Parathyroid hormone signaling via G alpha s is selectively inhibited by an NH sub(2)-terminally truncated G alpha s: Implications for pseudohypoparathyroidism

• Published in: Journal of bone and mineral research 2011-10, Vol.26 (10), p.2473-2485
• Main Authors: Puzhko, Svetlana, Goodyer, Cynthia Gates, Kerachian, Mohammad Amin, Canaff, Lucie, Misra, Madhusmita, Jueppner, Harald, Bastepe, Murat, Hendy, Geoffrey N
• Format: Article
• Language: English
• ISSN: 0884-0431; 1523-4681
• DOI: 10.1002/jbmr.461

Pseudohypoparathyroid patients have resistance predominantly to parathyroid hormone (PTH), and here we have examined the ability of an alternative G alpha s-related protein to inhibit G alpha s activity in a hormone-selective manner. We tested whether the GNAS exon A/B-derived NH sub(2)-terminally truncated (Tr) alpha s protein alters stimulation of adenylate cyclase by the PTH receptor (PTHR1), the thyroid-stimulating hormone (TSH) receptor (TSHR), the beta sub(2)-adrenergic receptor ( beta sub(2)AR), or the AVP receptor (V2R). HEK293cells cotransfected with receptor and full-length (FL) G alpha s plus or minus Tr alpha s protein expression vectors were stimulated with agonists (PTH [10 super(-7) to 10 super(-9)M], TSH [1 to 100mU], isoproterenol [10 super(-6) to 10 super(-8)M], or AVP [10 super(-6) to 10 super(-8)M]). Following PTH stimulation, HEK293cells cotransfected with PTHR1+FL G alpha s+Tr alpha s had a significantly lower cAMP response than those transfected with only PTHR1+FL G alpha s. Tr alpha s also exerted an inhibitory effect on the cAMP levels stimulated by TSH via the TSHR but had little or no effect on isoproterenol or AVP acting via beta sub(2)AR or V2R, respectively. These differences mimic the spectrum of hormone resistance in pseudohypoparathyroidism type 1a (PHP-1a) and type 1b (PHP-1b) patients. In opossum kidney (OK) cells, endogenously expressing the PTHR1 and beta sub(2)AR, the exogenous expression of Tr alpha s at a level similar to endogenous FL G alpha s resulted in blunting of the cAMP response to PTH, whereas that to isoproterenol was unaltered. A pseudopseudohypoparathyroid patient with Albright hereditary osteodystrophy harbored a de novo paternally inherited M1I G alpha s mutation. Similar maternally inherited mutations at the initiation codon have been identified previously in PHP-1a patients. The M1I alpha s mutant (lacking the first 59 amino acids of G alpha s) blunted the increase in cAMP levels stimulated via the PTHR1 in both HEK293 and OK cells similar to the Tr alpha s protein. Thus NH sub(2)-terminally truncated forms of G alpha s may contribute to the pathogenesis of pseudohypoparathyroidism by inhibiting the activity of G alpha s itself in a GPCR selective manner. copyright 2011 American Society for Bone and Mineral Research