Properties of an epithelial cell type in culture: the epidermal keratinocyte and its dependence on products of the fibroblast.

Keratinocytes of stratified squamous epithelium can be grown serially in culture and retain the various markers typical of their form of differentiation. In order to form colonies at each transfer, the keratinocytes must be suitably supported by fibroblasts. Established keratinocyte lines of teratomal origin show this dependence, as do diploid strains of finite culture life derived from human skin. For at least some keratinocyte lines, this requirement can be satisfied by soluble products elaborated by the fibroblasts. It is suggested that epithelial cells in general may not be independent cell types and that their poor cultivability may be due to failure to provide suitable fibroblast support. The existence of a number of established lines of epithelial origin that can grow without such support and of lines of fibroblastic origin which cannot support keratinocytes suggests that both epithelial dependence and the fibroblast supporting function can sometimes be lost in established cell lines.