Downregulation of NOB1 suppresses the proliferation and tumor growth of non-small cell lung cancer in vitro and in vivo

Retraction in: /10.3892/or.2020.7483

  • Authors:
    • Yang Li
    • Chengyuan Ma
    • Ming Qian
    • Zhongmei Wen
    • Hongyu Jing
    • Donghua Qian
  • View Affiliations

  • Published online on: January 21, 2014     https://doi.org/10.3892/or.2014.2991
  • Pages: 1271-1276
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Abstract

Non-small cell lung cancer (NSCLC) is a lethal disease due to the absence of effective diagnostic biomarkers and therapeutic targets. Therefore, novel molecular targets are critically needed to formulate new approaches for this devastating disease. In the present study, using quantitive real-time PCR and immunohistochemistry. we initially found that expression of the ribosome assembly factor NIN/RPN12 binding protein (NOB1) was elevated in the majority of NSCLC tissues when compared to that in the normal lung tissue counterparts, and its expression level was correlated with key pathological characteristics including tumor differentiation, stage and metastasis. Then, the recombinant lentiviral shRNA expression vector carrying NOB1 was constructed and infected into the human NSCLC A549 cell line. Cell proliferation, cell apoptosis, cell cycle distribution and colony formation ability in A549 cells were assessed following downregulation of NOB1 by siRNA. In addition, tumor growth ability in nude mice was evaluated to define the function of NOB1 in cell transformation and tumorigenesis. It was found that downregulation of NOB1 expression using the RNA silencing approach in A549 tumor cells significantly suppressed the proliferation and colony formation ability, and induced tumor apoptosis in vitro. Tumor growth was also suppressed in vivo. These data suggest that NOB1 is an important regulator of the tumorigenic properties of human NSCLC and may be used as a new promising diagnostic biomarker and a potential anticancer therapeutic target for NSCLC.

Introduction

Non-small cell lung cancer (NSCLC) is the leading cause of cancer-related mortality worldwide, with less than 15% of patients surviving beyond 5 years due to the difficulty of early diagnosis and the absence of effective treatment methods (1,2). Cytotoxic chemotherapy remains the therapeutic foundation for treatment in both the adjuvant and metastatic settings (35). Although much effort has been made in the advancement of chemotherapeutic regimens in NSCLC, these therapies are toxic and are almost never curative in the case of metastatic disease. Thus, it is crucial to develop novel molecular diagnostic markers and therapeutic targets for the treatment of NSCLC.

The NIN1/RPN12 binding protein 1 homologue (NOB1) is a subunit of the 26 S proteasome and is composed of nine exons and eight introns, and is located on chromosome 16q22.1 (6). NOB1 protein, an evolutionarily conserved protein, comprises a PilT N terminus (PIN) domain and a C terminal zinc ribbon domain (7,8) and is expressed mainly in the liver, lung and spleen (6). The PIN domain was postulated as the enzymatic domain of Nob1 since cells expressing the mutant PIN failed to cleave the 20S pre-rRNA, strengthening the notion that NOB1 is the long-sought D-site endonuclease (9,10). It has been found that genetic depletion of Nob1 strongly suppresses the processing of the 20S pre-rRNA to the mature 18S rRNA, producing markedly high levels of the 20S pre-RNA with novel degradation intermediates (11). These studies showed that NOB1 plays a crucial role in protease function and RNA metabolism.

Recently, increased NOB1 expression has been reported in breast and ovarian cancer, and hepatocellular carcinoma (1214). Lu et al (13) found that NOB1 is an important regulator of the tumorigenic properties of human hepatocellular carcinoma and may be used as a candidate therapeutic target in human hepatocellular carcinoma. Lin et al (14) found that downregulation of NOB1 expression by siRNA suppresses cell proliferation and survival and may be used as a therapeutic marker in ovarian cancer. Huang et al (12) showed that NOB1 plays an essential role in breast cancer cell proliferation, and its gene expression may be a therapeutic target. These results suggest that NOB1 may be involved in the progression of various types of tumors, although little information concerning the expression of NOB1 and its role in other tumors is available. To the best of our knowledge, the correlation between the expression of the NOB1 gene and the pathological characteristics of NSCLC has not been determined, and whether NOB1 affects tumor cell proliferation or tumor growth in NSCLC remains unclear. The aims of the present study were, therefore, to investigate the expression of NOB1 in NSCLC, and to analyze its association with the occurrence and development of NSCLC. In addition, the effect of the downregulation of NOB1 by siRNA on NSCLC tumor growth in vitro and in vivo was investigated.

