Elevated PABPC4 expression in human prostate cancer tissues predicts adverse clinical outcomes

Introduction

Prostate cancer (PCa), as one of the most common malignant tumors of the male urinary and reproductive system, has been on the rise globally, especially in China, where it has become the leading urological tumor affecting male health (1-3). This disease not only seriously threatens patients’ quality of life but also attracts much attention due to its high mortality rate. One of the important features of PCa in China is that the proportion of patients diagnosed at an advanced stage is significantly higher than in Western countries (4). Therefore, postoperative patients urgently need highly efficient biomarkers for recurrence monitoring and survival management. As medical research progresses, it becomes increasingly important to explore the molecular mechanisms of PCa development and identify biomarkers that can accurately predict tumor prognosis and guide individualized treatment.

Poly(A) binding protein cytoplasmic 4 (PABPC4), a member of the poly(A) binding protein (PABP) family, primarily functions by binding to the 3' poly(A) tails of most eukaryotic mRNAs, thereby playing a pivotal role in gene expression regulation (5,6). PABPC4 contains four ribonucleic acid (RNA) recognition motifs and a proline-rich C-terminus, enabling RNA binding (7,8). Notably, PABPC4 undergoes significant upregulation during T-cell activation, with its messenger RNA (mRNA) levels increasing approximately fivefold, suggesting a vital role in modulating the stability of labile mRNAs in activated T-cells. Furthermore, PABPC4 has been identified as activated platelet protein-1 (APP1), expressed on thrombin-activated platelets and megakaryocytes, hinting at its potential involvement in protein translation regulation or poly(A) binding and stabilization in these cells (9). In recent years, the functions of PABPC4 in various tumors have garnered increasing attention (10-14). In hepatocellular carcinoma (HCC), PABPC4, acting as a downstream gene of c-Myc, participates in gene expression regulation, fostering tumor cell proliferation and migration (15). These findings underscore the unique role of PABPC4 in tumorigenesis, offering novel molecular targets for early cancer diagnosis and targeted therapy. However, there is still a lack of studies that have elaborated on the expression of PABPC4 in PCa tissues and its impact on the prognosis of PCa.

In the present study, we aim to investigate the expression profile of PABPC4 through database retrieval, analysis of sequencing data from our group, and tissue immunohistochemistry (IHC). In addition, we investigated the prognostic value of PABPC4 in patients with PCa. We present this article in accordance with the REMARK reporting checklist (available at https://tau.amegroups.com/article/view/10.21037/tau-2025-19/rc).

Methods

Gene expression data collection

PCa gene expression data were sourced from The Cancer Genome Atlas (TCGA) via the TCGA Data Portal (https://tcga-data.nci.nih.gov/tcga/). We retrospectively analyzed 495 cases of PCa and 52 normal controls, systematically collecting and documenting their clinicopathological characteristics. In addition, sequencing data from PCa cases treated at our institution were incorporated into the study. This included sequencing data from 65 untreated PCa patients alongside their corresponding adjacent normal prostate tissues, acquired using previously established methodologies (16). Moreover, our analysis encompassed whole-genome, whole-transcriptome, and deoxyribonucleic acid (DNA) methylation data which called Chinese Prostate Cancer Genome and Epigenome Atlas (CPGEA) derived from 208 paired tumor tissue samples, which were matched with healthy control tissues from Chinese patients with primary PCa (17). To further substantiate our findings, three independent Gene Expression Omnibus (GEO) datasets (GSE6752, GSE21034, GSE32571) were retrieved and analyzed to evaluate the expression of PABPC4.

Construction of tissue microarrays (TMAs)

