Immunochemical analysis of the α-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 α-subunit of the stimulatory G-protein of adenylyl cyclase (G_sα). In most AHO patients deficient G_sα 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 G_sα deficiency fail to demonstrate clinical evidence of hormone resistance and are considered to have the related disorder pseudopseudohypoparathyroidism (pseudoPHP). Previous studies demonstrating deficient G_sα bioactivity in cell membranes from patients with AHO used functional assays that were unable to distinguish between reduced amounts of normal G_sα protein and normal amounts of defective G_sα protein. In the present study we used specific G_sα antisera to analyze immunoactive G_sα protein in erythrocyte and fibroblast membranes from 20 patients with AHO who had either normal or reduced levels of G_sα mRNA. Cell membranes were subjected to immunoblot analysis using G_sα antisera developed against synthetic peptides corresponding to amino acid sequences in the amino- or carboxyl-terminus of the G_sα molecule. Fibroblast membranes from patients with AHO who had reduced or normal levels of G_sα mRNA contained both the 45-and 52-kDa forms of the G_sα 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 G_sα in erythrocyte membranes from all AHO patients studied [40 ± 4% (mean ± SE) of control values]. No abnormal forms of G_sα protein were detected. Cell membranes from patients with PHP type Ia and from patients with pseudoPHP contained levels of immunoactive G_sα that were equivalently reduced (43 ± 4% vs. 42 ± 5%, respectively). By contrast, erythrocyte membranes from patients with PHP type Ib, who have normal G_sα activity, had normal levels of G_sα immunoactivity (101 ± 7%). These results indicate that most patients with AHO have reduced levels of G_sα protein as the basis for deficient G_sα bioactivity.