CDX2 regulation by the RNA-binding protein MEX3A: impact on intestinal differentiation and stemness

Abstract

The homeobox transcription factor CDX2 plays a crucial role in intestinal cell fate specification, both during normal development and in tumorigenic processes involving intestinal reprogramming. The CDX2 regulatory network is intricate, but it has not yet been fully uncovered. Through genome-wide screening of a 3D culture system, the RNA-binding protein MEX3A was identified as putatively involved in CDX2 regulation; therefore, its biological relevance was addressed by setting up cell-based assays together with expression studies in murine intestine. We demonstrate here that MEX3A has a repressive function by controlling CDX2 levels in gastric and colorectal cellular models. This is dependent on the interaction with a specific binding determinant present in CDX2 mRNA 3′untranslated region. We have further determined that MEX3A impairs intestinal differentiation and cellular polarization, affects cell cycle progression and promotes increased expression of intestinal stem cell markers, namely LGR5, BMI1 and MSI1. Finally, we show that MEX3A is expressed in mouse intestine, supporting an in vivo context for interaction with CDX2 and modulation of stem cell properties. Therefore, we describe a novel CDX2 post-transcriptional regulatory mechanism, through the RNA-binding protein MEX3A, with a major impact in intestinal differentiation, polarity and stemness, likely contributing to intestinal homeostasis and carcinogenesis.

RNA‐seq of the aging brain in the short‐lived fish N. furzeri – conserved pathways and novel genes associated with neurogenesis

“…Some of the identified genes are of unknown function in the nervous system. MEX3A codes for an RNA-binding protein that, in intestinal cells, regulates MSI1 (Pereira et al ., 2013), a neurogenic gene expressed in N. furzeri NSCs (Terzibasi Tozzini et al ., 2012). ZNF367 and KRCP are putative transcription factors that act as central nodes in gene coregulation networks, and their function in the nervous system is unknown.…”

The RNA binding protein MEX-3 retains asymmetric activity in the early Caenorhabditis elegans embryo in the absence of asymmetric protein localization

“…In a cellular model for developing intestinal epithelium, ectopic MEX3A leads to an increase in the proportion of S phase cells, an increase in the expression of intestinal stem cell markers, and perturbation of apical-basal identity (Pereira et al, 2013). These changes coincide with a reduction in CDX2 protein but not Cdx2 mRNA in the cells prior to confluence, and are consistent with the observed expression of endogenous MEX3A at the base of the intestinal epithelial folds (Pereira et al, 2013), where stem cells reside and continually divide to replace differentiated intestinal cells (Casali and Batlle, 2009). Knockdown of Mex3a by RNAi in three human gastric cancer cell lines inhibited cell proliferation, reduced the proportion of cells in S phase, reduced anchorage-independent growth, and suppressed cell migration (Jiang et al, 2012).…”

“…Intriguingly, caudal in the flour beetle Tribolium is repressed by a mex-3 homolog and by a protein sharing similarity with Bicoid (Schoppmeier et al, 2009). Furthermore, mammalian MEX3A has been shown to bind the Cdx2 3′UTR and reduce CDX2 protein levels in cell culture (Pereira et al, 2013).…”

Mex3a Marks a Slowly Dividing Subpopulation of Lgr5+ Intestinal Stem Cells

“…Mex3 proteins have highly conserved RNA binding domains and a C-terminal RING finger domain with E3 ubiquitin ligase activity (Buchet-Poyau et al, 2007). The role of Mex genes in mammals is largely unknown, yet their C. elegans homologue – mex3 -, is required for germline stem cell identity and maintenance (Ciosk et al, 2006) whereas human MEX3A has been correlated to stemness in colon cancer cell lines (Pereira et al, 2013). Here we report that Mex3a labels a subpopulation of slow proliferating progenitor cells located around +3/+4 crypt position.…”