The role of extracellular calcium in corticotropin-stimulated steroidogenesis.
The role of extracellular Ca2+ in the binding of corticotropin (ACTH) to adrenocortical cell receptors as well as in the post-binding events involved in steroidogenesis were investigated. Binding studies using [125I-Tyr23,Phe2,Nle4]ACTH (1-38) peptide showed that extracellular Ca2+ is essential not only for the interaction of ACTH with its receptor, but also for continued occupancy of the receptor. In view of the requirement of Ca2+ for binding the hormone to the receptor, the role of Ca2+ in post-receptor events was investigated by covalently attaching the hormone to its receptor by photoaffinity labeling in the presence of Ca2+. Persistent activation of steroidogenesis induced by photoaffinity labeling in the presence of Ca2+ was depressed when cells were incubated in medium containing EGTA but was unaffected when the cells were merely washed and incubated in Ca2+-free medium. In the presence of EGTA, 8-Br-cAMP partially restored persistent activation of steroidogenesis. The concentration of extracellular Ca2+ required for restoring steroidogenesis was 10-fold lower than the concentration of Ca2+ needed for optimal binding of ACTH to its receptor. These results suggest that the primary role of extracellular Ca2+ in the action of ACTH is to facilitate the association of the hormone with its receptor.
Cheitlin
R
R
Buckley
D I
DI
Ramachandran
J
J
D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000302:Adrenal Cortex / Q000378:metabolism*; D000324:Adrenocorticotropic Hormone / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology*; D000345:Affinity Labels / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D000242:Cyclic AMP / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology; D008297:Male; D010782:Photolysis; D051381:Rats; D011919:Rats, Inbred Strains; D011956:Receptors, Cell Surface / Q000378:metabolism; D018043:Receptors, Corticotropin; D013256:Steroids / Q000096:biosynthesis*
D000345:Affinity Labels; D011956:Receptors, Cell Surface; D018043:Receptors, Corticotropin; D013256:Steroids; D015124:8-Bromo Cyclic Adenosine Monophosphate; D004533:Egtazic Acid; C026458:ACTH, 2-nitro-4-azidophenylsulfenyl-; D000324:Adrenocorticotropic Hormone; D000242:Cyclic AMP; D002118:Calcium