This study encompassed 210 patients who underwent prostatectomy at the Department of Urology, Changhai Hospital, between April 2011 and December 2015. Tissue specimens were procured from the Department of Pathology. Patients who had received preoperative treatments, such as endocrine therapy or radiotherapy, or who presented with secondary tumors were excluded from the analysis. Clinical and pathological data were meticulously extracted from the electronic medical records system. Cancer staging was conducted in accordance with the 8^th edition of the American Joint Committee on Cancer (AJCC) guidelines (18). Postoperatively, all patients were advised to undergo regular prostate-specific antigen (PSA) testing: every 3 months during the first year, and every 6 months from the second to the fifth year. Follow-up data were obtained from patient medical history records during the follow-up period, the institutional “PC-follow” database, and telephone interviews with patients or their relatives. Biochemical recurrence (BCR) was defined as a sustained serum PSA level exceeding 0.2 ng/mL, with the recurrence date established as the first instance of a PSA level of 0.2 ng/mL or higher. Formalin-fixed, paraffin-embedded tissue samples of PCa were retrieved from the pathology archives and independently assessed by two pathologists. A total of 210 tumors cores of 1-mm paraffin-embedded tissue cores were utilized to construct three TMAs. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by ethics committee of Shanghai Changhai Hospital (No. CHEC2019-012). The requirement for informed consent was waived because clinical data, including patient information and laboratory test results, were retrospectively obtained and analyzed.

IHC and expression level evaluation

IHC was conducted on 3 µm sections of TMAs using the PABPC4 antibody (14960-1-AP, 1:250, PROTEINTECH, Wuhan, China). Antigen retrieval, following deparaffinization and hydration, was performed using an automated Leica AutoStainer XL instrument (Leica, Wetzlar, Germany), in accordance with the manufacturer’s instructions. The sections were subsequently stained using the UltraSensitive™ SP IHC kit (Mouse/Rabbit, Maxim, Fuzhou, China) per the provided protocol. Prior to TMA staining, the antibody was validated against positive controls, as recommended by the PROTEIN ATLAS (https://www.proteinatlas.org/). Stained TMA sections were digitized using the NanoZoomer S60 scanner (HAMAMATSU, Japan) and analyzed with NDP viewer (HAMAMATSU, Japan). Regions of interest within each core were meticulously outlined and evaluated by two independent uro-pathologists. If the two were inconsistent, the judgment was entrusted to a third experienced doctor, and the expression degree of PABPC4 in each IHC stain was ultimately obtained.

Statistical analysis

Statistical analyses were conducted using SPSS software, version 25.0 (IBM, Armonk, NY, USA). The Wilcoxon signed-rank test was applied to compare the expression level of PABPC4 between tumor tissues and normal tissues, including adjacent normal and benign prostatic hyperplasia (BPH) tissues. RNA was extracted from both tumor and matched normal tissues, followed by high-throughput sequencing on the Illumina platform. RNA data analysis was conducted using tools such as TopHat and DESeq2, to identify differentially expressed genes and associated mutations (16,17). The Kruskal-Wallis test was utilized to evaluate the correlation between the expression level of PABPC4 and pathological tumor stage, postoperative Gleason score, and preoperative PSA levels. The Wilcoxon rank-sum test was used to assess associations between the expression level of PABPC4 and pathological lymph node status, prostate capsule invasion, surgical margin status, and seminal vesicle invasion. BCR-free survival was calculated from the date of surgery to the last follow-up or the date of observed recurrence. The association between the expression level of PABPC4 and BCR was analyzed using the log-rank test and Cox proportional hazards regression. Multivariate analysis incorporated factors such as pathological tumor stage (pT), metastasis stage (M stage), pathological lymph node stage (pN), Gleason score, and PSA levels. Recurrence and survival analyses were also performed using data from TCGA database, following identical methodologies. Additionally, the GEO database was queried to validate PABPC4 expression levels in PCa. A P value of ≤0.05 was considered statistically significant (two-tailed).

Results

PABPC4 RNA expression

In the 65 tumor-normal paired sequencing data, PABPC4 mRNA expression was significantly elevated in tumor tissues compared to adjacent normal tissues (Figure 1A; P<0.001). Additionally, PABPC4 expression levels correlated with Gleason scores (Figure 1B; P=0.041). Similarly, in the CPGEA dataset, higher PABPC4 mRNA expression was observed in tumor tissues relative to adjacent normal tissues (Figure 1C; P<0.001), with a similar trend was observed in the comparison across M stages (Figure 1D; P=0.051). Consistent findings were noted in the TCGA database, where PABPC4 mRNA expression was higher in tumor tissues compared to benign tissues (Figure 1E; P<0.001) and showed a correlation with tumor staging (Figure 1F; P=0.02). In both the GSE32571 (Figure 1G; P<0.001) and GSE21034 (Figure 1H; P<0.001) datasets, PABPC4 expression was also elevated in tumor tissues. However, in the GSE6752 dataset (Figure 1I; P<0.001), PABPC4 expression was significantly reduced in metastatic tumors.

