UV induced DNA damage and transcriptional regulation of alternative splicing

MANUEL J. MUÑOZ

Milan

Seminario; IFOM-IEO; 2012

IFOM-IEO

UV irradiation, DNA damage and Alternative Splicing Manuel J. Muñoz Laboratorio de Fisiología y Biología Molecular, FCEN and IFIBYNE, UBA-CONICET, Buenos Aires, Argentina. DNA is the only biopolymer that is neither disposable nor recyclable, and therefore must be repaired when damaged. DNA damage, caused endogenously or by gamma rays, UV irradiation and various environmental genotoxic compounds, triggers specific intracellular signal cascades, lesion repair mechanisms and gene regulatory events that may result in mutation reversion or spreading, cell cycle arrest, senescence or apoptosis. Transcriptional regulation and alternative pre-mRNA splicing have been identified as crucial targets of signal cascades triggered by DNA damage. We have previously shown that UV irradiation (UVC, 254 nm) causes the hyperphosphorylation of the carboxy terminal domain (CTD) of RNA polymerase II (pol II) large subunit, which slows transcriptional elongation rate and affects alternative splicing of a subset of genes through the kinetic coupling of transcription and splicing. UV mutagenesis is a critical step in the generation of different forms of skin cancer, which develops almost exclusively in sun exposed areas. Since UVC radiation is fully filtered by the ozone layer, we extend our studies to UVB light (305nm), the most harmful radiation from the Sun that reaches the Earth?s surface. Consistent with our model, we found that UVB irradiation of human keratinocytes in culture affects CTD hyperphosphorylation being this modification necessary for the observed change in AS of a model cassette exon. Moreover, UVB irradiation induces the pro-apoptotic mRNA isoforms of Bcl-x and C9 being these results consistent with a key role of AS in skin response to DNA damage. Finally, while UVC and UVB light causes the same types of mutagenic DNA lesions, cyclobutane pyrimidine dimers (CPD) and (6-4)photo-products (64PP), the relative distribution of these lesions are different since UVB irradiation provoke less 64PPs than UVC. Moreover, preliminary data suggests that the nucleosome protects DNA from CPD formation but even more for 64PP induction. Transcriptome analysis of UVC or UVB treated keratinocytes might shed light on specific CPD or 64PP response pathways.