L'influence de la proteine p53 sur la reponse genotoxique des cellules humaines aux ultraviolets (French text)

Inactivation of the p53 regulatory pathway is a major early event in the initiation of solar UV-induced melanoma skin cancer. However, investigations on the cellular response to sunlight have yielded important contradictions in the literature due to (1) the use of different experimental strategies to abrogate or reduce p53 activity in cultured cells, e.g. p53 knockouts (genetic inactivation) vs. expression of viral oncoproteins or dominant-negative mutants (functional inactivation) and (2) the use of different incident UV wavelengths, i.e., sources producing either monochromatic 254nm UV vs UVB (290–320).; This thesis, in a very substantial manner, addresses the basis for these contradictions by rigorously comparing critical cellular responses (i.e. clonogenic survival, mutation frequency at the HPRT locus, extent of DNA repair at the HPRT and c-jun locus, apoptotic response and kinetic of G1-S progression) to different regions of the UV wavelength spectrum, using an isogenic human cell culture system composed of the human lymphoblastoid cell line TK6 and two isogenic derivatives, i.e. TK6-5E, in which p53 is inactivated functionally by expression of the HPVE6 oncoprotein and NH32 arboring a genetic inactivation of p53.; We were able to demonstrate that p53 plays an essential role in transcription-coupled nucleotide excision repair following UVB but not after 254nm UV treatment. Furthermore, we were able to show that functional inactivation of p53 by HPVE6 expression does not faithfully reproduce the genetic inactivation of p53 for either clonogenic survival, mutation frequency at the HPRT locus, apoptosis or G1-S progression.; This work emphasizes the important differences in the response of human cells to the different regions of the ultraviolet spectrum and unravels how p53 protects against the harmful effects of ultraviolet light.