| Abstract: | Human teratocarcinoma cells in culture offer an in vitro system for studying certain aspects of embryonic differentiation. To gain some insight into regulatory systems that might be operative during early human development, we have characterized the alterations that occur in the hormonal responsiveness of human embryonal carcinoma cell adenylate cyclase with differentiation in response to 10 microM retinoic acid. Two cell lines CL12 and CL13, cloned from Tera 2 cells by Dr. C. F. Graham, have been used in these studies. Adenylate cyclase of CL12 and CL13 cells is stimulated in the presence of 10 microM GTP by epinephrine and calcitonin, with calcitonin being the most potent stimulator of cyclic AMP production. Exposure of these cells to retinoic acid leads to an arrest in growth and within 6 days to a differentiated cell population with a stable nonreversible phenotype. No changes in basal, GTP- and fluoride-stimulated adenylate cyclase activities are observed with retinoic acid treatment, but the cyclase of differentiated cells exhibits a greater stimulation by calcitonin (7.5-fold) and the appearance of a somatostatin inhibitory effect. Somatostatin specifically inhibits, by 25%, the hormonal stimulation of adenylate cyclase of cells treated for 5 days with retinoic acid. The increase in calcitonin stimulation of adenylate cyclase activity of the differentiated cells is related to an increase (congruent to 3-fold) in the number of hormonal receptors and not to a significant change in receptor binding affinity (Kd 4.6 X 10(8) M-1). These alterations in calcitonin and somatostatin responsiveness suggest a possible regulatory role for these hormones during embryonic development. Furthermore, the results indicate that changes in adenylate cyclase hormonal responsiveness might serve as useful markers during early stages of human embryonal carcinoma cell differentiation. |
