The heterotrimeric (alpha beta gamma) G proteins couple cell surface receptors for light, odorants, hormones, and neurotransmitters to intracellular signal generating enzymes and ion channels. Two classes of G proteins regulate activity of hormone-sensitive adenylyl cyclase: the alpha subunit of G/s is responsible for stimulation of catalytic activity while another group of G protein alpha chains, represented by at least three forms of G/i, mediates inhibition of the enzyme. We have identified mutations in the gene encoding the alpha chain of G/s that reduce expression or function of G/salpha in patients with Albright hereditary osteodystrophy (AHO), an autosomal dominant syndrome characterized by developmental defects. Most patients with G/salpha deficiency have reduced responsiveness to parathyroid hormone (PTH) and other, but not all, hormones whose receptors are coupled by G/s to activation of adenylyl cyclase. Other AHO patients in the same kindred to not manifest hormone resistance despite identical G/salpha gene mutations. This variability in the phenotypic expression of G/salpha deficiency within and among members of a kindred remains unexplained, and provides the basis for the studies outlined in this proposal. The goal of SPECIFIC AIM 1 is to evaluate the ability of G/salpha to couple to different receptors, using a unique mutant G/salpha chain lacking a single amino acid in the carboxyl terminus. cDNAs encoding specific receptors and mutant or wild type G/salpha will be co-expressed in mammalian cells and receptor activation of G/s will be evaluated. The goal of SPECIFIC AIM 2 is to develop transformed renal proximal tubular cell lines from G/salpha-deficient AHO patients with and without in vivo hormone resistance to compare G/salpha expression and to test hormone responsiveness of a classical PTH target tissue in vitro.
In SPECIFIC AIM 3 we will investigate tissue-specific and developmental state-specific expression of G/salpha gene alleles in normal mice in order to evaluate the hypothesis that genomic imprinting modifies G/salpha protein expression.
In SPECIFIC AIM 4, we will develop mice in which one G/salpha gene has been inactivated (""""""""knock out"""""""") to determine if a 50% deficiency of G/salpha can induce the developmental defects typical of AHO and can reproduce the tissue-specific pattern of hormone resistance present in some patients. These mice will permit us to test the hypothesis that maternal inheritance of a mutant G/salpha gene allele leads to hormone resistance. These studies will provide insight into the molecular determinants that regulate receptor-G protein interaction, and will expand our understanding of the tissue- and developmental stage-specific expression of G/salpha.
| Sanchez, Janine; Perera, Erasmo; Jan de Beur, Suzanne et al. (2011) Madelung-like deformity in pseudohypoparathyroidism type 1b. J Clin Endocrinol Metab 96:E1507-11 |
| Lietman, Steven A; Germain-Lee, Emily L; Levine, Michael A (2010) Hypercalcemia in children and adolescents. Curr Opin Pediatr 22:508-15 |
| Lietman, Steven A; Yin, Lihong; Levine, Michael A (2010) SH3BP2 mutations potentiate osteoclastogenesis via PLC?. J Orthop Res 28:1425-30 |
| Lietman, Steven A; Yin, Lihong; Levine, Michael A (2008) SH3BP2 is an activator of NFAT activity and osteoclastogenesis. Biochem Biophys Res Commun 371:644-8 |
| Lietman, Steven A; Goldfarb, James; Desai, Nina et al. (2008) Preimplantation genetic diagnosis for severe albright hereditary osteodystrophy. J Clin Endocrinol Metab 93:901-4 |
| Germain-Lee, Emily L (2006) Short stature, obesity, and growth hormone deficiency in pseudohypoparathyroidism type 1a. Pediatr Endocrinol Rev 3 Suppl 2:318-27 |
| Lietman, Steven A; Ding, Changlin; Levine, Michael A (2005) A highly sensitive polymerase chain reaction method detects activating mutations of the GNAS gene in peripheral blood cells in McCune-Albright syndrome or isolated fibrous dysplasia. J Bone Joint Surg Am 87:2489-94 |
| Germain-Lee, Emily L; Schwindinger, William; Crane, Janet L et al. (2005) A mouse model of albright hereditary osteodystrophy generated by targeted disruption of exon 1 of the Gnas gene. Endocrinology 146:4697-709 |
| Lietman, Steven A; Ding, Changlin; Cooke, David W et al. (2005) Reduction in Gsalpha induces osteogenic differentiation in human mesenchymal stem cells. Clin Orthop Relat Res :231-8 |
| Jan de Beur, Suzanne; Ding, Changlin; Germain-Lee, Emily et al. (2003) Discordance between genetic and epigenetic defects in pseudohypoparathyroidism type 1b revealed by inconsistent loss of maternal imprinting at GNAS1. Am J Hum Genet 73:314-22 |
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