Oncogenic Potential of the Dual-Function Protein MEX3A

SIMPLE SUMMARY: RNA-binding proteins (RBPs) are involved in the post-transcriptional control of gene expression, modulating the splicing, turnover, subcellular sorting and translation of (m)RNAs. Dysregulation of RBPs, for instance, by deregulated expression in cancer, disturbs key cellular processes such as proliferation, cell cycle progression or migration. Accordingly, RBPs contribute to tumorigenesis. Members of the human MEX3 protein family harbor RNA-binding capacity and E3 ligase activity. Thus, they presumably combine post-transcriptional and post-translational regulatory mechanisms. In this review, we discuss recent studies to emphasize emerging evidence for a pivotal role of the MEX3 protein family, in particular MEX3A, in human cancer. ABSTRACT: MEX3A belongs to the MEX3 (Muscle EXcess) protein family consisting of four members (MEX3A-D) in humans. Characteristic for MEX3 proteins is their domain structure with 2 HNRNPK homology (KH) domains mediating RNA binding and a C-terminal really interesting new gene (RING) domain that harbors E3 ligase function. In agreement with their domain composition, MEX3 proteins were reported to modulate both RNA fate and protein ubiquitination. MEX3 paralogs exhibit an oncofetal expression pattern, they are severely downregulated postnatally, and re-expression is observed in various malignancies. Enforced expression of MEX3 proteins in various cancers correlates with poor prognosis, emphasizing their oncogenic potential. The latter is supported by MEX3A’s impact on proliferation, self-renewal as well as migration of tumor cells in vitro and tumor growth in xenograft studies.