762163020162715885510.1089/hum.2016.003 Fernández-HernandoCAckahEYuJSuárezYMurataTIwakiriYPrendergastJMiaoRQBirnbaumMJSessaWCLoss of Akt1 leads to severe atherosclerosis and occlusive coronary artery diseaseCell Metab644645720071805431410.1016/j.cmet.2007.10.007 IliopoulosDPolytarchouCHatziapostolouMKottakisFMaroulakouIGStruhlKTsichlisPNMicroRNAs differentially regulated by Akt isoforms control EMT and stem cell renewal in cancer cellsSci Signal2ra6220091982582710.1126/scisignal.2000356 RevathideviSMunirajanAKAkt in cancer: Mediator and moreSemin Cancer Biol59809120193117385610.1016/j.semcancer.2019.06.002 RissoGBlausteinMPozziBMammiPSrebrowAAkt/PKB: One kinase, many modificationsBiochem J46820321420152599783210.1042/BJ20150041 TokerAYoeli-LernerMAkt signaling and cancer: Surviving but not moving onCancer Res663963396620061661871110.1158/0008-5472.CAN-06-0743 WangJHuKCaiXYangBHeQWangJWengQTargeting PI3K/AKT signaling for treatment of idiopathic pulmonary fibrosisActa Pharm Sin B12183220223512737010.1016/j.apsb.2021.07.023 VirtakoivuRPellinenTRantalaJKPeräläMIvaskaJDistinct roles of AKT isoforms in regulating β1-integrin activity, migration, and invasion in prostate cancerMol Biol Cell233357336920122280962810.1091/mbc.E12-03-0213 ArboledaMJLyonsJFKabbinavarFFBrayMRSnowBEAyalaRDaninoMKarlanBYSlamonDJOverexpression of AKT2/protein kinase Bbeta leads to up-regulation of beta1 integrins, increased invasion, and metastasis of human breast and ovarian cancer cellsCancer Res63196206200312517798 BaekSTCopelandBYunEJKwonSKGuemez-GamboaASchafferAEKimSKangHCSongSMathernGWGleesonJGAn AKT3-FOXG1-reelin network underlies defective migration in human focal malformations of cortical developmentNat Med211445145420152652397110.1038/nm.3982 KangHRLeeCGHomerRJEliasJASemaphorin 7A plays a critical role in TGF-beta1-induced pulmonary fibrosisJ Exp Med2041083109320071748551010.1084/jem.20061273 HorowitzJCRogersDSSharmaVVittalRWhiteESCuiZThannickalVJCombinatorial activation of FAK and AKT by transforming growth factor-beta1 confers an anoikis-resistant phenotype to myofibroblastsCell Signal1976177120071711326410.1016/j.cellsig.2006.10.001 NieYSunLWuYYangYWangJHeHHuYChangYLiangQZhuJAKT2 regulates pulmonary inflammation and fibrosis via modulating macrophage activationJ Immunol1984470448020172845543310.4049/jimmunol.1601503 Larson-CaseyJLDeshaneJSRyanAJThannickalVJCarterABMacrophage Akt1 kinase-mediated mitophagy modulates apoptosis resistance and pulmonary fibrosisImmunity4458259620162692110810.1016/j.immuni.2016.01.001 NieYHuYYuKZhangDShiYLiYSunLQianFAkt1 regulates pulmonary fibrosis via modulating IL-13 expression in macrophagesInnate Immun2545146120193129985810.1177/1753425919861774 KazanietzMGCookeMProtein kinase C signaling ‘in’ and ‘to’ the nucleus: Master kinases in transcriptional regulation. J Biol Chem: 105692, 2024 (Epub ahead of print). SilnitskySRubinSJSZerihunMQvitNAn update on protein kinases as therapeutic targets-part I: Protein kinase C activation and its role in cancer and cardiovascular diseasesInt J Mol Sci241760020233813942810.3390/ijms242417600 KangJHToitaRKimCWKatayamaYProtein kinase C (PKC) isozyme-specific substrates and their designBiotechnol Adv301662167220122284193310.1016/j.biotechadv.2012.07.004 AbeMKKarthaSKarpovaAYLiJLiuPTKuoWLHershensonMBHydrogen peroxide activates extracellular signal-regulated kinase via protein kinase C, Raf-1, and MEK1Am J Respir Cell Mol Biol185625691998953394510.1165/ajrcmb.18.4.2958 BarmanSAPotassium channels modulate canine pulmonary vasoreactivity to protein kinase C activationAm J Physiol277L558L56519991048446310.1152/ajplung.1999.277.3.L558 DasMStenmarkKRRuffLJDempseyECSelected isozymes of PKC contribute to augmented growth of fetal and neonatal bovine PA adventitial fibroblastsAm J Physiol273L1276L12841997943558410.1152/ajplung.1997.273.6.L1276 HarringtonEOLöfflerJNelsonPRKentKCSimonsMWareJAEnhancement of migration by protein kinase Calpha and inhibition of proliferation and cell cycle progression by protein kinase Cdelta in capillary endothelial cellsJ Biol Chem272739073971997905443910.1074/jbc.272.11.7390 WangJSunLNieYDuanSZhangTWangWYeRDHouSQianFProtein kinase C δ (PKCδ) attenuates bleomycin induced pulmonary fibrosis via inhibiting