Relationship between the expression of differentiation-specific keratins 1 and 10 and cell proliferation in epidermal tumors.

In normal epidermis, the expression of keratins 1 and 10 is associated with the loss of proliferative capacity and the onset of terminal differentiation. Keratins 1 (K1) and 10 (K10) are commonly expressed in the differentiating layer of benign tumors, but are lost during progression from the benign to the malignant state in skin carcinogenesis. Active gene constructs of mouse K1 and K10 were introduced into papilloma and carcinoma cell lines derived from keratinocytes to analyze the consequences of the expression of these keratins on the organization of the endogenous cytoskeletal network and on the mitotic activity of the recipient cells. Exogenous K1 integrated into the preexisting keratin K5/K14 network of both SLC-1 carcinoma and 308 papilloma cells. The formation of a recombinant cytoskeleton was more restricted for K10 than for K1 and appeared to be related to a requirement for cessation of cell division before K10 could integrate. The integration of exogenous K1 filaments into the endogenous keratin network was compatible with sustained proliferation of SLC-1 carcinoma cells in vitro. However, the exogenous gene was not expressed in tumor grafts in vivo. In contrast, stable K1 or K10 transfectants could not be selected in 308 cells, suggesting that benign tumor cells expressing suprabasal keratins cannot sustain proliferation.