A5 - Molecular and structural dynamics of bimodal mRNA expression regulation by the embryonic stem cell differentiation and cancer checkpoint protein TRIM71

TRIM71 (also known as Lin-41) is an ancient stem cell regulator conserved in the developmental programs of both invertebrates and vertebrates. The stem cell protein was first described as being required for proper differentiation timing during C. elegans embryogenesis but has since then been determined to safeguard embryonic development in all animal models tested, including Drosophila, zebrafish, and mice. Recently, TRIM71 has also been implicated in human diseases such as infertility and cancer, and most recently it has been identified as the predominantly mutated gene in the so-called human congenital hydrocephalus, a frequent abnormality in the brain development of newborns. Moreover, recent evidence points to the fact that one of the key mechanisms exerted by TRIM71 in stem cells and cancer cells is its ability to control the expression of cellular mRNA targets, such as stem cell differentiation/proliferation checkpoint proteins, e.g., p21. Cellular mRNA targets of TRIM71 in mammals are characterized by long 3’UTRs, and we were able to show that one important mechanism in degrading such targets involves the so-called Nonsense-Mediated Decay (NMD)-machinery, normally used for discarding “faulty” mRNAs which contain premature stop-codons. However, recent evidence shows that TRIM71 controls cellular mRNAs at various levels, which includes inhibition of translation, or even the reverse stabilization of some of its targets. This project aims at the identification and characterization of the dynamic and context-specific interactions of TRIM71 with cell-fate decision-making machinery that jointly assembles on target mRNAs. This will involve specific, aptamer-driven target mRNA pull-down from cells, identification of the associated proteomes, and mapping out TRIM71-dependent protein-protein, as well as protein-nucleic acid interactions in detail. A second line of research will aim at the identification of RNA aptamers that bind to the NHL domains of TRIM71 with high affinity, and to utilize these novel tools, e.g., as innovative aptamer inhibitors in stem cell and cancer cell biology.