DNA Damage controls alternative splicing through its coupling with transcription

M.J. MUÑOZ AND A.R. KORNBLIHTT

Campana, Buenos Aires, Argentina

Congreso; Biology in Balance; 2009

Massachusetts General Hospital and IPSEN

Alternative splicing (AS) affects the expression of 65% of human genes, generates high protein diversity and is implicated in human disease. The rate of transcription elongation determines the outcome of two competing splicing reactions that occur co-transcriptionally. Rapid transcription favors exon skipping, whereas slower transcription favors exon inclusion. Many apoptotic genes are regulated via alternative splicing (AS) but little is known about the control mechanisms derived from DNA damage. Here we show that ultraviolet (UV) radiation affects co-transcriptional AS in a p53-independent way, through the hyperphosphorylation of RNA polymerase II carboxy terminal domain (CTD) and a subsequent and unprecedented inhibition of transcriptional elongation, estimated in vivo and in real time by FRAP. Phopshomimetic CTD mutants not only display lower elongation but duplicate the UV effect on AS. Consistently, nonphosphorylatable mutants prevent the UV effect. Confirming the relevance of this mechanism, apoptosis promoted by UV light in cells lacking p53 is prevented when the change in AS of the apoptotic gene Bcl-x is reverted. Using splicing-sensitive microarrays, we found a significant overlap of the subsets of genes changing AS with UV light and those that also downregulate their expression, suggesting that transcription/AS coupling is a key feature of the DNA damage response.