RNA-binding protein PTBP1 mediates HSV-1 infection through splicing regulation of HS 3-O-sulfotransferase genes

Polypyrimidine tract-binding protein 1 (PTBP1) is an RNA-binding protein (RBP) that plays an instrumental role in regulating alternative splicing events by manipulating RNA folding. Here we report a novel role of PTBP1 in heparan sulfate (HS) biosynthesis. Specifically, we found that genetic ablation of PTBP1 resulted in loss of HS3ST3A1 and HS3ST3B1 (also known as 3OST3A1 and 3OST3B1, respectively) expression. Both the HS3ST3A1 and HS3ST3B1 genes, which encode heparan sulfate -glucosamine 3-O-sulfotransferases for heparan sulfate modification of proteoglycans (HSPGs), are unique in that each pre-mRNA is composed of 2 exons separated by an extraordinarily long intron. Analyses of global iCLIP-seq and CRIC-seq revealed that the intron region of HS3ST3A1/HS3ST3B1 pre-mRNAs interacted with the PTBP1 dimer, creating contacts to impact splicing events. Ectopic expression of WT, but not a dimerization defective mutant (C23S) of PTBP1, restored functional 3OST3 expression. Cell-surface HSPGs are the most abundant proteoglycans that can act as co-receptors modulating cytokine activities as well as for viruses to attach and to enter cells. We showed that loss of 3OST3 expression markedly reduced HSV-1 infection and viral spreading. This study demonstrates that PTBP1 mediates 3OST3 expression for HS biosynthesis and plays a role in HSV-1 infection.