The Gene Expression Profiling Interactive Analysis (GEPIA; http://gepia.cancer-pku.cn/) and Gene Expression Omnibus (GEO; http://www.ncbi.nlm.nih.gov/geo/) databases were utilized to assess the mRNA expression levels of KLC3 in OC. The Cancer Genome Atlas (TCGA) TCGA-OV data (https://www.cancer.gov/ccg/research/genome-sequencing/tcga) and the Genotype-Tissue Expression normal ovarian tissue data (https://commonfund.nih.gov/genotype-tissue-expression-gtex) were obtained from the GEPIA, and the GSE12470 (17) and GSE18520 (18) datasets were obtained from the GEO. Tumor samples in all databases were not matched to normal samples, the normal samples were from healthy individuals. Additionally, the Kaplan-Meier plotter (http://kmplot.com/analysis/) was employed to investigate the association between KLC3 expression and the prognosis of patients with OC.

Five patients with OC who underwent surgery at The First Hospital of Lanzhou University (Lanzhou, China) between June 2022 and November 2022, along with five normal ovarian samples (healthy controls), were collected for western blot analysis. The average age of the healthy control group for western blotting and IHC was 60 years old, including women aged between 55 and 62 years old. Ovarian samples were obtained following hysterectomy for benign gynecological diseases, such as abnormal uterine bleeding, adenomyosis, uterine fibroids and uterine abscess. Furthermore, 48 OC tissues and 10 normal tissues collected from healthy controls were obtained between January 2020 and January 2023 were used for immunohistochemistry (IHC). Table I provides the basic features of the patients, and International Federation of Gynecology and Obstetrics staging was used in all patients (19). All patients were diagnosed with OC through pathological examination and their clinical data were recorded. None of the patients had received targeted therapy, chemotherapy or radiotherapy prior to surgery. The present study was approved by the Ethics Committee of The First Hospital of Lanzhou University (approval no. LDYYLL-2019-279), and all tissues involved in the present study were stored in the Biobank of The First Hospital of Lanzhou University, where all samples were stored with the consent of patients. The medical records were available for the participants, and all participants provided written informed consent and their samples were anonymized. The current study was conducted in compliance with the International Conference on Harmonization guidelines for Good Clinical Practice (20) and the 2013 Declaration of Helsinki. The SKOV3 and A2780 human OC cell lines used in the present study were sourced from the Cell Resource Center, Institute of Basic Medicine, Chinese Academy of Medical Sciences. All cells were cultured in DMEM (Gibco; Thermo Fisher Scientific, Inc.) supplemented with 10% FBS, 10 mg/ml streptomycin, 10,000 U/ml penicillin and 25 µg/ml amphotericin B (all from Gibco; Thermo Fisher Scientific, Inc.) at 37°C and 5% CO₂.

The lentivirus design and packaging were provided by Shanghai GeneChem Co., Ltd. The experimental group was divided into two groups: The knockdown group and the overexpression group. The knockdown groups included the short hairpin (sh)RNA negative control (NC), shKLC3-64#, shKLC3-65# and shKLC3-66# groups, and the overexpression groups included the Vector (empty vector) and KLC3 groups. All SKOV3 and A2780 cells were cultured in a constant temperature incubator at 37°C and 5% CO₂. According to the transduction instructions, KLC3 knockdown plasmids with a pPLK GFP+Puro plasmid backbone were provided by Shanghai GeneChem Co., Ltd. The 2nd generation system was used for plasmid packaging. A total of 1.5 µg knockdown plasmids, 1 µg pCMV–VSV-G and 0.5 µg pCAG-dR8.9 (both from Beyotime Institute of Biotechnology) were transfected into 293T cells (The Cell Bank of Type Culture Collection of The Chinese Academy of Sciences) in 6-well plates using Lipofectamine^® 3000 transfection reagent (Invitrogen; Thermo Fisher Scientific, Inc.) according to the manufacturer's instructions at 37°C. Lentiviral particles were harvested 48 h post-transfection, followed by infection of SKOV3 OC cells for 24 h. Cells (30% confluence) were seeded in cell culture dishes and were infected with lentiviral plasmids at multiplicity of infection (MOI) of 10. At 37°C and screening of the cells for 7 days with medium containing 2 µg/ml puromycin (Beyotime Institute of Biotechnology). The target sequences of the knockdown lentiviral plasmids were as follows: shNC, 5′-TGTCGCGGTAAGTGCCTCATA-3′; shKLC3-64#, 5′-CAACAACTTGGCTGTCCTCTA-3′, shKLC3-65#, 5′-GACCCTGCATAACCTCGTGAT-3′ and shKLC3-66#, 5′-GCCACAGACCTTCTCCATGAT-3′.

