iFIT Distinguished Seminars: Exploiting PCBP2-Mediated RNA Regulation to Enhance TCR-Based Immunotherapies
We ran genome-wide and focused CRISPR screens to identify factors that sensitize tumor cells to CD4+ T cell killing. One of our hits was the RNA-binding protein PCBP2 and we found that sensitization of PCBP2-deleted tumor cells is mediated by increased sensitivity to TNF/IFNg-induced apoptosis. We further dissected this mechanistically and found that the PCBP2 KO (P2 KO) phenotype is specifically regulated by P2 isoforms that lack coding exon 8 which sits in the linker region between the RNA-binding domains KH2 and KH3. Intersecting RNA-seq with pan-P2 and isoform-resolved eCLIP data nominated U2AF2 as a candidate target that is regulated in an isoform-specific manner and whose re-expression reverted the P2 KO phenotype. We are actively working on which differential binding event (3’UTR vs poison exon) at the U2AF2 locus drives U2AF2 regulation by PCBP2. In orthotopic in vivo models, we validated that P2 KO sensitizes tumor cells to adoptively transferred tumor-specific CD4+ T cells.
In an independent but related project, we found that P2 also has a T-cell-intrinsic function, regulating a poison exon in LAG3 and thereby regulating LAG3 surface expression in acutely versus chronically stimulated T cells. Building on this observation, we generated an “exhaustion-gated” expression construct that enables localized payload expression within the tumor microenvironment. (1/3rd of the talk)