NF-κB signaling pathwayFront Physiol1136720203239086910.3389/fphys.2020.00367 JimenezSAGaidarovaSSaittaBSandorfiNHerrichDJRosenbloomJCKucichUAbramsWRRosenbloomJRole of protein kinase C-delta in the regulation of collagen gene expression in scleroderma fibroblastsJ Clin Invest1081395140320011169658510.1172/JCI12347 SongJSKangCMParkCKYoonHKThrombin induces epithelial-mesenchymal transition via PAR-1, PKC, and ERK1/2 pathways in A549 cellsExp Lung Res3933634820132391945010.3109/01902148.2013.820809 BarosovaHMeldrumKKarakocakBBBalogSDoakSHPetri-FinkACliftMJDRothen-RutishauserBInter-laboratory variability of A549 epithelial cells grown under submerged and air-liquid interface conditionsToxicol In Vitro7510517820213390584010.1016/j.tiv.2021.105178 McMullenJRShioiTZhangLTarnavskiOSherwoodMCDorfmanALLongnusSPendeMMartinKABlenisJDeletion of ribosomal S6 kinases does not attenuate pathological, physiological, or insulin-like growth factor 1 receptor-phosphoinositide 3-kinase-induced cardiac hypertrophyMol Cell Biol246231624020041522642610.1128/MCB.24.14.6231-6240.2004 LudwikKALanniganDARibosomal S6 kinase (RSK) modulators: A patent reviewExpert Opin Ther Pat261061107820162741099510.1080/13543776.2016.1212839 ShimaHPendeMChenYFumagalliSThomasGKozmaSCDisruption of the p70(s6k)/p85(s6k) gene reveals a small mouse phenotype and a new functional S6 kinaseEMBO J17664966591998982260810.1093/emboj/17.22.6649 MagnusonBEkimBFingarDCRegulation and function of ribosomal protein S6 kinase (S6K) within mTOR signalling networksBiochem J44112120122216843610.1042/BJ20110892 PullenNDennisPBAndjelkovicMDufnerAKozmaSCHemmingsBAThomasGPhosphorylation and activation of p70s6k by PDK1Science2797077101998944547610.1126/science.279.5351.707 RouxPPShahbazianDVuHHolzMKCohenMSTauntonJSonenbergNBlenisJRAS/ERK signaling promotes site-specific ribosomal protein S6 phosphorylation via RSK and stimulates cap-dependent translationJ Biol Chem282140561406420071736070410.1074/jbc.M700906200 SoaresHPNiYKisfalviKSinnett-SmithJRozengurtEDifferent patterns of Akt and ERK feedback activation in response to rapamycin, active-site mTOR inhibitors and metformin in pancreatic cancer cellsPLoS One8e5728920132343736210.1371/journal.pone.0057289 FrödinMGammeltoftSRole and regulation of 90 kDa ribosomal S6 kinase (RSK) in signal transductionMol Cell Endocrinol151657719991041132110.1016/s0303-7207(99)00061-1 MadalaSKThomasGEdukullaRDavidsonCSchmidtSSchehrAHardieWDp70 ribosomal S6 kinase regulates subpleural fibrosis following transforming growth factor-α expression in the lungAm J Physiol Lung Cell Mol Physiol310L175L18620162656690310.1152/ajplung.00063.2015 HanQLinLZhaoBWangNLiuXInhibition of mTOR ameliorates bleomycin-induced pulmonary fibrosis by regulating epithelial-mesenchymal transitionBiochem Biophys Res Commun50083984520182970450410.1016/j.bbrc.2018.04.148 ZouWZhangXZhaoMZhouQHuXCellular proliferation and differentiation induced by single-layer molybdenum disulfide and mediation mechanisms of proteins via the Akt-mTOR-p70S6K signaling pathwayNanotoxicology1178179320172871480410.1080/17435390.2017.1357213 KimSHanJHKimSLeeHKimJRLimJHWooCHp90RSK inhibition ameliorates TGF-β1 signaling and pulmonary fibrosis by inhibiting smad3 transcriptional activityCell Physiol Biochem5419521020203208340610.33594/000000214 JiaSAgarwalMYangJHorowitzJCWhiteESKimKKDiscoidin domain receptor 2 signaling regulates fibroblast apoptosis through PDK1/AktAm J Respir Cell Mol Biol5929530520182965251810.1165/rcmb.2017-0419OC WangLLiZWanRPanXLiBZhaoHYangJZhaoWWangSWangQSingle-cell RNA sequencing provides new insights into therapeutic roles of thyroid hormone in idiopathic pulmonary fibrosisAm J Respir Cell Mol Biol6945646920233740227410.1165/rcmb.2023-0080OC AdamsTSSchuppJCPoliSAyaubEANeumarkNAhangariFChuSGRabyBADeIuliisGJanuszykMSingle-cell RNA-seq reveals ectopic and aberrant lung-resident cell populations in idiopathic pulmonary fibrosisSci Adv6eaba198320203283259910.1126/sciadv.aba1983 YangLGilbertsenASmithKXiaHHigginsLGuerreroCHenkeCAProteomic analysis of the IPF mesenchymal progenitor cell nuclear proteome identifies abnormalities in key nodal proteins that underlie their fibrogenic phenotypeProteomics22e220001820223563352410.1002/pmic.202200018