In order to construct a plasmid for overexpressing KLC3, full-length human KLC3 cDNA was first cloned into a p-Enter plasmid (Shanghai GeneChem Co., Ltd.). The p-Enter-KLC3 construct was then recombined into a Lenti-CMV expression vector to generate the final Lenti-CMV-KLC3 plasmid for lentiviral packaging. Lentiviral particles were produced by co-transfecting the Lenti-CMV-KLC3 or Lenti-CMV-vector (negative control) plasmids with the packaging plasmid pSPAX2 and the envelope plasmid pMD2.G into 293T cells (~70% confluence in 6-well plates) using Lipofectamine 3000 at 37°C, according to the manufacturer's protocol. After 6 h of transfection, the medium was replaced with fresh complete medium. For lentiviral transfection, the ratio of lentiviral plasmid to packaging and envelope plasmids was Lenti-CMV-KLC3/Lenti-CMV-vector: pSPAX2 (packaging plasmid): pMD2G (envelope plasmid)=1:1:0.5 µg. After 36 h of culture, the virus was harvested from the supernatant and concentrated with lenti-X-concentrator (Shanghai GeneChem Co., Ltd.), and then added to A2780 cells along with 5 µg/ml polybrene (Beyotime Institute of Biotechnology). Cells (30% confluence) were seeded in cell culture dishes and were infected with lentiviral plasmids at a MOI of 15 at 37°C. The cells were initially selected with medium containing 2.0 µg/ml puromycin (Beyotime Institute of Biotechnology) for 48 h. The medium was then replaced with medium containing 5.0 µg/ml puromycin, which was used for maintenance over a 7-day period to establish stable cell lines. Western blotting was employed to verify the infection efficiency, with the Lenti-CMV-vector serving as the control.

For COL3A1 overexpression, SKOV3 cells were transfected with a pcDNA3.1 plasmid (2 µg) encoding COL3A1 cDNA, whereas empty vectors served as the NC group. All plasmids were synthesized by Beijing Sino Technology Co. Ltd. The SKOV3 cells were seeded in 6-well plates at a density of 1×10⁶/well were transfected with the aforementioned plasmids (10 µg) using Lipofectamine 2000 for 48 h at 37°C according to the manufacturer's instructions. The cells were collected for subsequent experiments 48 h post-transfection. In addition, in the cells with both KLC3 knockdown and COL3A1 overexpression, SKOV3 cells were transfected for 48 h with the COL3A1 plasmid after infection with shKLC3. In addition, western blotting was used to verify the transfection efficiency.