Materials and methods

Cell lines and human samples

The human non-small cell lung cancer A549 cell line was purchased from the Cell Bank of the Type Culture Collection of the Chinese Academy of Sciences, Shanghai Institute of Cell Biology, Chinese Academy of Sciences. A549 cells were cultured in RPMI-1640 medium (Invitrogen, Carlsbad, CA, USA) supplemented with 10% fetal bovine serum (FBS; Biochrom AG Biotechnologie, Berlin, Germany) at 37°C in a humidified atmosphere containing 5% CO2. Fresh-frozen primary NSCLC tissues and their paired normal samples were obtained from patients undergoing surgical resection at Shanghai Chest Hospital (Shanghai, China) from May 2009 to June 2012 after consent was obtained from the patients. None of the patients received any prior radiochemotherapy. Clinicopathological information was collected from the clinical data of the NSCLC patients (Table I).

Table I

Correlation of NOB1 overexpression with clinicopathological features of the NSCLC cases.

Table I

Correlation of NOB1 overexpression with clinicopathological features of the NSCLC cases.

NOB1 expression

Clinical factorsPositiveNegativeP-value
Age (years)
 <55 (n=29)2180.751
 ≥55 (n=31)274
Gender
 Male (n=36)3060.764
 Female (n=24)186
Smoking history
 No (n=35)2870.543
 Yes (n=25)205
Metastasis
 None (n=28)1810<0.01
 N1–N2 (n=26)1511
 M1 (n=6)60
Tumor differentiation
 Well (n=10)28<0.01
 Moderate (n=20)182
 Poor (n=30)282
Clinical stage
 I–II (n=35)2411<0.05
 III–IV (n=25)241
Immunohistochemistry

To detect the expression and localization of NOB1 protein in the NSCLC tissues, immunohistochemistry was performed using an SP reagent kit (Tiangen Biotech, Co., Ltd., Beijing, China) according to the manufacturer’s instructions. Immunoreactivity was measured semi-quantitatively using a scale from 0 to 3, where a score of 0 represents no immunostaining, 1 represents <25% cell reactivity, 2 represents 25–50% cell reactivity, 3 represents >50% cell reactivity. Values of 0 and 1 were considered to indicate negative staining, and 2 and 3 were considered to indicate positive staining. Five cases with discordant results were re-evaluated to obtain agreement.

Construction and transfection of pGCSIL-GFP-shNOB1

To inhibit the expression of Nob1, two short hairpin RNAs (shRNAs) targeting the Nob1 transcript were designed. The synthesized oligonucleotides which contained a specific target sequence, a loop, the reverse complement of the target sequence, a stop codon for the U6 promoter and two sticky ends were cloned into the pGCSIL-GFP lentiviral vector according to the manufacturer’s instructions (Shanghai GenePharma Co., Ltd., Shanghai, China). The target sequence in the oligonucleotide for suppressing siRNA1 was AAGGTT AAGGTGAGCTCATCG (sense) and the siRNA2 sequence was GATTGAAGAATGCCGGATA (sense). The negative control siRNA sequence was AATTCTCCGAACGTGTCA CGT (sense). The resulting constructs allowed for the transient and stable expression of the siRNA. Lentiviruses carrying the NOB1 siRNAs and the negative control siRNA were infected into A549 lung cancer cells as previously described (13).

Cell proliferation assay

Cell proliferation was assessed using an MTT cell proliferation kit (Roche Applied Science, Indianapolis, IN, USA) according to the manufacturer’s instructions. In brief, the cells were seeded on 96-well microplates at a density of 1.0×104 cells/well. At 1–6 days and at post-transfection with NOB1 siRNAs (optional), the cells were incubated with 20 μl of MTT labeling reagent for 4 h, followed by the addition of 200 μl solubilization solution into each well. The plates were kept in a dark room overnight, and the OD of each sample was measured at a 490 nm test wavelength with an ELISA multi-well spectrophotometer (Molecular Devices, Sunnyvale, CA, USA).

