U1 snRNP regulates alternative polyadenylation in DNA damage response

The DNA damage response (DDR) involves coordinated control of gene expression and DNA repair. Using deep sequencing we found widespread changes of alternative cleavage and polyadenylation (APA) site usage upon UV-treatment in mammalian cells. APA regulation in the 3’ untranslated region (3’UTR) is substantial, leading to both shortening and lengthening of 3’UTRs. Interestingly, a strong activation of intronic APA sites is detected, resulting in widespread expression of truncated transcripts. Intronic APA events are biased to the 5’ end of genes and affect gene groups with important functions in DDR. Moreover, intronic APA site activation during DDR correlates with a decrease in U1 snRNA levels, and this is reversed by U1 snRNA overexpression. Importantly, U1 snRNA overexpression decreases UV-induced apoptosis. Together, these studies describe a significant gene regulatory scheme in DDR where U1 snRNP impacts gene expression via APA.