TRIzol^® reagent (Invitrogen; Thermo Fisher Scientific, Inc.) was used to extract total RNA from SKOV3 and A2780 cells, A NanoDrop 2000 spectrophotometer was used to measure the RNA concentration, and cDNA was synthesized by RT of 1 µg total RNA according to the manufacturer's protocol of the RT kit (cat. no. R233-01; Vazyme Biotech Co., Ltd.). A qPCR machine was used to amplify cDNA using the SYBR Green qPCR Mix (cat. no. Q711-02; Vazyme Biotech Co., Ltd.). The thermocycling conditions for amplification were as follows: 95°C for 5 min, followed by 40 cycles at 95°C for 10 sec, 60°C for 30 sec and a final step at 95°C for 15 sec, 60°C for 60 sec and 95°C for 15 sec. GAPDH was used as an internal control. Subsequently, the 2^−ΔΔCq method was used to analyze the gene expression data (21). β-actin was used as an internal control. The primer sequences were as follows: β-actin, forward 5′-GCGTGACATTAAGGAGAAGC-3′, reverse 5′-CCACGTCACACTTCATGATGG-3′; KLC3, forward 5′-CTCAACATCCTGGCGCTGGT-3′, reverse 5′-TCCCGGTAACGCCCACGCTTC-3; CXCL12, forward 5′-TGCCCTTCAGATTGTAGCCC-3′, reverse 5′-CTGTAAGGGTTCCTCAGGCG-3′; IGFL3, forward 5′-TGCTGTCCCGAGTCTTTTGG-3′, reverse 5′-GTGCCTCCTGTTCCTGGTA-3′; COL3A1, forward 5′-TAAAGGCGAAATGGGTCCCG-3′, reverse 5′-GGCACCATTCTTACCAGGCT-3′; COL1A2, forward 5′-GAGGAGAGCCTGGCAACATT-3′, reverse 5′TCCACCTTGAACACCCTGTG-3′; TENM2, forward 5′-CAAAGAGTGTCGCTACACAAGC-3′, reverse 5′-TCCTGCTGTCATGGTCATAGG-3′; CREB3L1, forward 5′-TGGAGAATGCCAACAGGACC-3′, reverse 5′-CCAGCACCAGAACAAAGCAC-3′; MMP13, forward 5′-CAGTTTGCAGAGCGCTACCT-3′, reverse 5′-TTCTCGGAGCCTCTCAGTCA-3′; IGFBP5, forward 5′-ACAAGAGAAAGCAGTGCAAACC-3′, reverse 5′-CGTCAACGTACTCCATGCCT-3′; SLC14A1, forward 5′-AGCCAGCTAGAGTGGTCTTT-3′, reverse 5′-TCCAAACAGGACCATGACGG-3′; SPARC, forward 5′-TTCGGCATCAAGCAGAAGGAT-3′, reverse 5′-TTAGCACCTTGTCTCCAGGC-3′.

A total of 12 4-week-old female BALB/c nude mice (weight, 15–16 g) were purchased from Beijing Vital River Laboratory Animal Technology Co., Ltd. The mice were housed in the animal facility under standard conditions, with a controlled temperature of 25±2°C and humidity of 55±5%, under a 12-h light/dark cycle, with free access to water and food. Each mouse received a subcutaneous injection of 100 µl (5×10⁶) cell suspension into the right flank with shNC-infected SKOV3 cells, shKLC3-infected SKOV3 cells, Vector-infected A2780 cells or KLC3-overexpressing A2780 cells. The study was terminated based on tumor volume (~1,500 mm³) as the humane endpoint. Mice injected with shNC-infected SKOV3 cells and shKLC3-infected SKOV3 cells were sacrificed on day 24, whereas mice injected with Vector-infected A2780 cells and KLC3-overexpressing A2780 cells were sacrificed on day 21. Notably, no mice succumbed before reaching the humane endpoint criteria. Tumor volume was measured twice per week using electronic calipers and the animals were weighed five times per week. At the end of the study, mice were euthanized by CO₂ asphyxiation (30% vol/min) followed by cervical dislocation as noted in the IACUC-approved protocol, and the tumors were excised, weighed and cut in half. No analgesics were administered during the study since flank tumor studies are considered painless. Animal experiments were approved by the Animal Experimental Ethics Committee of The First Hospital of Lanzhou University (approval no. LDYYLL-2023-495).

