Conférence Manuel J. MUNOZ, Dr FCEN and IFIBYNE, Argentina PDF Imprimer Envoyer
Vendredi, 09 Novembre 2012 16:30
Conférence Manuel J. MUNOZ, Dr FCEN and IFIBYNE, Argentina

UV irradiation, DNA damage and alternative splicing

Laboratorio de Fisiologia y Biologia Molecular
Buenos Aires, Argentina

Lundi 12 novembre 2012

Amphi 2 - Faculté de Médecine, 22 av. Camille Desmoulins - Brest

UV irradiation, DNA damage and alternative splicing

DNA is the only biopolymer that is neither disposable nor recyclable, and therefore must be repaired when damaged. DNA damage, caused endogenously or by 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 though the relative contribution to the transcriptional/DNA damage response of the most conspicuous UV-induced DNA lesions i.e., cyclobutane pyrimidine dimers (CPD) and 6-4 pyrimidone photoproducts (6-4 PP), is unclear. It has been recently shown that UVB radiation (302 nm), which is the most harmful solar radiation that reaches the Earth’s surface, induces higher CPD/6-4 PP ratios than UVC. Although both lesions are removed by NER (Nucleotide Excision Repair), the different half-life of a CPD (≈24 hs) and a 6-4 PP (≈2 hs) suggest that the recognition of both lesions, and may be the signaling generated thereafter, are not the same.

To better understand the mechanism by which UV irradiation affects the transcriptional and AS machinery, we have compared the response of human keratinocytes in culture to UVC and UVB treatment using doses that generate comparable CPD amounts. RNA-seq global analysis of control, UVC- and UVB-treated cells revealed that transcriptional down-regulation and higher exon inclusion are more frequent than transcriptional upregulation and exon skipping upon both types of irradiation. However and most interestingly, hundreds of genes are specifically affected by either UVC or UVB, which might reflect specific CPD or 6-4 PP response pathways.

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