Analysis of apoptosis

A549 cells were cultured in 6-well plates in RPMI-1640 with 10% FBS medium and were treated with different siRNAs for 24, 48 and 72 h. The coverslips were washed three times with phosphate-buffered saline (PBS), and single-cell suspensions were fixed in 1% PBS. Cells were stained with 100 μg/ml acridine orange (AO) and 100 μg/ml ethidium bromide (EB) for 1 min. Then cells were observed under a fluorescence microscope. At least 200 cells were counted, and the percentage of apoptotic cells was determined. Triplicates were performed for all experiments, and experiments were performed on five occasions.

Cell colony formation assay

Cell suspensions containing siRNAs (1×104 diluted in 0.33% low-melting agarose) were overlaid on the bottom of a 0.5% agar layer (3 ml) in a 60-mm dish. Cells were incubated at 37°C for 2 weeks, and the medium was replaced every 3 days. After washing twice with PBS, the colonies were fixed with ice methanol for 30 min and stained with Giemsa for 10 min. Then, the visible colonies were counted.

Analysis of the cell cycle distribution

The cell cycle distribution of the cells transfected with the siRNAs or NC was analyzed using FACScan flow cytometry. In brief, 5×105 cells were seeded in a 6-cm dish overnight. The cells were collected, washed with PBS, and fixed with cold 70% ethanol. The fixed cells were then treated with 50 μg/ml DNase-free RNase and incubated for 30 min at 37°C. Propidium iodide (20 μg/ml; Sigma) was added directly to the cell suspension, and a total of 10,000 fixed cells were analyzed by FACScan (Becton-Dickinson).

Tumor xenograft assay

All animal experiments were performed in accordance with the institutional guidelines, following a protocol approved by the Ethics Committees of the Disease Model Research Center, The First Hospital of Jilin University. Female BALB mice, approximately 6–8 weeks of age, were maintained under specific pathogen-free conditions and were provided with food and water ad libitum. All of the animals were fed with a normal pellet diet one week prior to the experimentation. In vitro cultured A549 cells were injected s.c. into the right supra scapula region of the mice. The tumor volume was calculated using the formula: Volume = length × width2/2. When tumors grew to an average volume of 75 mm3, the mice were randomly divided into siRNA1, siRNA2 and NC groups (n=10 in each group) and treated by administration of siRNA1, siRNA2 or NC plus PBS in a total volume of 20 μl (10 μl virus plus 10 μl PBS) one time each week for 21 days, respectively. When control mice started to succumb to their tumors, the mice in all treatment groups were euthanized. After the mice had been sacrificed, the tumors were removed and directly embedded in an optimal cutting temperature (OCT) compound in a deep freezer at −80°C.

Real-time quantitative PCR

Total RNA was isolated from the A549 cell line and NSCLC tissues using TRIzol reagent (Invitrogen) according to the manufacturer’s instructions. RNA was reverse-transcribed into cDNA using a Primescript™ RT reagent kit according to the manufacturer’s instructions (Takara, Shiga, Japan). Real-time quantitative polymerase chain reaction (PCR) was performed with the SYBR-Green fluorescent dye method, and a Rotor-Gene 3000 real-time PCR apparatus. The primer sequences were as follows: NOB1 forward, 5′-ATCTGCCCTACAAGCCTAAAC-3′ and reverse antisense, 5′-TCCTCCTCCTCCTCCTCAC-3′; β-actin forward, 5′-GATCATTGCTCCTCCTGAGC-3′ and β-actin reverse, 5′-ACTCCTGCTTGCTGATCCAC-3′. The PCR conditions were as follows: a pre-denaturing step at 95°C for 2 min, followed by 40 cycles of denaturation at 95°C for 10 sec, annealing/extension at 58°C for 20 sec. The amplification specificity was checked by melting curve analysis. The 2−ΔΔCT method was used to calculate the relative abundance of target gene expression generated by Rotor-Gene Real-Time analysis software 6.1.81. For each cDNA, the target gene mRNA level was normalized to that of the β-actin mRNA level. The experiments were performed three times.