Samples were fixed in 10% neutral formalin fixative solution (BBI Solutions) embedded in paraffin at room temperature overnight, and divided into 3-µm sections, which were deparaffinized with xylene and then rehydrated with a succession of decreasing alcohol concentrations (100, 95, 85, 70 and 50% ethanol). Tissue sections were then placed in antigen retrieval buffer (pH 9.0; Wuhan Servicebio Technology Co., Ltd.) in a microwave oven on medium power for 8 min until boiling, then cooled for 8 min and switched to medium-low power for 7 min. After natural cooling, the slides were placed in PBS (pH 7.4; Wuhan Servicebio Technology Co., Ltd.) and washed three times on a destaining shaker. Subsequently, 3% hydrogen peroxide solution was added to the sample at room temperature for 25 min to block endogenous peroxidase, followed by blocking with 3% BSA (Sangon Biotech Co., Ltd.) at room temperature for 30 min. The histological sections were then incubated at 4°C overnight with rabbit anti-KLC3 antibody (1:200; cat. no. ab180523; Abcam) and anti-PCNA antibody (1:200; cat. no. 10205-2-AP; Proteintech Group, Inc.), and with a horseradish peroxidase-conjugated goat anti-rabbit IgG secondary antibody (1:200; cat. no. SA00001-2; Proteintech Group, Inc.) at 37°C for 30 min. Sections were then counterstained with 0.1% hematoxylin (Boster Biological Technology) at room temperature for 2 min and were stained with the chromogen DAB (Boster Biological Technology). With an objective magnification of ×200 or ×400, histological images were captured using a light microscope (cat. no. AE2000; Motic Incorporation, Ltd.). A total of 10 normal ovarian tissue samples and 48 OC tissue samples, as well as mouse tumor tissues were selected for assessing expression levels. The IHC scores were independently evaluated by two pathologists. Staining intensity was categorized as 0, no staining; 1, weak staining; 2, moderate staining; and 3, strong staining. Based on the extent of brown staining, the stained area was divided into percentages ranging from 1 to 99%. Finally, the staining intensity and stained area were each multiplied by 100. The patients were divided into two groups, high and low expression, according to the median value.

For the CCK-8 assay, wild-type and infected cells were seeded in 96-well plates and incubated with CCK-8 Reagent (Shanghai Yeasen Biotechnology Co., Ltd.) for 2 h over 5 consecutive days. The CCK-8 reagent was added for a 2-h incubation period. Absorbance at 450 nm was subsequently measured using a microplate reader.

Wild-type and infected/transfected cells were seeded at a density of 500 cells/well in 6-well plates. After 14 days, the cells were stained with 10% Giemsa (Beijing Biotopped Technology Co., Ltd.) at room temperature for 10 min after being fixed with methanol at room temperature for 30 min. To assess the colony formation capacity of the cells, visible colonies were counted. A dense conglomerate of cells was regarded as a colony when the number of cells exceeded 50. ImageJ software [Fiji (https://imagej.net/software/fiji/downloads) (National Institutes of Health)] was used to count the number of colonies. This experiment was repeated three times.

Cells were cultured in 6-well plates until they reached ~30% confluence. The transduced cells were subsequently trypsinized and collected by centrifugation at 1,200 × g for 5 min at 4°C, forming a compact pellet. After washing, the cells were resuspended in 200 µl ice-cold 1X PBS. Subsequently, the cell suspension was carefully mixed at a ratio of 1:10 with low melting point agarose maintained at 42°C and was promptly pipetted onto the designated CometSlide™ area (Shanghai Yeasen Biotechnology Co., Ltd.). Slides were incubated in the dark at 4°C for 30 min, followed by immersion in chilled lysis solution (Trevigen, Inc.; Bio-Techne) at 4°C for 30 min. The slides were then incubated in alkaline unwinding buffer (0.3 N NaOH, 1 mM EDTA) at room temperature for 30 min. The slides were then transferred to a horizontal electrophoresis chamber and subjected to electrophoresis using buffer (0.3 N NaOH, 1 mM EDTA) at an electric field strength of 1 V·cm⁻¹ for 20 min. Following electrophoresis, the samples were dried and stained with ethidium bromide. The comet tails were visualized under a DM 2500 fluorescence microscope (Leica Microsystems GmbH) and were quantified using Komet 5.5 software (Andor Technology Ltd.). A minimum of 50 cells were analyzed per treatment condition. All experiments were conducted independently at least three times.

