Induction of adenylate cyclase in a mammary carcinoma cell line by human corticosteroid-binding globulin.

Corticosteroid-Binding globulin (CBG) is a plasma protein that binds certain steroid hormones, mainly cortisol and progesterone. It has been demonstrated recently that specific binding sites for this protein exist on cell membranes. In this communication we establish that binding to these sites results in the induction of adenylate cyclase activity and the accumulation of cAMP in MCF-7 cells. These events are critically dependent upon a steroid being bound to CBG. These data are consistent with the hypothesis that CBG is a prohormone which is activated when cortisol is bound to it.