PTBP1/HNRNP I controls intestinal epithelial cell regeneration by maintaining stem cell survival and stemness
Properly controlled intestinal epithelial cell regeneration is not only vital for protection against insults from environmental hazards but also crucial for preventing intestinal cancer. Intestinal stem cells located in the crypt region provide the driving force for epithelial regeneration, and thus their survival and death must be precisely regulated. We show here that polypyrimidine tract binding protein 1 (PTBP1, also called heterogeneous nuclear ribonucleoprotein I, or HNRNP I), an RNA-binding protein that post-transcriptionally regulates gene expression, is critical for intestinal stem cell survival and stemness. Mechanistically, we show that PTBP1 inhibits the expression of PHLDA3, an AKT repressor, and thereby maintains AKT activity in the intestinal stem cell compartment to promote stem cell survival and proliferation. Furthermore, we show that PTBP1 inhibits the expression of PTBP2, a paralog of PTBP1 that is known to induce neuron differentiation, through repressing inclusion of alternative exon 10 to Ptbp2 transcript. Loss of PTBP1 results in a significant upregulation of PTBP2, which is accompanied by splicing changes in genes that are important for neuronal cell development. This finding suggests that PTBP1 prevents aberrant differentiation of intestinal stem cells into neuronal cells through inhibiting PTBP2. Our results thus reveal a novel mechanism whereby PTBP1 maintains intestinal stem cell survival and stemness through the control of gene function post-transcriptionally.