Infected/transfected cells were cultured to ~90% confluence in 12-well plates and a wound was introduced using a sterile 200-µl pipette tip. After washing twice with PBS, cells were cultured in DMEM/F12 without FBS for 48 h. Cell images were obtained using fluorescence microscopy (IX73; Olympus Corporation). Wound sizes were measured with ImageJ 1.5.2a software and were calculated as a percentage (from 0 to 24 h).

Transwell migration assays were conducted using 24-well plates fitted with membranes containing 8-µm pores (Corning, Inc.). Cells were seeded on the upper chamber without serum at a density of 2×10⁴ cells/well, whereas complete medium supplemented with 10% FBS, 10 mg/ml streptomycin, 10,000 U/ml penicillin and 25 µg/ml amphotericin B was added to the lower chamber. After a 24-h incubation period at 37°C, the cells were removed from the upper chamber using a cotton swab followed by fixation with 4% formaldehyde at room temperature for 30 min and staining with Giemsa solution at room temperature for 15 min. The assessment of migration involved counting cell numbers in 10 random fields under a light microscope (Leica Microsystems, Inc.); this process was repeated three times for accuracy and consistency.

For the apoptosis assay, the cells were harvested, washed with PBS, suspended in binding buffer and sequentially stained with the Annexin V-FITC Detection Kit (Roche Applied Science) according to the manufacturer's protocol. Subsequently, apoptotic cells were detected using a FacsCalibur flow cytometer (BD Biosciences), and the results were analyzed using CellQuest version 3.3 software (BD Biosciences). Each experiment was performed in triplicate.

Total proteins were extracted from cells and tissues using RIPA lysis buffer and PMSF at a ratio of 1:100 (Beyotime Institute of Biotechnology). Phosphorylated proteins were extracted separately with the addition of phosphatase inhibitors (Biosharp Life Sciences). The protein levels were quantified using a BCA assay kit. Subsequently, an equal volume of protein mixture (30 µg) was pipetted into the wells of the gel matrix (containing 30% acrylamide), and the electrical potential was fixed at 120 volts for the purpose of conducting gel electrophoresis. After a 30-min transfer, the PVDF membrane was immersed in a solution of 5% non-fat milk powder and blocked for 2 h at 25°C. Subsequently, membranes were washed three times with TBS-0.1% Tween 20 (TBST), followed by incubation with the primary antibodies overnight at 4°C, three further washes with TBST and incubation with a HRP-conjugated secondary antibody (anti-rabbit IgG; 1:5,000; cat. no. GTX213110; GeneTex, Inc.) for 2 h at 25°C. Chemiluminescent solution was then added for 10 sec for visualization. The following primary antibodies were used: KLC3 (1:1,000; cat. no. ab180523), E-cadherin (1:10,000; cat. no. ab40772), N-cadherin (1:10,000; cat. no. ab76011), Vimentin (1:5,000; cat. no. ab92547), Snail (1:1,000; cat. no. ab216347), GAPDH (1:5,000; cat. no. ab8245) and α-tubulin (1:10,000; cat. no. ab7291) (all from Abcam); PALB2 (1:2,000; cat. no. 14340-1-AP), XRCC1 (1:1,000; cat. no. 21468-1-AP), XRCC2 (1:20,000; cat. no. 20285-1-AP) and COL3A1 (1:1,000; cat. no. 22734-1-AP) (all from Proteintech Group, Inc.); AKT (1:1,000; cat. no. 9272), PI3K (1:1,000; cat. no. 4292), phosphorylated (p-)AKT (1:1,000; cat. no. 4060) and p85α (also known as p-PI3K; 1:1,000; cat. no. 4228) (all from Cell Signaling Technology, Inc.). Protein visualization was achieved using a highly sensitive ECL substrate kit (Beyotime Institute of Biotechnology). All results were normalized to the internal reference proteins GAPDH and tubulin. Densitometric analysis was carried out using ImageJ 1.5.2a software.

