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Vitamin D3--resistant fibroblasts have immunoassayable 1,25-dihydroxyvitamin D3 receptors
Abstract:
Cultured fibroblasts obtained from patients with tissue resistance to 1,25-dihydroxyvitamin D3 (vitamin D3--dependent rickets, type II) contain normal, low, or undetectable concentrations of this hormone's receptor protein as measured by a ligand-binding assay. Extracts from these cells were evaluated for receptors by immunoassay with a recently developed monoclonal antibody to the chick receptor. The results show that a protein sedimenting at 3.7S and recognizable by the antibody exists in comparable concentrations in cells from both normal and resistant patients, irrespective of the hormone-binding abnormalities of the cells. This implies that deficiencies in hormone binding associated with inherited tissue resistance to 1,25-dihydroxyvitamin D3 probably arise from structural variations in the receptor molecule and not from defective receptor synthesis.
Insights
Patients with vitamin D3-dependent rickets type II have receptor defects. Though hormone binding is abnormal, the vitamin D receptor protein is present, suggesting structural variations, not synthesis issues.
Area of Science:
- Endocrinology
- Molecular Biology
- Genetics
Background:
- Tissue resistance to 1,25-dihydroxyvitamin D3 causes vitamin D3-dependent rickets type II.
- Patients exhibit varying levels of the vitamin D receptor (VDR) protein, from normal to undetectable, via ligand-binding assays.
Purpose of the Study:
- To investigate the presence and nature of the vitamin D receptor (VDR) in fibroblasts from patients with vitamin D resistance.
- To differentiate between defective VDR synthesis and structural abnormalities in VDRs.
Main Methods:
- Fibroblast cultures from normal individuals and patients with vitamin D resistance were used.
- Immunoassay with a monoclonal antibody against the chick VDR was employed to detect the receptor protein.
- Sedimentation analysis (3.7S) was performed to characterize the receptor.
Main Results:
- A protein recognized by the monoclonal antibody, sedimenting at 3.7S, was found in comparable concentrations in both normal and resistant cells.
- The presence of this protein was independent of the hormone-binding abnormalities observed in the resistant cells.
Conclusions:
- The findings suggest that inherited tissue resistance to 1,25-dihydroxyvitamin D3 is likely due to structural defects in the vitamin D receptor molecule.
- Defective receptor synthesis is unlikely to be the primary cause of this condition.
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