MEX3A promotes hepatocellular carcinoma cell proliferation and migration via the Wnt/β-catenin and EMT pathways

Abstract

In this paper, we focus on compelling evidence showing that MEX3A is significantly overexpressed in hepatocellular carcinoma (HCC) and correlates with poor prognosis. A recent study by Ji et al highlights MEX3A’s role in driving proliferation and migration via the RORA/β-catenin axis and epithelial-mesenchymal transition, positioning it as a potential biomarker and therapeutic target. This study addresses a critical gap in understanding HCC pathogenesis and offers valuable mechanistic insights.

Key Words: MEX3A; Hepatocellular carcinoma; Epithelial-mesenchymal transition; Biomarker; Proliferation; Migration

Core Tip: This analysis of The Cancer Genome Atlas data revealed that MEX3A mRNA expression is significantly higher in hepatocellular carcinoma (HCC) tissues compared to adjacent non-tumor tissues. High MEX3A expression was associated with worse overall survival in HCC patients. Knockdown of MEX3A in HCC cell lines (HepG2 and MHCC-97H) significantly inhibited cell proliferation and colony formation. MEX3A silencing induced cell cycle arrest at the G1 phase, accompanied by decreased expression of cyclin D1 and increased expression of the cell cycle inhibitor p21. MEX3A knockdown reduced the nuclear translocation of β-catenin (P < 0.05), a key component of the Wnt signaling pathway, and downregulated downstream targets such as c-Myc and cyclin D1. The development of treatments targeting genes with oncogenic alterations and related signaling pathways, based on advances in understanding of molecular cancer biology, is a major step in cancer treatment evolution.

TO THE EDITOR

Primary liver cancer ranks among the most prevalent and deadly malignancies, ranking sixth in incidence and third in mortality across all cancer types[1]. Hepatocellular carcinoma (HCC) constitutes a substantial portion, between 75% and 85%, of all liver cancer cases[2]. The treatment of HCC faces challenges due to its asymptomatic early stages, non-specific early symptoms, and propensity for metastasis and recurrence, resulting in less-than-optimal treatment outcomes. For liver cancer patients diagnosed during this specified period, the five-year survival rate stood at approximately 22%[3].

Advancements in cancer therapy, like chemotherapy, radiotherapy, and immunotherapy, have significantly enhanced survival rates of patients in recent years[4].

MEX3A belongs to the gene family MEX3 (comprising MEX3A, MEX3B, MEX3C, and MEX3D), situated on chromosome 1q22[5]. Initially identified in the nematode Caenorhabditis elegans (C. elegans), the MEX3A protein serves as a translational regulator, playing a role in suppressing the expression of plasminogen activator inhibitor-1 during early C. elegans embryonic development[6]. Further research into this gene has revealed its close association with the development of various diseases, including cancer. In bladder and ovarian cancers, MEX3A exhibits notably elevated expression levels in cancerous tissues compared to adjacent non-cancerous tissues[6,7]. Another study demonstrated that reducing MEX3A expression suppressed gastric cancer cell proliferation, migration, and cloning ability. The recent study by Ji et al[8] provides valuable insights into the role of MEX3A in promoting HCC cell proliferation via the RORA/β-catenin pathway.

Ji et al[8] used data from The Cancer Genome Atlas (TCGA) to examine MEX3A mRNA expression levels in HCC tissues and in adjacent non-cancerous tissues. They evaluated the correlation between MEX3A expression and overall survival (OS) among the patients. To validate our findings and explore the clinical significance of MEX3A, immunohistochemical analysis was conducted on surgical specimens from HCC patients, emphasizing its correlation with factors like hepatitis B virus (HBV) infection status, tumor grade, and tumor dimensions. Additionally, we established HCC cell lines with MEX3A knockdown to delve into its biological roles. Cell proliferation was quantified using both cell counting kit-8 and clone formation assays, while flow cytometry was employed to analyze cell cycle progression. Western blotting and immunofluorescence were utilized to investigate the impact of MEX3A on the Wnt/β-catenin signaling pathway. Moreover, we assessed cell migration through scratch and Transwell assays. Lastly, to gain insights into the role of the transcription factor RORA in modulating MEX3A effects, they silenced RORA and examined its consequences on cellular proliferation and protein expression levels[8].

Analysis of TCGA data revealed that MEX3A mRNA expression levels are significantly elevated in HCC tissues compared to adjacent non-tumor tissues, linked to poorer OS. Immunohistochemistry in HCC specimens confirmed this, also correlated with Ki-67 and vimentin. MEX3A levels were tied to the presence of HBV, tumor grade, and tumor dimensions. Knockdown studies revealed that MEX3A suppresses cell proliferation, arrests cell cycle advancement, and inhibits β-catenin nuclear entry to suppress oncogenic pathways. MEX3A depletion reduced HCC cell migration, possibly via epithelial-mesenchymal transition (EMT) downregulation. RORA was identified as a potential mediator of MEX3A effects, with RORA silencing reversing MEX3A's impact on cell proliferation and β-catenin pathway proteins. Liu’s lab is one of the earliest to work on TCGA biomarker studies, and they developed different strategies in TCGA biomarker studies[9-14]. While the TCGA cohort analysis is robust, the clinical validation (26 HCC specimens) is relatively small. Expanding the cohort in future studies could enhance statistical power and validate associations with HBV status and differentiation. Although RORA is implicated in MEX3A-mediated β-catenin regulation, the exact mechanism by which MEX3A modulates RORA remains unclear. As MEX3A is an RNA-binding protein, post-transcriptional regulation (e.g., mRNA stability or translation) warrants exploration. The study shows that MEX3A regulates EMT but not through RORA. Recent studies have highlighted advancements in liquid biopsies for cancer diagnostics and monitoring[15]. Additional pathways (e.g., PI3K/AKT or Notch) might contribute to MEX3A-driven migration, which could be addressed in follow-up work.

Future perspective

The precise role of human MEX-3 proteins in tumorigenesis remains largely undefined and requires more detailed investigation with potential future studies in drug resistance target discovery, such as CRISPR screening[16]. Across numerous tumor tissues, MEX-3 homologs are frequently overexpressed compared to corresponding normal tissues, although there are notable exceptions. According to several studies, members of the MEX-3 family exhibit heterogeneous expression patterns across different tumor types, as illustrated by the human protein atlas[17-19]. Specifically, MEX-3A-C exhibits heightened expression across testicular, endometrial, breast, ovarian, and brain malignancies, while MEX-3D was not upregulated in tumors. Furthermore, beyond TCGA data, research has reported elevated MEX-3A mRNA levels in human bladder cancer tissues relative to adjacent non-cancerous counterparts, suggesting a potential involvement of human MEX-3A in the progression and metastasis of bladder cancer[20]. Furthermore, elevated levels of MEX-3A have been observed in liver cancer, which significantly correlates with poor patient survival outcomes[21]. Regarding the functional significance of MEX-3A expression, its downregulation in several cancer cell lines resulted in decreased cellular proliferation, migration, and tumorigenic potential. These findings indicate that MEX-3A is implicated in the onset and progression of both gastric and liver cancers, and it may potentially emerge as a novel and promising therapeutic target for the treatment of these malignancies. Future studies should validate these findings in patient-derived xenograft models[22].

In conclusion, Ji et al[8] made a significant contribution to HCC research by delineating MEX3A’s oncogenic role. Their findings open new avenues for prognosis and therapy. We eagerly anticipate further studies to translate these insights into clinical practice.