Total RNA was extracted from SKOV3 cells infected with shKLC3 and shNC using a RNeasy Mini Kit (Qiagen, Inc.), and RNA quality was assessed using an Agilent Bioanalyzer (Agilent Technologies, Inc.). Samples with RNA integrity number >7.0 were used for library preparation. A total of 4 µg DNase-treated RNA from each sample was used to construct cDNA libraries using the TruSeq Stranded Total RNA Library Prep Kit (cat. no. 20020597; Illumina, Inc.), according to the manufacturer's protocol. RNA was fragmented and subjected to two rounds of cDNA synthesis and adapter ligation. Libraries were quantified using qPCR (concentration >2 nM) and qualified using an Agilent 2100 Bioanalyzer. Paired-end 100 bp reads were generated on the Illumina NovaSeq 6000 and HiSeq X Ten platforms (NovaSeq 6000 S1 Reagent Kit, 300 cycles; cat. no. 20012863-1; Illumina, Inc.). High-quality reads were obtained by trimming adapters and filtering low-quality reads. Read alignment and differential gene expression analysis were performed using the DESeq2 package (v1.26.0; http://github.com/thelovelab/DESeq2), and genes with a false discovery rate-adjusted P-value (q-value) <0.05 were considered significantly differentially expressed.

Multivariate and principal component analyses were performed using the ClustVis online tool (https://github.com/fw1121/ClustVis). Functional enrichment analysis was performed using Metascape (https://metascape.org/gp/index.html#/main/step1) (22). Metascape pathway enrichment analysis uses Kyoto Encyclopedia of Genes and Genomes (https://www.genome.jp/kegg/kegg_ja.html), Reactome (https://reactome.org/) and MSigDB (https://www.gsea-msigdb.org/gsea/msigdb). Statistical significance of gene overrepresentation was assessed using a hypergeometric test (Fisher's exact test), followed by Bonferroni correction for multiple comparisons. Heatmaps and volcano plots were generated using TBtools (v 1.055; http://github.com/CJ-Chen/TBtools/releases).

Cells were lysed with 250 µl NP-40 lysis buffer (cat. no. P0013F; Beyotime Institute of Biotechnology) for 30 min on ice and then centrifuged at 16.2 × g and 4°C for 10 min to remove cell fragments. The protein lysate (200 µl), bound to 25 µl magnetic beads (cat. no. 88802; Thermo Fisher Scientific, Inc.) with anti-KLC3 (1:50; cat. no. ab180523; Abcam), anti- COL3A1 (1:50; cat. no. 22734-1-AP; Proteintech Group, Inc.) or IgG (1:200; cat. no. 10284-1-AP; Proteintech Group, Inc.) antibodies, was incubated overnight at 4°C. The next day, the magnetic beads were adsorbed using a magnetic grate and washed with lysis buffer (Thermo Fisher Scientific, Inc.). The lysis buffer was transferred to the newly washed column and incubated at 4°C for 2 h. After incubation, the supernatant was discarded and washed five times with 500 µl IP-specific lysis buffer (cat. no. 26149; Thermo Fisher Scientific, Inc.). Finally, KLC3 and COL3A1 levels were analyzed by western blotting using anti-KLC3 (1:200; cat. no. ab180523; Abcam) and anti-COL3A1 (1:200; cat. no. 22734-1-AP; Proteintech Group, Inc.) antibodies.

Statistical analysis was conducted using SPSS 20.0 software (IBM Corp.) and GraphPad Prism version 8.0.2 (Dotmatics). Each experiment was performed in triplicate and continuous data are presented as the mean ± standard deviation. The differences between experimental groups were analyzed using one-way ANOVA followed by Bonferroni's post hoc test or unpaired two-tailed Student's t-test. Survival analysis was performed using the Kaplan-Meier method and log-rank test. P<0.05 was considered to indicate a statistically significant difference.

