IMMUNOCHEMICAL ANALYSIS OF THE ALPHA-SUBUNIT OF THE STIMULATORY G-PROTEIN OF ADENYLYL CYCLASE IN PATIENTS WITH ALBRIGHTS HEREDITARY OSTEODYSTROPHY

Albright’s hereditary osteodystrophy (AHO) is an autosomal dominant disorder characterized by an unusual phenotypic appearance and reduced biological activity of the asubunit of the stimulatory G-protein of adenylyl cyclase (G8α). In most AHO patients deficient G8α 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 la (PHP Ia). By contrast, other patients with G8α deficiency fail to demonstrate clinical evidence of hormone resistance and are considered to have the related disorder pseudopseudohypoparathyroidism (pseudoPHP). Previous studies demonstrating deficient G8α bioactivity in cell membranes from patients with AHO used functional assays that were unable to distinguish between reduced amounts of normal G8α protein and normal amounts of defective G8α protein. In the present study we used specific G8α antisera to analyze immunoactive G8α protein in erythrocyte and fibroblast membranes from 20 patients with AHO who had either normal or reduced levels of G8α mRNA. Cell membranes were subjected to immunoblot analysis using G8α antisera developed against synthetic peptides corresponding to amino acid sequences in the amino- or carboxyl-terminus of the G8 α molecule. Fibroblast membranes from patients with AHO who had reduced or normal levels of G8 α mRNA contained both the 45- and 52-kDa forms of the G8 α 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 G8 α in erythrocyte membranes from all AHO patients studied [40 ± 4% (mean ± SE) of control values]. No abnormal forms of G8 α protein were detected. Cell membranes from patients with PHP type la and from patients with pseudoPHP contained levels of immunoactive G8 α that were equivalently reduced (43 ± 4% vs. 42 ± 5%, respectively). By contrast, erythrocyte membranes from patients with PHP type Ib, who have normal G8 α activity, had normal levels of G8 α immunoactivity (101 ± 7%). These results indicate that most patients with AHO have reduced levels of G8 α protein as the basis for deficient G8α bioactivity. © 1990 by The Endocrine Society.