TO THE EDITOR
We are writing to comment on the recently published study by Ji et al[1], which explored the role of MEX3A in hepatocellular carcinoma (HCC). HCC represents a significant global health challenge, particularly in Asia, where it is the fifth most prevalent cancer and the second leading cause of cancer-related mortality. HCC accounts for a considerable proportion of liver cancer cases worldwide[2]. Recent advancements in surgical techniques, radiotherapy, targeted therapies, and immunotherapy have led to improved patient prognosis and survival rates. Nevertheless, the complexity and heterogeneity of HCC underscore the necessity for the development of more effective and personalized therapeutic strategies. Consequently, the identification of reliable prognostic biomarkers and therapeutic targets is essential for the early diagnosis and treatment of HCC[3]. MEX3A, a member of the MEX3 family, has been implicated in the progression of various diseases, including cancer. In the context of bladder and ovarian cancers, the expression of MEX3A is significantly elevated in tumor tissues when compared to adjacent non-tumorous tissues[4,5]. Furthermore, the silencing of MEX3A expression has been demonstrated to inhibit the proliferation, migration, and clonal expansion of gastric cancer cells, thereby suggesting its role in tumor progression[6]. In HCC, high expression levels of 13 genes, including MEX3A, have been associated with poor prognosis[7]. Additionally, MEX3A exhibits a high mutation frequency in HCC patients, with its expression markedly increased in individuals at high risk[8]. Although the precise function and underlying mechanisms of MEX3A in HCC remain to be elucidated, these findings underscore its potential as a key molecular target in HCC research. Further investigation into MEX3A may provide novel insights and contribute to the development of innovative diagnostic and therapeutic strategies for HCC.
The study by Ji et al[1] advanced our understanding by showing that MEX3A enhances cell proliferation in HCC through the RORA/β-catenin signaling pathway, underscoring its potential both as a prognostic marker and therapeutic target. The researchers conducted an initial analysis of data from The Cancer Genome Atlas database and discovered that MEX3A mRNA was highly expressed in HCC tissues. Furthermore, patients exhibiting elevated levels of MEX3A expression demonstrated significantly shorter overall survival rates. An analysis of 26 surgical specimens from HCC patients further corroborated the high expression of MEX3A in tumor tissues, and identified a correlation with tumor diameter, degree of differentiation, and hepatitis B virus positivity. These findings indicate that MEX3A may serve as a valuable prognostic biomarker. To further elucidate the functional role of MEX3A, HCC cell lines with MEX3A knockdown were established. The knockdown of MEX3A was observed to inhibit cell proliferation, as evidenced by cell counting kit-8, and colony formation assays. Flow cytometry analysis indicated cell cycle arrest at the G1 phase, while wound healing and Transwell experiment migration assays demonstrated a significant reduction in cell migration. Mechanistic studies further revealed that MEX3A activates the Wnt/β-catenin signaling pathway to promote cellular proliferation, and enhances migration through the epithelial-mesenchymal transition pathway. Furthermore, transcription factor analysis has identified RORA as a downstream target of MEX3A. To investigate this relationship, a dual-knockdown cell model was developed. Experimental results indicated that RORA antagonizes the MEX3A induced activation of both cell proliferation and the Wnt/β-catenin signaling pathway. However, RORA did not appear to affect the regulatory influence of MEX3A on the epithelial-mesenchymal transition pathway. Collectively, these findings suggest that MEX3A enhances HCC cell proliferation through the RORA/β-catenin signaling axis, thereby providing novel insights into its oncogenic role in HCC. However, certain aspects of the study require further examination to comprehensively assess MEX3A’s role in HCC.
