ATM and ATR Pathways Signal Alternative Splicing of Drosophila TAF1 Pre-mRNA in Response to DNA Damage

Alternativepre-mRNA splicing is a major mechanism utilized by eukaryotic organismsto expand their protein-coding capacity. To examine the role of cellsignaling in regulating alternative splicing, we analyzed the splicingof theDrosophila melanogaster TAF1 pre-mRNA.TAF1 encodes a subunit of TFIID, which is broadly required for RNApolymerase II transcription. We demonstrate thatTAF1 alternative splicing generates four mRNAs,TAF1-1 ,TAF1-2 ,TAF1-3 , andTAF1-4 , of whichTAF1-2 andTAF1-4 encode proteins that directly bind DNA throughAT hooks.TAF1 alternative splicing was regulated in atissue-specific manner and in response to DNA damage induced byionizing radiation or camptothecin. Pharmacological inhibitors and RNAinterference were used to demonstrate that ionizing-radiation-inducedupregulation ofTAF1-3 andTAF1-4 splicing in S2 cells was mediated by the ATM (ataxia-telangiectasiamutated) DNA damage response kinase and checkpoint kinase 2 (CHK2), aknown ATM substrate. Similarly, camptothecin-induced upregulation ofTAF1-3 andTAF1-4 splicing wasmediated by ATR (ATM-RAD3 related) and CHK1. These findings suggestthat inducibleTAF1 alternative splicing is a mechanism toregulate transcription in response to developmental or DNA damagesignals and provide the first evidence that the ATM/CHK2 and ATR/CHK1signaling pathways control gene expression by regulating alternativesplicing.