Phenotypic plasticity of pheochromocytoma and normal adrenal medullary cells

Much of the phenotypic plasticity exhibited by pheochromocytoma cells is shown by normal immature chromaffin cells. Considerable plasticity is also retained by human adrenal medullary cells and probably by adrenal medullary cells of other species in adult life. Many of the cells which exhibit this plasticity have or acquire characteristics of SIF cells. There are a number of unexplained differences among pheochromocytoma, immature and adult chromaffin cells in vivo and in vitro, particularly with regard to NGF requirements for cell survival and maintenance of processes, the role of endogenous NGF-like substances in promoting neurite outgrowth, glucocorticoid modulation of NGF responsiveness, and selective enzyme induction by NGF and steroids. Continued parallel studies of pheochromocytoma lines and normal chromaffin cells might help to clarify morphological and functional interrelationships within and between classes of sympathetic cells, and to elucidate mechanisms which regulate growth and phenotypic expression in these cells in normal and neoplastic states.