Endocrinology, Vol 137, 3291-3294, Copyright © 1996 by Endocrine Society

ARTICLES

Agonist and receptor binding properties of adrenocorticotropin peptides using the cloned mouse adrenocorticotropin receptor expressed in a stably transfected HeLa cell line

S Kapas, FM Cammas, JP Hinson and AJ Clark
Department of Chemical Endocrinology, St. Bartholomew's Hospital Medical College, West Smithfield, London, United Kingdom.

The cloned mouse ACTH receptor was expressed in stably transfected human HeLa cells that lack an endogenous melanocortin receptor. ACTH[1- 39] and several N- and C-terminally truncated analogues of ACTH were studied for their ability to stimulate cAMP generation and to displace bound 125I-ACTH. Only three of the peptides tested, ACTH[1-24], ACTH[1- 39], and ACTH[1-17] were found to have agonist activity with EC50 values of 7.5, 57, and 49 x 10(-12) M respectively. Two peptides, ACTH[11-24] and ACTH[7-39], were devoid of agonist activity but had substantial competitive antagonist activity with IC50 values of approximately 10(-9) M. In binding studies, ACTH[1-39] and ACTH[1-24] were able to fully displace bound ligand, and Scatchard analysis indicated a dissociation constant (KD) of 0.84 and 0.94 x 10(-9) M for the two peptides, respectively. ACTH[1-17], ACTH[11-24], and ACTH[7-39] were only capable of displacing 60-70% of bound ligand. A three-site model for the interaction of ACTH and its receptor is proposed on the basis of these findings.

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