Prolactin stimulates proliferation of cultured human keratinocytes

The effect of the pituitary hormone prolactin on in vitro proliferation of human keratinocytes has been studied. Cell proliferation was determined by [3H] thymidine incorporation and cell enumeration in culture. Physiologic concentrations of prolactin markedly stimulated proliferation of newborn foreskin keratinocytes in serum-free medium. In addition, it was able to replace almost completely the growth-promoting effects of bovine pituitary extract, a commonly added supplement for keratinocyte culture. This activity was also evident in the absence of epidermal growth factor, but required the presence of insulin. Radioligand-binding studies confirmed the expression of specific prolactin binding sites (Kd 8.9 nM; 1350 sites per cell) on freshly procured keratinocyte membranes. These results extend its hormonal influences to include regulation of in vitro proliferation of human keratinocytes, and suggest the possibility of a completely defined growth medium for keratinocytes.