Rapid GDP release from G sub(s alpha ) in patients with gain and loss of endocrine function

• Published in: Nature (London) Vol. 371; no. 6493; pp. 164 - 168
• Main Authors: Iiri, T, Herzmark, P, Nakamoto, J M, Van Dop, C, Bourne, H R
• Format: Journal Article
• Language: English
• Published: 01-01-1994
• Subjects: alpha chain; GDP; genes; guanine nucleotide-binding protein; hyperactivity; hypoactivity; luteinizing hormone; man; parathyroid hormone; receptors; release; temperature sensitive mutant; thyroid-stimulating hormone
• ISSN: 0028-0836

Luteinizing hormone stimulates testicular Leydig cells to produce testosterone by binding to a receptor that activates the G protein G sub(s) and adenylyl cyclase. Testotoxicosis is a form of precocious puberty in which the Leydig cells secrete testosterone in the absence of luteinizing hormone, often due to constitutive activation of the luteinizing hormone receptor and (indirectly) G sub(s). Here we study two unrelated boys suffering from a paradoxical combination of testotoxicosis and pseudohypoparathyroidism type Ia (PHP-Ia), a condition marked by resistance to hormones acting through cyclic AMP (parathyroid hormone and thyroid-stimulating hormone) as well as a 50% decrease in erythrocyte G sub(s) activity (the remaining 50% is due to the normal G sub(s) allele). In both patients, a mutation in the gene encoding the G sub(s) alpha -subunit replaced alanine at position 366 with serine. We show that this alpha sub(s)-A366S mutation constitutively activates adenylyl cyclase in vitro, causing hormone-independent cAMP accumulation when expressed in cultured cells, and accounting for the testotoxicosis phenotype (as cAMP stimulates testosterone secretion). Although alpha sub(s)-A366S is quite stable at testis temperature, it is rapidly degraded at 37 degree C, explaining the PHP-Ia phenotype caused by loss of G sub(s) activity. In vitro experiments indicate that accelerated release of GDP causes both the constitutive activity and the thermolability of alpha sub(s)-A366S.