Endocrine Abstracts

The adrenocorticotrophin hormone (ACTH) receptor, also known as the melanocortin-2-receptor (MC2R), is a key mediator of cortisol synthesis in the adrenal gland. Over 40 loss-of-function MC2R mutations have been described to give rise to familial glucocorticoid deficiency type-1 (FGD1). In contrast, to date only one naturally occurring gain-of-function mutation, F278C, has been identified in a patient with ACTH-independent Cushing’s syndrome. Previous work has demonstrated that F278C results in enhanced cAMP generation and impaired desensitisation and internalisation compared to wild-type MC2R receptor. Herein using kinetic biosensors in a naïve cell culture system, we build upon previous findings that the F278C mutation results in increased cAMP signalling. Additionally, we show direct interaction of MC2R with beta-1-arrestin (ARRB1), a protein involved in the sequestration of phosphorylated GPCRs away from the cell surface and that the F278C mutation has impaired recruitment of ARRB1. We have further interrogated this mutation by modifying the downstream putative phosphorylation-site S280 and show very similar trends to that of the F278C mutation, this aligns with the hypothesis that F278 is involved in the phosphorylation of residue S280. In summary, our current data adds to the mechanistic reasons of how naturally occurring human MC2R mutation (F278C) leads to ACTH-independent Cushing’s Disease.