Western blot analysis

Cultured cells were washed twice with PBS and lysed in radioimmune precipitation assay buffer for 30 min on ice. Cell lysates were clarified by centrifugation (10,000 × g, 15 min), and protein concentrations were determined using the Bradford reagent (Sigma). Lysates were separated on 8 or 15% SDS-PAG; proteins were transferred to an Immobilon membrane (Millipore, Bedford, MA, USA) immunoblotted with specific primary antibodies and incubated with the corresponding horseradish peroxidase-conjugated secondary antibody. The other primary antibodies used in the western blot analysis were as follows: antibodies against NOB1, p21, cyclin D1, cyclin D3 (Santa Cruz, Biotechnology, Santa Cruz, CA, USA); p53 (Sigma-Aldrich, St. Louis, MO, USA); secondary Abs used for immunodetection were as follows: HRP-conjugated goat anti-mouse IgG and goat anti-rabbit IgG (Amersham Biosciences, Uppsala, Sweden). All immunoblots were visualized by enhanced chemiluminescence (Pierce).

Statistical analysis

All data are expressed as means ± SEM. Statistical analysis between two samples was performed using the Student’s t-test. Statistical comparison of more than two groups was performed using one-way ANOVA followed by a Tukey post hoc test. Pearson’s correlation coefficients were used to determine whether two prognosis related factors were correlated to each other over all cases. The software SPSS 16.0 for Windows was used for statistical analyses, and results were considered significant when P-values were <0.05 or <0.01.

Results

NOB1 is upregulated in NSCLC tissues and correlates with the clinical features of the NSCLC patients

To identify the potential roles of NOB1 in the development and progression of NSCLC, we assessed its expression level by real-time polymerase chain reaction (PCR) in 60 pairs of matched lung tissue samples. Expression levels of NOB1 were significantly higher in the NSCLC tissue samples when compared with the levels in their normal lung tissue counterparts (Fig. 1A). Furthermore, elevated levels of NOB1 protein were found in the NSCLC tissues when compared with the levels in the paired normal tissues from the same patients as shown by immunohistochemical staining (Fig. 1B).

Further analysis revealed that the upregulation of NOB1 in NSCLC samples was inversely correlated with differentiation of the tumors (P<0.01) and was positively correlated with both tumor metastasis and tumor TNM stage (P<0.01; Table I) as determined by immunohistochemistry. No correlations were noted between NOB1 protein levels and smoking history, patient age or gender. These data suggest that NOB1 expression is correlated with advanced NSCLC.

Infection of A549 cells with NOB1 siRNAs

The lentiviruses carrying the NOB1 siRNAs or negative control siRNA were infected into A549 cells. To determine the effect of RNAi on the endogenous expression of NOB1, the mRNA and protein levels of NOB1 were analyzed using real-time RT-PCR and western blotting, respectively. Our data showed that two independent target sequences siRNA1 and siRNA2 markedly decreased the expression of NOB1 when compared with the control sequence (Fig. 2).

Silencing of NOB1 reduces proliferation, colony formation ability and induction of cell apoptosis and induces cell cycle arrest in NSCLC A549 cells

Using these two siRNAs, we examined the effects of NOB1 silencing on tumor cell growth in vitro. The anti-proliferative effect of NOB1 silencing on A549 cells was examined using MTT assays. The silencing of NOB1 significantly inhibited the proliferation of A549 cells when compared with that of the control cells (scrambled siRNA) (Fig. 3A). Conversely, silencing of NOB1 significantly increased the rate of apoptosis of the A549 tumor cells in a time-dependent manner, when compared with this rate in the control cells as determined using AO staining assay (Fig. 3B). Furthermore, the effect of the silencing of NOB1 on lung cancer cell colony formation ability was assessed. As shown in Fig. 3C, silencing of NOB1 reduced the colony number in the tumor cells. To further study the mechanism of the growth inhibition of NOB1, the cell cycle status was determined by DNA flow cytometric analysis. When the NOB1 expression was decreased, there was an increase in the relative number of cells in the G0/G1 phase from 48 to ~66% (Fig. 3D), which was markedly higher than that in the control cells. Together, these data indicate that NOB1 plays an important regulatory role in tumor cell growth and progression of NSCLC.

