Serum and growth factor requirements for proliferation of human adrenocortical cells in culture: comparison with bovine adrenocortical cells

Although bovine adrenocortical cells proliferate readily in cell culture, proliferation of fetal or adult human adrenocortical cells has been observed to be limited and preparation of pure proliferating cultures of human adrenocortical cells has not been reported. The growth requirements of fetal human definitive zone adrenocortical cells in culture were compared to the established requirements of bovine adrenocortical cells. The medium used was 1:1 Ham's F12 and Dulbecco's modified Eagle's medium supplemented with transferrin and insulin. Earlier experiments showed that human cells had a greater proliferative response to horse serum than to fetal bovine serum, whereas the opposite was true for bovine cells. When plated on fibronectin-coated dishes and exposed to varying concentrations of horse serum in the presence of 100 ng/ml fibroblast growth factor (FGF), increasing cell growth was observed up to a serum concentration of 50%. When 50% fetal bovine serum was used instead of horse serum proliferation was less. In contrast, bovine adrenocortical cells showed a maximal proliferative response to either fetal bovine serum or horse serum at 10%. Human adrenocortical cells thus have a very high requirement for serum; 50% is the highest level that may be practically used, but the shape of the dose-response curve suggests that this concentration is still suboptimal. Growth was less in the absence of FGF. Epidermal growth factor can partially substitute for FGF. No response to 100 nM placental lactogen was observed. Less growth was observed when dishes were not coated with fibronectin. The factors present in horse serum that are evidently needed in high amounts by human cells are unknown. Despite this lack of knowledge, use of 50% horse serum enabled long-term growth of human adrenocortical cells that are pure by the criterion of retraction in response to ACTH. Nonadrenocortical cells do not show a retraction response. Such long-term cultures may be useful in studies of long-term regulation of differentiated function, aging, and carcinogenesis.