Parathyroid hormone signaling via Gαs is selectively inhibited by an NH2-terminally truncated Gαs: Implications for pseudohypoparathyroidism

Authors

  • Svetlana Puzhko,

    1. Endocrine Research Laboratory, McGill University, Montreal, Quebec, Canada
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  • Cynthia Gates Goodyer,

    Corresponding author
    1. Endocrine Research Laboratory, McGill University, Montreal, Quebec, Canada
    2. Department of Pediatrics, McGill University, Montreal, Quebec, Canada
    3. Department of Medicine, McGill University, Montreal, Quebec, Canada
    • Endocrine Research Laboratory, Room 415/1, McGill University–Montreal Children's Hospital Research Institute, 4060 Ste. Catherine Street West, Montreal, Quebec, Canada H3Z 2Z3.
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  • Mohammad Amin Kerachian,

    1. Calcium Research Laboratory, Royal Victoria Hospital, Montreal, Quebec, Canada
    2. Department of Human Genetics, McGill University, Montreal, Quebec, Canada
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  • Lucie Canaff,

    1. Calcium Research Laboratory, Royal Victoria Hospital, Montreal, Quebec, Canada
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  • Madhusmita Misra,

    1. Neuroendocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA
    2. Pediatric Endocrine Unit, MassGeneral forf Children and Harvard Medical School, Boston, MA, USA
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  • Harald Jüppner,

    1. Pediatric Nephrology Unit, MassGeneral for Children and Harvard Medical School, Boston, MA, USA
    2. Endocrine Unit, Department of Medicine, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA
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  • Murat Bastepe,

    1. Endocrine Unit, Department of Medicine, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA
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  • Geoffrey N Hendy

    Corresponding author
    1. Department of Medicine, McGill University, Montreal, Quebec, Canada
    2. Calcium Research Laboratory, Royal Victoria Hospital, Montreal, Quebec, Canada
    3. Department of Human Genetics, McGill University, Montreal, Quebec, Canada
    4. Department of Physiology, McGill University, Montreal, Quebec, Canada
    5. Hormones and Cancer Research Unit, Royal Victoria Hospital, Montreal, Quebec, Canada
    • Calcium Research Laboratory, Room H4.67, Royal Victoria Hospital, 687 Pine Avenue West, Quebec, Canada H3A 1A1.
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Abstract

Pseudohypoparathyroid patients have resistance predominantly to parathyroid hormone (PTH), and here we have examined the ability of an alternative Gαs-related protein to inhibit Gαs activity in a hormone-selective manner. We tested whether the GNAS exon A/B-derived NH2-terminally truncated (Tr) αs protein alters stimulation of adenylate cyclase by the PTH receptor (PTHR1), the thyroid-stimulating hormone (TSH) receptor (TSHR), the β2-adrenergic receptor (β2AR), or the AVP receptor (V2R). HEK293 cells cotransfected with receptor and full-length (FL) Gαs ± Tr αs protein expression vectors were stimulated with agonists (PTH [10−7 to 10−9 M], TSH [1 to 100 mU], isoproterenol [10−6 to 10−8 M], or AVP [10−6 to 10−8 M]). Following PTH stimulation, HEK293 cells cotransfected with PTHR1 + FL Gαs + Tr αs had a significantly lower cAMP response than those transfected with only PTHR1 + FL Gαs. Tr αs 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 β2AR 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 β2AR, the exogenous expression of Tr αs at a level similar to endogenous FL Gαs 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 Gαs mutation. Similar maternally inherited mutations at the initiation codon have been identified previously in PHP-1a patients. The M1I αs mutant (lacking the first 59 amino acids of Gαs) blunted the increase in cAMP levels stimulated via the PTHR1 in both HEK293 and OK cells similar to the Tr αs protein. Thus NH2-terminally truncated forms of Gαs may contribute to the pathogenesis of pseudohypoparathyroidism by inhibiting the activity of Gαs itself in a GPCR selective manner. © 2011 American Society for Bone and Mineral Research

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