Silencing of NOB1 suppresses tumor growth in vivo

To investigate the effects of NOB1 on tumor growth and metastasis in a nude mouse model, we conducted a xenograft assay by administering the control (si-scrambled) and NOB1-silenced tumor cells into mice and comparing the growth rate of the solid tumors. We found that the tumor growth rate after NOB1 silencing was significantly slower for NOB1 tumor cells compared with the control cells (Fig. 4). These results indicate that suppression of NOB1 expression in NSCLC tumor cells markedly suppresses their tumorigenicity in mice.

Preliminary mechanisms involved in the regulation of the cell cycle by NOB1

To clarify the molecular mechanisms involved in the inhibition of tumor cell proliferation and cell cycle arrest due to the downregulation of NOB1, in the present study, we focused on the effects of NOB1 silencing on the activation of proteins cyclin D1, cyclin D3 and p21, which participate in the main cell cycle As shown in Fig. 5, silencing of NOB1 significantly inhibited cyclin D1 and cyclin D3 expression and increased p21 expression in the tumor cells, which implies that NOB1 may be a crucial factor in lung cancer cell proliferation and cell cycle progression.

Discussion

Since the identification of the NOB1 protein (6), increased NOB1 expression has been reported in ovarian, colon, breast, thyroid and hepatocellular carcinomas (1216) and human leukaemia (17). However, these studies did not focus on NOB1 expression in NSCLC patients. To the best of our knowledge, in the present study, we initially found that NOB1 was elevated in the majority of NSCLC tissues when compared to the level in the normal lung tissues, and its expression level was correlated with key pathological characteristics including tumor differentiation, stage and metastasis. No correlations were noted between NOB1 protein levels and smoking history, patient age or gender. In addition, our findings also showed that silencing of NOB1 resulted in the inhibition of proliferation of A549 cells in vitro and suppression of solid tumor growth in vivo. These results provide evidence that NOB1 is required for tumor growth and that it may be a diagnostic marker in NSCLC.

Genetic depletion of NOB1 was found to strongly suppress the processing of the 20S pre-rRNA to the mature 18S rRNA, producing markedly high levels of the 20S pre-RNA with novel degradation intermediates (11), the effect corrects rRNA synthesis and affects cell cycle regulation (18,19), since it is necessary for the synthesis of rRNA for the cell cycle process (20,21). In addition, NOB1 protein plays a major role in the proteasome by forming a complex between the 19S regulatory particle of the 26S proteasome where the latter catalyzes the protein degradation through the ubiquitin proteasome pathway for cell cycle progression (2224). These studies imply that NOB1 affects cell cycle progression.

To investigate the exact mechanism, we analyzed expression of the cell cycle-related proteins following silencing of NOB1 by western blot analysis. The p21 protein is a widely accepted cell cycle regulator, as a cyclin dependent kinase (CDK) inhibitor, and a negative regulator in the G1/S transition (25). The p21 protein has been shown to inhibit cyclin A or cyclin E bound to CDK2 (26) and CDK4 bound to cyclin D1 or cyclin D2 (27). It can also interact with CDK 4/6 complexes thereby inhibiting kinase activity and cell proliferation (28,29). In the present study, we observed that compared to the control cells transfected with the empty vectors, p21 expression was markedly increased after silencing of NOB1. Whereas, cyclin D1 or cyclin D3 expression decreased after silencing. These data showed that NOB1 downregulation affects p21, cyclin D3 and cyclin D1 to reduce lung carcinoma cell proliferation.

In summary, to the best of our knowledge, this is the first full-scale report concerning the association of NOB1 and non-small cell lung cancer. Our data indicate that silencing of NOB1 expression is not only closely related to in vitro cell proliferation and the cell cycle, but is also linked to non-small cell lung cancer growth in vivo. Our analysis of clinical studies also demonstrated that NOB1 is an independent prognostic marker that may serve as a useful clinical biomarker for predicting tumor progression in NSCLC.

Acknowledgements

The present study was supported by grants from the National Natural Science Foundation of Jilin (Project no. 83657488).

