Functional characterization of GNAS mutations found in patients with pseudohypoparathyroidism type Ic defines a new subgroup of pseudohypoparathyroidism affecting selectively Gsα-receptor interaction

Susanne Thiele (1) , Luisa de Sanctis (2) , Ralf Werner (1) , Joachim Grötzinger (3) , Cumhur Aydin (4) , Harald Jüppner (5) , Murat Bastepe (5) , Olaf Hiort (1)

1 Department of Pediatrics
2 Department of Pediatrics
3 Institute of Biochemistry [Kiel, Allemagne]
4 Center Dental Sciences
5 Departments of Medicine and Pediatrics

Objective: Pseudohypoparathyroidism type Ia (PHPIa) is caused by GNAS mutations leading to deficiency of the α-subunit of stimulatory G proteins (Gsα) that mediate signal transduction of G protein-coupled receptors via cAMP. PHP type Ic (PHPIc) and PHPIa share clinical features of Albright hereditary osteodystrophy (AHO); however, in-vitro activity of solubilized Gsα protein is normal in PHPIc but reduced in PHPIa. Methods: We screened 32 patients classified as PHPIc for GNAS mutations and identified three mutations (p.E392K, p.E392X, p.L388R) in four unrelated families. These and one novel mutation associated with PHPIa (p.L388P) were introduced into a pcDNA3.1(-) expression vector encoding Gsα wild-type and expressed in a Gsα-null cell line (Gnas E2-/E2-). To investigate receptor-mediated cAMP accumulation, we stimulated the endogenous expressed β2-adrenergic receptor, or the co-expressed PTH- or TSH receptors, and measured the synthesized cAMP by RIA. The results were compared to receptor-independent cholera toxin-induced cAMP accumulation. Results: In PHPIc mutations, significantly reduced or completely disrupted receptor-mediated activation was found, but they displayed normal receptor-independent activation. In contrast, PHPIa associated Gsα-388P disrupted both receptor-mediated activation and receptor-independent activation. Conclusions: We present a new subgroup of PHP that is caused by Gsα deficiency and selectively affects receptor-coupling functions of Gsα

Mots clés: Life Sciences

Susanne Thiele, Luisa de Sanctis, Ralf Werner, Joachim Grötzinger, Cumhur Aydin, et al.. Functional characterization of GNAS mutations found in patients with pseudohypoparathyroidism type Ic defines a new subgroup of pseudohypoparathyroidism affecting selectively Gsα-receptor interaction. Human Mutation, 2011, ⟨10.1002/humu.21489⟩. ⟨hal-00631260⟩