Immunochemical analysis of the alpha-subunit of the stimulatory G-protein of adenylyl cyclase in patients with Albright's hereditary osteodystrophy.

Albright's hereditary osteodystrophy (AHO) is an autosomal dominant disorder characterized by an unusual phenotypic appearance and reduced biological activity of the alpha-subunit of the stimulatory G-protein of adenylyl cyclase (Gs alpha). In most AHO patients deficient Gs alpha activity is associated with generalized target organ resistance to hormones that act via stimulation of adenylyl cyclase. This form of the disorder is termed pseudohypoparathyroidism type Ia (PHP Ia). By contrast, other patients with Gs alpha deficiency fail to demonstrate clinical evidence of hormone resistance and are considered to have the related disorder pseudopseudohypoparathyroidism (pseudoPHP). Previous studies demonstrating deficient Gs alpha bioactivity in cell membranes from patients with AHO used functional assays that were unable to distinguish between reduced amounts of normal Gs alpha protein and normal amounts of defective Gs alpha protein. In the present study we used specific Gs alpha antisera to analyze immunoactive Gs alpha protein in erythrocyte and fibroblast membranes from 20 patients with AHO who had either normal or reduced levels of Gs alpha mRNA. Cell membranes were subjected to immunoblot analysis using Gs alpha antisera developed against synthetic peptides corresponding to amino acid sequences in the amino- or carboxyl-terminus of the Gs alpha molecule. Fibroblast membranes from patients with AHO who had reduced or normal levels of Gs alpha mRNA contained both the 45- and 52-kDa forms of the Gs alpha protein in quantities that were significantly less [mean +/- SE, 52 +/- 6%; (n = 8) for reduced mRNA and 35 +/- 19% (n = 2) for normal mRNA, percentage of control values] than those present in membranes from normal subjects. Similar reductions were found in the level of the 45-kDa form of Gs alpha in erythrocyte membranes from all AHO patients studied [40 +/- 4% (mean +/- SE) of control values]. No abnormal forms of Gs alpha protein were detected. Cell membranes from patients with PHP type Ia and from patients with pseudoPHP contained levels of immunoactive Gs alpha that were equivalently reduced (43 +/- 4% vs. 42 +/- 5%, respectively). By contrast, erythrocyte membranes from patients with PHP type Ib, who have normal Gs alpha activity, had normal levels of Gs alpha immunoactivity (101 +/- 7%). These results indicate that most patients with AHO have reduced levels of Gs alpha protein as the basis for deficient Gs alpha bioactivity.