References

1 

Jemal A, Siegel R, Xu J and Ward E: Cancer statistics, 2010. CA Cancer J Clin. 60:277–300. 2010. View Article : Google Scholar

2 

Reungwetwattana T, Weroha SJ and Molina JR: Oncogenic pathways, molecularly targeted therapies, and highlighted clinical trials in non-small-cell lung cancer (NSCLC). Clin Lung Cancer. 13:252–266. 2012. View Article : Google Scholar : PubMed/NCBI

3 

Schiller JH: Small cell lung cancer: defining a role for emerging platinum drugs. Oncology. 63:105–114. 2002. View Article : Google Scholar : PubMed/NCBI

4 

Stinchcombe TE and Socinski MA: Treatment paradigms for advanced stage non-small cell lung cancer in the era of multiple lines of therapy. J Thorac Oncol. 4:243–250. 2009. View Article : Google Scholar : PubMed/NCBI

5 

Ramalingam S and Belani CP: Recent advances in targeted therapy for non-small cell lung cancer. Expert Opin Ther Targets. 11:245–257. 2007. View Article : Google Scholar : PubMed/NCBI

6 

Zhang Y, Ni J, Zhou G, et al: Cloning, expression and characterization of the human NOB1 gene. Mol Biol Rep. 32:185–189. 2005. View Article : Google Scholar : PubMed/NCBI

7 

Makarova KS, Aravind L, Galperin MY, et al: Comparative genomics of the Archaea (Euryarchaeota): evolution of conserved protein families, the stable core, and the variable shell. Genome Res. 9:608–628. 1999.PubMed/NCBI

8 

Arcus VL, Backbro K, Roos A, Daniel EL and Baker EN: Distant structural homology leads to the functional characterization of an archaeal PIN domain as an exonuclease. J Biol Chem. 279:16471–16478. 2004. View Article : Google Scholar : PubMed/NCBI

9 

Lamanna AC and Karbstein K: Nob1 binds the single-stranded cleavage site D at the 3′-end of 18S rRNA with its PIN domain. Proc Natl Acad Sci USA. 106:14259–14264. 2009.PubMed/NCBI

10 

Fatica A, Tollervey D and Dlakic M: PIN domain of Nob1p is required for D-site cleavage in 20S pre-rRNA. RNA. 10:1698–1701. 2004. View Article : Google Scholar : PubMed/NCBI

11 

Fatica A, Oeffinger M, Dlakic M and Tollervey D: Nob1p is required for cleavage of the 3′ end of 18S rRNA. Mol Cell Biol. 23:1798–1807. 2003.

12 

Huang WY, Chen DH, Ning L and Wang LW: siRNA mediated silencing of NIN1/RPN12 binding protein 1 homolog inhibits proliferation and growth of breast cancer cells. Asian Pac J Cancer Prev. 13:1823–1827. 2012. View Article : Google Scholar : PubMed/NCBI

13 

Lu Z, Guo Q, Shi A, Xie F and Lu Q: Downregulation of NIN/RPN12 binding protein inhibits the growth of human hepatocellular carcinoma cells. Mol Biol Rep. 39:501–507. 2012. View Article : Google Scholar : PubMed/NCBI

14 

Lin Y, Peng S, Yu H, Teng H and Cui M: RNAi-mediated downregulation of NOB1 suppresses the growth and colony-formation ability of human ovarian cancer cells. Med Oncol. 29:311–317. 2012.

15 

Wu DP and He XW: Expression of NOB1 and its significance in colorectal cancer. Nan Fang Yi Ke Da Xue Xue Bao. 32:420–422. 2012.(in Chinese).

16 

Lin S, Meng W, Zhang W, et al: Expression of the NOB1 gene and its clinical significance in papillary thyroid carcinoma. J Int Med Res. 41:568–572. 2013.

17 

Oehler VG, Yeung KY, Choi YE, Bumgarner RE, Raftery AE and Radich JP: The derivation of diagnostic markers of chronic myeloid leukemia progression from microarray data. Blood. 114:3292–3298. 2009. View Article : Google Scholar : PubMed/NCBI

18 

Granneman S, Nandineni MR and Baserga SJ: The putative NTPase Fap7 mediates cytoplasmic 20S pre-rRNA processing through a direct interaction with Rps14. Mol Cell Biol. 25:10352–10364. 2005. View Article : Google Scholar : PubMed/NCBI

19 

Ramos PC, Hockendorff J, Johnson ES, Varshavsky A and Dohmen RJ: Ump1p is required for proper maturation of the 20S proteasome and becomes its substrate upon completion of the assembly. Cell. 92:489–499. 1998. View Article : Google Scholar : PubMed/NCBI

