Tumorigenic conversion of immortal human skin keratinocytes (HaCaT) by elevated temperature

UV-radiation is a major risk factor for non-melanoma skin cancer causing sp ecific mutations in the p53 tumor suppressor gene and other genetic aberrat ions. We here propose that elevated temperature, as found in sunburn areas, may contribute to skin carcinogenesis as well. Continuous exposure of immo rtal human HaCaT skin keratinocytes (possessing UV-type p53 mutations) to 4 0-C reproducibly resulted in tumorigenic conversion and tumorigenicity was stably maintained after recultivation of the tumors. Growth at 40 degrees C was correlated with the appearance of PARP, an enzyme activated by DNA str and breaks and the level corresponded to that seen after 5 Gy gamma-radiati on. Concomitantly, comparative genomic hybridization (CGH) analyis demonstr ated that chromosomal gains and losses a;ere present in cells maintained at 40 degrees C while largely absent at 37 degrees C, Besides individual chro mosomal aberrations, all tumor-derived cells showed gain of chromosomal mat erial on. 11q with the smallest common region being 11q13.2 to q14.1. Cycli n DI, a candidate gene of that region was overexpressed in all tumor-derive d cells but cyclinD1/cdk4/cdk6 kinase activity was not increased. Thus, the se data demonstrate that long-term thermal stress is a potential carcinogen ic factor in this relevant skin cancer model, mediating its effect through induction of genetic instability which results in selection of tumorigenic cells characterized by gain of 11q.