Figure 1 Expression profile of PABPC4 across various datasets. (A) Comparison of relative PABPC4 mRNA expression between tumor and benign tissues in our 65 tumor-normal paired sequencing data (P<0.001). (B) PABPC4 mRNA expression patterns across different Gleason scores within the same dataset (P=0.041). (C) Relative PABPC4 mRNA expression in tumor versus benign tissues in the CPGEA dataset (P<0.001). (D) Expression patterns of PABPC4 mRNA across pathological M stages in the CPGEA data (P=0.051). (E) Comparison of PABPC4 mRNA levels between tumor and benign tissues in the TCGA dataset (P<0.001). (F) PABPC4 mRNA expression across tumor stages in the TCGA data (P=0.02). (G) Elevated PABPC4 mRNA expression in tumor tissues compared to normal tissues in the GSE32571 dataset (P<0.001). (H) Similar elevation in the GSE21034 dataset (P<0.001). (I) Higher PABPC4 protein expression in primary tumors versus metastatic tumors in the GSE6752 dataset (P<0.001). CPGEA, Chinese Prostate Cancer Genome and Epigenome Atlas; M, metastasis; PABPC4, poly(A) binding protein cytoplasmic 4; TCGA, The Cancer Genome Atlas.

PAPBC4 expression in TMA

Representative PABPC4 expression levels are shown in Figure 2. Table 1 summarizes the clinicopathological characteristics of all patients included in the study. A total of 210 patients were enrolled, with a mean age of 66.6 years [standard deviation (SD): 7.13 years]. Due to missing pathological information in the medical records system, some patients’ data were excluded from the analysis. All pathological results were visually confirmed by a senior pathologist. The relationship between clinicopathological parameters and PABPC4 expression is summarized in Table 2. There were no significant differences between low and high PABPC4 expression groups in terms of age, body mass index (BMI), preoperative PSA levels, pathological lymph node stage, International Society of Urological Pathology (ISUP) grade, prostate capsule invasion, seminal vesicle invasion, surgical margin status, or nerve invasion. However, there is a notable trend indicating that higher PABPC4 expression may be associated with more advanced pathological tumor stages, although this did not reach statistical significance (P=0.07). Overall, most clinicopathological features did not exhibit a significant correlation with PABPC4 expression levels.

Figure 2 PABPC4 expression pattern in prostate cancer tissues. (A) PABPC4 low expression. (B) PABPC4 high expression. Scale bars =500 µm in round slice; scale bars =100 µm in red square which is a magnified black box. IHC stain. IHC, immunohistochemistry; PABPC4, poly(A) binding protein cytoplasmic 4.

Association between PABPC4 expression and survival

The Kaplan-Meier survival curves (Figure 3) highlight the influence of PABPC4 expression on various survival metrics. In Figure 3A, BCR survival among 210 patients shows a significant disparity between those with high versus low PABPC4 expression (log-rank P=0.004), with higher expression correlating with poorer outcomes. For overall survival (OS) in the same cohort (Figure 3B), no significant difference is observed between the expression groups (log-rank P=0.96). Conversely, OS data from the TCGA cohort (Figure 3C) reveals that elevated PABPC4 expression is significantly associated with decreased survival (log-rank P=0.04). Similarly, disease-specific survival (DSS) in the TCGA cohort (Figure 3D) shows a significant link between higher PABPC4 expression and poorer DSS outcomes (log-rank P=0.02).

Figure 3 Relationship between PABPC4 expression and patient prognosis. (A) BCR time in the cohort of 210 patients (P=0.004). (B) OS in the cohort of 210 patients (P=0.96). (C) OS in patient data retrieved from the TCGA database (P=0.04). (D) DSS analysis from the TCGA database (P=0.02). BCR, biochemical recurrence; DSS, disease-specific survival; OS, overall survival; PABPC4, poly(A) binding protein cytoplasmic 4; TCGA, The Cancer Genome Atlas.

