SV40-immortalized human keratinocytes as an in vitro model system for studying environmental carcinogens

We have extensively characterized the properties of an in vitro model system of human epidermal keratinocytes immortalized by the oncogenic virus, SV40. Here we show how the unique features of this system can be employed as a tool for studying the effects of both mutagenic and nongenotoxic carcinogens on human epithelial cells. 1. SV40-infected human keratinocyte lines at low serial passage have been used as an in vitro system to study the effects of arsenic. Arsenic as both arsenate and arsenite was found to stimulate cell growth over test periods of 5 and 7 days at submicromolar concentrations. Tyrosine specific phosphorylation was examined in immunoprecipitates from cells exposed to arsenic at growth stimulatory concentrations. A number of phosphorylated species which were found to be present in both arsenite and arsenate treated cells were not observed in the untreated cells. Concomitantly, analyses of cell cycle kinetics by fluorescence activated cell sorting (FACS) revealed that the stimulation of cell growth might be accounted for by a relative shortening of the G1 phase of the cell cycle. 2. The mutagenic effects of the methylating carcinogen, MNNG have been studied using the integrated viral origin of replication in a line of SV40-immortalized human keratinocytes as a target. Sequence data from this system revealed an unusual spectrum of base alterations as compared with data obtained with bacteria and other mammalian cell types including single nucleotide insertions and deletions and base-pair inversions.