Insulin binding properties of normal and transformed human epidermal cultured keratinocytes

Insulin binding to its receptors was studied in cultured normal and transformed (A431 line) human epidermal keratinocytes. The specific binding was a temperature-dependent, saturable process. Normal keratinocytes possess a mean value of about 80,000 receptors per cell. Fifteen hours exposure of the cells to insulin (2 X 10(-7) M) lowered their receptor number (about 65% loss in available sites); these reappeared when the hormone was removed from the culture medium ("down-regulation" process). In the A431 epidermoid carcinoma cell line, there is a net decrease in insulin binding (84% of the initial bound/free hormone ratio in comparison with normal cells) essentially related to a loss in receptor affinity for insulin. Thus, cultured human keratinocytes which express insulin receptors may be a useful tool in understanding skin pathology related to insulin disorders.