Dexamethasone‐dependent expression of β1–24 corticotropin stimulated adenylate cyclase during adipose conversion of 3T3‐F442A cells

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Abstract
When 3T3-F442A preadipocytes were grown in culture media supplemented with corticosteroid poor fetal calf serum and insulin they differentiated into adipocytes. Glycerophosphate dehydrogenase, a marker of terminal differentiation, developed a 600-fold increase of activity whereas the adenylate cyclase system remained unresponsive to the synthetic ACTH(1–24) analog. In contrast, 3T3-F442A adipocytes, differentiated in the presence of dexamethasone, exhibited an adenylate cyclase activity which was stimulated 4-fold by ACTH(1–24). The stimulation of the adenylate cyclase activity by GTPγS remained unchanged (about 20–25-fold) suggesting that the G regulatory coupling protein was not functionally modified by dexamethasone. Binding studies with 125I-ACTH revealed that specific cellular binding could be evidenced in dexamethasone-treated cells while control adipocytes did not exhibit any specific binding of 125 I-ACTH. These findings lend support to the hypothesis that the setting off of this ACTH responsiveness in 3T3-F442A cells is regulated by dexamethasone after cells are committed to adipose differentiation