Intestinal stem cell marker MEX3A regulates PPARγ expression with functional impact in colorectal carcinogenesis

RNA-binding proteins (RBPs) are major effectors of post-transcriptional regulation. Recently, we described the role of MEX3A in maintaining intestinal stem cell identity and epithelial renewal by repressing the PPAR{gamma} pathway. This work aimed to study MEX3A functional impact in colorectal cancer (CRC). MEX3A and PPAR{gamma} expression profiles were characterized in murine and human models. CRISPR/Cas9-mediated MEX3A knockout was performed in patient-derived CRC tumoroids (PDCTs) and MEX3A RNA targets identified through the HyperTRIBE technique. Apc+/fl;Mex3a+/- mice presented a significant reduction in tumor burden. Apc+/fl;Kras+/G12D;Mex3a+/-mice presented a reduced tumor area, while corresponding tumoroids exhibited reduced growth and enhanced differentiation potential mediated by PPAR{gamma} signalling. MEX3A overexpression (85% of human CRC cases) was inversely correlated with PPAR{gamma} downregulation (72% of cases). Accordingly, MEX3A-depleted PDCTs showed decreased LGR5 expression, accompanied by increased PPAR{gamma} expression and higher sensitivity to 5-Fluorouracil/Oxaliplatin (FOLFOX)-based chemotherapy. The HyperTRIBE results revealed a direct interaction between MEX3A and PPARG transcripts. STATEMENT OF SIGNIFICANCEThese results emphasize that MEX3A plays a crucial role in colorectal carcinogenesis, partially through regulation of the PPARG pathway, mediating tumour development and response to therapy, thus constituting a potential therapeutic target.