20 

Raychaudhuri S, Fontanes V, Barat B and Dasgupta A: Activation of ribosomal RNA transcription by hepatitis C virus involves upstream binding factor phosphorylation via induction of cyclin D1. Cancer Res. 69:2057–2064. 2009. View Article : Google Scholar : PubMed/NCBI

21 

Meraner J, Lechner M, Loidl A, et al: Acetylation of UBF changes during the cell cycle and regulates the interaction of UBF with RNA polymerase I. Nucleic Acids Res. 34:1798–1806. 2006. View Article : Google Scholar : PubMed/NCBI

22 

Shirane M, Harumiya Y, Ishida N, et al: Down-regulation of p27Kip1 by two mechanisms, ubiquitin-mediated degradation and proteolytic processing. J Biol Chem. 274:13886–13893. 1999.PubMed/NCBI

23 

Xu G, Bernaudo S, Fu G, Lee DY, Yang BB and Peng C: Cyclin G2 is degraded through the ubiquitin-proteasome pathway and mediates the antiproliferative effect of activin receptor-like kinase 7. Mol Biol Cell. 19:4968–4979. 2008. View Article : Google Scholar : PubMed/NCBI

24 

Fasanaro P, Capogrossi MC and Martelli F: Regulation of the endothelial cell cycle by the ubiquitin-proteasome system. Cardiovasc Res. 85:272–280. 2010. View Article : Google Scholar : PubMed/NCBI

25 

Niculescu AB III, Chen X, Smeets M, Hengst L, Prives C and Reed SI: Effects of p21Cip1/Waf1 at both the G1/S and the G2/M cell cycle transitions: pRb is a critical determinant in blocking DNA replication and in preventing endoreduplication. Mol Cell Biol. 18:629–643. 1998.

26 

Gu Y, Turck CW and Morgan DO: Inhibition of CDK2 activity in vivo by an associated 20K regulatory subunit. Nature. 366:707–710. 1993.PubMed/NCBI

27 

Harper JW, Adami GR, Wei N, Keyomarsi K and Elledge SJ: The p21 Cdk-interacting protein Cip1 is a potent inhibitor of G1 cyclin-dependent kinases. Cell. 75:805–816. 1993. View Article : Google Scholar : PubMed/NCBI

28 

Cai K and Dynlacht BD: Activity and nature of p21WAF1 complexes during the cell cycle. Proc Natl Acad Sci USA. 95:12254–12259. 1998. View Article : Google Scholar : PubMed/NCBI

29 

Ogryzko VV, Wong P and Howard BH: WAF1 retards S-phase progression primarily by inhibition of cyclin-dependent kinases. Mol Cell Biol. 17:4877–4882. 1997.PubMed/NCBI

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2014-March
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Li Y, Ma C, Qian M, Wen Z, Jing H and Qian D: Downregulation of NOB1 suppresses the proliferation and tumor growth of non-small cell lung cancer in vitro and in vivo Retraction in /10.3892/or.2020.7483. Oncol Rep 31: 1271-1276, 2014
APA
Li, Y., Ma, C., Qian, M., Wen, Z., Jing, H., & Qian, D. (2014). Downregulation of NOB1 suppresses the proliferation and tumor growth of non-small cell lung cancer in vitro and in vivo Retraction in /10.3892/or.2020.7483. Oncology Reports, 31, 1271-1276. https://doi.org/10.3892/or.2014.2991
MLA
Li, Y., Ma, C., Qian, M., Wen, Z., Jing, H., Qian, D."Downregulation of NOB1 suppresses the proliferation and tumor growth of non-small cell lung cancer in vitro and in vivo Retraction in /10.3892/or.2020.7483". Oncology Reports 31.3 (2014): 1271-1276.
Chicago
Li, Y., Ma, C., Qian, M., Wen, Z., Jing, H., Qian, D."Downregulation of NOB1 suppresses the proliferation and tumor growth of non-small cell lung cancer in vitro and in vivo Retraction in /10.3892/or.2020.7483". Oncology Reports 31, no. 3 (2014): 1271-1276. https://doi.org/10.3892/or.2014.2991