To assess the relationship between KLC3 and OC, the present study initially examined the expression of KLC3 in the GEPIA database, which revealed high mRNA levels of KLC3 in OC compared with normal tissue (Fig. 1A). Subsequently, the present study investigated the expression of KLC3 in the GSE12470 and GSE18520 datasets, and its expression was also significantly elevated in OC tissues compared with in tissues from healthy controls in these datasets (Fig. 1B and C). The Kaplan-Meier curve analysis demonstrated that patients with OC and low KLC3 expression had a better prognosis in different probesets: 1570402_at (HR=1.39, 95% CI 1.13–1.7) and 239853_at (HR=1.52, 95% CI 1.24–1.87) (Fig. 1D and E). Additionally, the results of IHC indicated that the expression of KLC3 was higher in OC tissues than that in normal tissues (Fig. 1F). Western blot analysis of five OC samples and five normal samples also revealed an elevated expression of KLC3 in OC (Fig. 1G). Finally, based on the expression levels of KLC3 in OC, 48 patients were categorized into high and low expression groups. The results revealed that patients with OC and high KLC3 expression had a poorer overall survival rate (Fig. 1H). Based on these findings, it could be hypothesized that KLC3 serves a notable role in the development and progression of OC, warranting further investigation into its function.

The present study examined the mRNA and protein expression levels of KLC3 in two OC cell lines, SKOV3 and A2780. As shown in Fig. 2A, the expression of KLC3 was significantly higher in SKOV3 cells compared with that in A2780 cells. To investigate the functional role of KLC3 in OC, lentiviral knockdown of KLC3 was performed in the SKOV3 cell line and overexpression of KLC3 was induced in the A2780 cell line. Notably, shKLC3#66 exhibited optimal knockdown efficiency (subsequently denoted as shKLC3), achieving a knockdown rate of 80%, and the overexpression vector met the experimental standards for subsequent analyses (Fig. 2B).

To assess proliferation, the CCK-8 assay was performed over 5 consecutive days. The results revealed a significant reduction in proliferation following KLC3 knockdown, whereas proliferation was enhanced in response to KCL3 overexpression (Fig. 2C). The colony formation assay demonstrated diminished colony-forming ability following KCL3 knockdown relative to the control group, whereas this ability was enhanced post-KCL3 overexpression (Fig. 2D).

When investigating the relationship between KLC3 and apoptosis, it was revealed that knocking down KLC3 significantly increased the apoptosis of OC cells, whereas overexpression of KLC3 did not result in a noticeable change in apoptosis levels (Fig. 2E). Similarly, compared with in the control group, knockdown of KLC3 weakened the migratory ability of OC cells in the Transwell assay; however, overexpression of KLC3 did not lead to a significant change in the migratory ability of A2780 cells (Fig. 3A). In order to further investigate the underlying mechanisms, changes in EMT-related proteins, such as E-cadherin, N-cadherin, Snail and Vimentin, were examined through western blotting. It was observed that when the expression of KLC3 was knocked down, there was a corresponding decrease in the expression levels of N-cadherin, Snail and Vimentin, whereas an increase in E-cadherin expression was noted. Conversely, when KLC3 expression was increased, there was a concomitant increase in the expression levels of N-cadherin, Snail and Vimentin, with a decrease in E-cadherin expression (Fig. 3B).

DNA damage is a known instigator in the transformation of normal cells into tumor cells. In the context of cancer treatment, augmenting the efficacy of radiotherapy and chemotherapy involves impeding DNA damage repair in tumor cells through diverse modalities. The association between KLC3 expression and resistance to DNA damage in OC was substantiated through the comet assay. The reduced expression of KLC3 resulted in a marked increase in uncoiled and damaged DNA strands and fragments, whereas overexpression of KLC3 exhibited minimal impact on DNA damage (Fig. 3C). Examination of the DNA damage-associated proteins XRCC1, XRCC2 and PALB2 revealed that diminished expression of KLC3 corresponded to reduced expression levels of XRCC1, XRCC2 and PALB2; conversely, overexpression of KLC3 was associated with elevated levels of these proteins (Fig. 3D). These collective findings indicated that KLC3 may have a pivotal role in various malignant phenotypes, as well as anti-DNA damage repair mechanisms, within human OC cell lines.

