Attenuation of genotoxicity under adhesion-restrictive conditions in human metastatic melanoma through modulation of p53, gamma- H2AX and nuclear DNA organization Free

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Introduction. Interactions between tumor cells and their substratum can influence cancer progression by modulating signalling responses to DNA damage such as persistent phosphorylation of histone H2AX (χ-H2AX) together with induction and binding of the tumor suppressor p53 protein to its DNA consensus sequence . Since genotoxic agents like UV irradiation are important in melanoma progression ,we now investigated whether genomic organization, activation of p53 and χ-H2AX are unequally regulated on adhesion-permissive or restrictive substrates . Methods -restrictive substrates diminished spreading and proliferation of neo 6.3/C8161 melanoma in which metastasis is suppressed by introduction of neo-tagged chromosome 6 , but permited proliferation of human metastatic C8161 melanoma (Strasberg Rieber M. et al, Biochem Biophys Res Commun. 2001 ;281:159-5) . Changes in χ-H2AX and DNA organization in chromatin were quantitated by laser scanning cytometry.

Results.-Apoptosis-associated PARP cleavage and DNA fragmentation induced by UV irrradiation were diminished on the restrictive substrate in C8161 melanoma .Increases in the phosphorylation of histone H2AX ,induction of the tumor suppressor p53 protein and greater binding of this protein to its DNA consensus sequence , were all decreased on the restrictive substrate. The latter also promoted a 2 fold increase of DNA condensation in chromatin and enhanced activation of the survival - and invasion associated MMP-9 gelatinase B , in metastatic C81261 melanoma.

Conclusions.- .Our data suggest that adaptation to restrictive substrates in metastatic C8161 melanoma decreases apoptotic susceptibility , partly through attenuation of DNA damage signaling responses and decreased genomic accessibility. These may be some of the mechanisms that attenuate genotoxic damage under restrictive conditions , which may occur when invasive tumor cells try to avert apoptosis during the migratory stages of metastasis.