Characteristic manifestations of IPF. (A) Injury of alveolar epithelial cells. (B) Fibroblasts are activated, and proliferate and differentiate into myofibroblasts. (C) Deposition of ECM and irreversible destruction of alveolar structure. ECM, extracellular matrix; IPF, idiopathic pulmonary fibrosis.

Conserved catalytic domain and specific features of most AGC kinases. HM, hydrophobic motif; PIF, PDK-interacting fragment.

Mechanisms of AGC kinases in IPF.

First author(s), year AGC kinases Isoforms Mechanisms (Refs.)
Yang et al, 2021 PDK1   NF-κB/p65 pathway (56)
Goodwin et al, 2018     Hypoxia-inducible factor-1a/3-phosphoinositide-dependent protein kinase-1-mediated glycolytic reprogramming (53)
Jiang et al, 2012 ROCK   Rho/ROCK signaling pathway (63)
Shimizu et al, 2014     Rho/ROCK signaling pathway (64)
Dong and Li, 2019 Large tumor suppressor   Hippo signaling pathway (71)
Wang et al, 2022 AKT   PI3K/AKT signaling pathway (81)
Nie et al, 2019   AKT1 Modulating IL-13 expression in macrophages (89)
Nie et al, 2017   AKT2 AKT2/Forkhead box O3a signaling pathway (87)
Song et al, 2013 PKC   Protease-activated receptor-1/PKC/ERK pathways (99)
Wang et al, 2020   PKC-δ NF-κB/A20 signaling (97)
Kim et al, 2020 p90 ribosomal S6 kinase   TGF-β1/smad3 signaling (112)
Madala et al, 2016 S6K   S6K signaling (109)

ROCK, Rho-associated coiled-coil-forming protein kinase; PKC, protein kinase C; S6K, p70 ribosomal S6 kinase.