The impact of KLC3 knockdown on tumor growth was assessed using a nude mouse xenograft model. Compared with in the control group, KLC3 knockdown impeded tumor growth (Fig. 4A), with a notably reduced growth rate compared with that in the control group (Fig. 4C). In addition, IHC analysis revealed decreased expression of KLC3 and its associated proliferation marker PCNA in the knockdown group (Fig. 4E). By contrast, overexpression of KLC3 stimulated in vivo tumor cell proliferation (Fig. 4B) and markedly increased tumor growth rate (Fig. 4D). The results of IHC indicated no significant difference in the expression levels of KLC3 and PCNA between the overexpression group and the control group (Fig. 4F). No difference in KLC3 expression was found after tumor formation; however, the overexpression efficiency of all cells was verified by western blotting before injection. These findings underscore the pivotal role of KLC3 in OC cell proliferation.

According to the high-throughput sequencing analysis, a total of 13,516 differentially expressed genes were identified between the SKOV3-NC and SKOV3-shKLC3 groups. The screening criteria were set at fold change ≥2 and P<0.05, resulting in 376 differentially expressed genes, with 261 upregulated and 115 downregulated (Fig. 5A and C). The top 10 downregulated genes were validated by PCR, and it was revealed that seven were significantly decreased and three showed no change between the shKLC3 and NC groups; COL3A1 exhibited the most significant difference (Fig. 5D). Western blotting results demonstrated that KLC3 knockdown led to decreased COL3A1 levels (Fig. 5E). Pathway enrichment analysis revealed that the ‘PI3K-Akt signaling pathway’ was the most enriched (8.57%), followed by the ‘TNF signaling pathway’ (7.43%) among others (Fig. 5B). The western blot analysis results for AKT, PI3K, p-AKT and p85α confirmed that decreased KLC3 expression did not affect the levels of AKT and PI3K, whereas it did lead to a decrease in p-AKT and p38a levels. Conversely, increased KLC3 expression did not impact the levels of AKT and PI3K, but resulted in an increase in p-AKT and p38a expression (Fig. 5F). Therefore, these findings suggested that overexpression of KLC3 may promote COL3A1 expression and activate the PI3K/AKT signaling pathway in OC cells.

The aforementioned findings demonstrated that alterations in KLC3 can lead to changes in COL3A1 and activation of the PI3K/AKT pathway. To further investigate the mechanism by which KLC3 promotes the malignant progression of OC cells, the interaction between KLC3 and COL3A1 was examined using co-IP. The results revealed that there was an interaction between KLC3 and COL3A1 in SKOV3 cells (Fig. 6A). Furthermore, overexpression of COL3A1 in SKOV3 cells and in shKLC3-infected cells resulted in alterations in the expression of DNA damage-related genes and EMT-related genes; the expression levels of XRCC1, XRCC2, PALB2, N-cadherin, Snail and Vimentin were increased, whereas E-cadherin expression was decreased compared with in the shKLC3 group (Fig. 6B, C and E). Following overexpression of COL3A1, similar effects were observed when comparing it to knocking down KLC3 alone. Similarly, the overexpression of COL3A1 stimulated activation of the PI3K/AKT pathway, and overexpression of COL3A1 reversed the inhibitory effects of shKLC3 (Fig. 6D). The results of clonogenic (Fig. 6F), wound healing (Fig. 6G) and Transwell (Fig. 6H) assays revealed that the migratory and proliferative capabilities were increased in the shKLC3 + COL3A1 group compared with those in the shKLC3 group. These findings suggested that KLC3 may activate the PI3K/AKT pathway by interacting with COL3A1 and could contribute to the malignant functions of OC cells.