In both univariate and multivariate analyses, high PABPC4 expression was significantly associated with shorter BCR-free survival [hazard ratio (HR) =2.25, 95% confidence interval (CI): 1.45–3.49, P<0.001], indicating its potential as an independent prognostic marker. Additionally, elevated preoperative PSA levels (P=0.003) and lower postoperative ISUP grades (P=0.003) were independently associated with an increased risk of BCR. In contrast, other factors such as surgical margin status and pT category were not significant after adjustment (Table 3).

Discussion

PCa, a significant health issue affecting elderly males, despite the favorable outcomes attained through radical surgery in early-stage patients, remains a formidable challenge in terms of prognosis for those in advanced stages or with recurrent/metastatic disease (19,20). Hence, the pursuit of novel biomarkers for early detection, precise diagnosis, and treatment guidance is of paramount importance. The PABPC4 protein, a multifunctional entity, has recently drawn attention in colorectal cancer research due to its overexpression being associated with a poor prognosis (14). Nevertheless, the expression status and potential mechanisms of PABPC4 in PCa have remained largely unexplored, Offering a promising avenue for PCa biomarker development.

In this study, we explored the expression of PABPC4 in PCa and normal prostate tissues by employing sequencing data. This overexpression across datasets suggests PABPC4 drives PCa aggressiveness, beyond mere presence in tumors. At the mRNA level, the expression of PABPC4 was significantly elevated in PCa tissues compared with non-cancerous prostate tissues. In diverse subgroups of PCa tissues, the expression of PABPC4 decreased as the Gleason score increased. Nevertheless, the higher the tumor stage, the greater the expression of PABPC4. For further exploration, we utilized the GEO database (GSE6752) and demonstrated that the expression of PABPC4 declined with tumor progression. The opposing trends in PABPC4 expression in metastatic warranting further investigation. After analyzing the data in the TCGA database regarding OS and disease-free specific progression, we discovered that patients with low PABPC4 expression tended to have a longer disease-free survival. Subsequently, the analysis of follow-up data from TMA patients indicated that the expression of PABPC4 was significantly associated with the prognosis of PCa patients in both univariate and multivariate analyses, and a high expression of PABPC4 was regarded as an important factor for predicting poor BCR. Furthermore, a high expression of PABPC4 was associated with a shorter BCR-free time in survival analysis. Hence, we propose that PABPC4 can serve as a prognostic indicator for disease progression in PCa. To date, the precise role of PABPC4 in PCa differentiation remains unclear; however, our findings reflecting its link to aggressive disease and worse prognosis.

As a member of the PABP family, PABPC4 possesses distinctive structural characteristics that enable it to bind to the poly(A) tail of mRNA, thereby participating in the regulation of mRNA stability, translation efficiency, and intracellular localization (5,21). Studies in HCC have shown that PABPC4 promotes tumor cell proliferation, migration, and invasion by influencing the post-transcriptional regulation of specific genes, thereby contributing to tumorigenesis and progression (12). Although the specific mechanisms of PABPC4 in PCa are yet to be fully clarified, advancements in other tumor types offer enlightening cues (22). In the future, by exploring the upstream and downstream regulatory networks of PABPC4 in PCa, we aim to elucidate its crucial role in tumor initiation and progression, potentially leading to novel therapeutic targets for precision medicine in PCa.

Conclusions

We have discovered an association between PABPC4 expression and PCa, highlighting its potential as a prognostic biomarker, though its contribution to PCa pathogenesis awaits mechanistic proof. Additionally, we have demonstrated that PABPC4 expression in PCa lesions may be correlated with patient prognosis. Further research is necessary to unravel the mechanisms underlying PABPC4’s potential role in facilitating PCa progression.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the REMARK reporting checklist. Available at https://tau.amegroups.com/article/view/10.21037/tau-2025-19/rc

Data Sharing Statement: Available at https://tau.amegroups.com/article/view/10.21037/tau-2025-19/dss

Peer Review File: Available at https://tau.amegroups.com/article/view/10.21037/tau-2025-19/prf

Funding: This work was supported by Program of Shanghai Subject Chief Scientist (No. 22XD1405000).

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://tau.amegroups.com/article/view/10.21037/tau-2025-19/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by ethics committee of Shanghai Changhai Hospital (No. CHEC2019-012). The requirement for informed consent was waived because clinical data, including patient information and laboratory test results, were retrospectively obtained and analyzed.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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