A ROLE FOR EPIDERMAL GROWTH-FACTOR RECEPTOR, C-SRC AND FOCAL ADHESIONKINASE IN AN IN-VITRO MODEL FOR THE PROGRESSION OF COLON-CANCER

We have examined the function of the epidermal growth factor (EGF) rec eptor, c-Src and focal adhesion kinase (FAK) in the progression of col on cancer using an in vitro progression model. A non-tumorigenic cell line was derived from a premalignant colonic adenoma (PC/AA) from whic h a clonogenic variant was established (AA/C1). Following sequential t reatment with sodium butyrate and the carcinogen N-methyl-N'-nitro-N-n itrosoguanidine an anchorage-independent line was isolated which, with time in culture, became tumorigenic when injected into athymic nude m ice (AA/C1/SB10). We have shown that both EGF receptor and FAK protein levels were elevated in the carcinoma cells as compared to the adenom a cells, while the expression and activity of c-Src were unaltered dur ing the adenoma to carcinoma transition. EGP induced the movement of t he carcinoma cells into a reconstituted basement membrane which was no t seen with the premalignant adenoma cells. This increased motility wa s accompanied by an EGF-induced increase in c-Src kinase activity, rel ocalisation of c-Src to the cell periphery and phosphorylation of FAK in the carcinoma cells but not in the adenoma cells. This suggests tha t c-Src plays a role in the biological behaviour of colonic carcinoma cells induced by migratory factors such as EGF, perhaps acting in conj unction with FAK to regulate focal adhesion turnover and tumour cell m otility. Furthermore, although c-Src has been implicated in colonic tu mour progression, we demonstrate here that in the adenoma to carcinoma in vitro model c-Src is not the driving force for this progression bu t co-operates with other molecules in carcinoma development.