The study’s validation cohort comprised only 26 patients and failed to distinguish between subgroups based on etiology (e.g. hepatitis B virus, hepatitis C virus, or nonviral hepatitis) or tumor stages. The limited sample size may lack statistical power to represent the diverse MEX3A expression profiles across the broader HCC population. Future studies should expand the sample size and include participants from multiple centers to enhance the statistical robustness and account for the heterogeneity in patient demographics, disease stages, and treatment histories. In addition, although the study suggests MEX3A regulates RORA expression, it does not clarify the mechanism of action. In other cancer studies, such as Bufalieri et al[9] on glioblastoma, the interactions between MEX3A and its target proteins, such as retinoic acid-inducible gene I, were meticulously detailed, uncovering novel molecular mechanisms. Similar in-depth investigations are necessary to elucidate how MEX3A influences RORA in HCC.
We propose several new research directions to further investigate the role of MEX3A in HCC. Firstly, studying the relationship between MEX3A and the HCC immune microenvironment is vital. This microenvironment is crucial in the development and progression of HCC, with immune cells known to both promote and inhibit tumor growth[10]. Given MEX3A’s documented immune-related function in cancer[11,12], analyzing the composition and function of immune cells in MEX3A-overexpressing tumors is essential. Single-cell RNA sequencing can be employed to analyze the composition of immune cells, while immunohistochemistry facilitates the detection of immune-related protein expression and elucidates the distribution of diverse immune cells within tissues. Flow cytometry enables precise determination of the proportions and functional status of various immune cell types. Zhang et al[12] found a negative correlation between MEX3A expression and immune cell infiltration in ovarian cancer. Similar analyses in HCC could elucidate how MEX3A affects immune cell recruitment, activation and function in the tumor microenvironment. Testing the impact of MEX3A knockdown on immunotherapy outcomes in HCC is also crucial. Although immunotherapy is a promising treatment for HCC, its efficacy remains limited for many patients. By knocking down MEX3A in a preclinical model, we can determine if it enhances tumor sensitivity to immunotherapy, and will involve assessments of immune cell infiltration, activation of immune-related signaling pathways, and expression of immune checkpoint molecules. For example, Lin et al[11] demonstrated that MEX3A expression was closely linked with immune infiltration in soft tissue sarcoma, suggesting that modulating MEX3A expression could be a novel strategy to improve immunotherapy effectiveness in HCC patients. Hu et al[7] established that MEX3A, a gene utilized in the development of gene signatures, correlates with immune microenvironment characteristics in HCC, encompassing hypoxia, immune checkpoint expression, and immune cell infiltration. Their findings indicate that hypoxia and immune-related prognostic signatures involving MEX3A may function as a potential approach for HCC risk stratification. Wang et al[13] indicated that the expression, methylation, and mutation status of MEX3A are intricately associated with the HCC immune microenvironment, thereby underscoring its potential significance in tumor immunity and progression.
Secondly, it is vital to explore the relationship between MEX3A and cancer stem cells (CSCs) in HCC. CSCs, defined as subpopulations of cancer cells capable of self-renewal and tumor initiation, contribute to tumor recurrence and therapy resistance[14-16]. Evaluating the effect of MEX3A on CSC self-renewal is essential for grasping its role in HCC progression. A study addressed the importance of CSC-specific markers and signaling pathways in driving tumor growth[16]. MEX3A might interact with these pathways, potentially affecting the Wnt/β-catenin pathway, which plays a key role in CSC self-renewal. By using in vitro and in vivo models, such as sphere formation assays and xenograft assays, we can determine whether MEX3A promotes or inhibits CSC self-renewal. This information could lead to the development of targeted therapies that specifically block MEX3A-mediated CSC self-renewal, thereby reducing tumor recurrence risks. Organoids are excellent for predicting therapeutic drug responses, showing concordance in drug response determination with patient-derived xenograft models and corresponding primary tumors[17]. To evaluate the targeting ability of MEX3A inhibitors, we can utilize HCC organoids, which mimic the structural and cellular heterogeneity of tumors. Treating these organoids with MEX3A inhibitors allows us to assess their impact on the cells within the organoids that may have characteristics related to CSCs, providing insights into the potential of MEX3A inhibitors to target CSCs and reduce tumor-forming capacity.
