"Defective" receptors in steroid-resistant conditions may be proteolytic artifacts

Area of Science:

• Molecular Endocrinology
• Biochemistry
• Cell Biology

Background:

• Steroid receptor structure and function are critical for cellular response to hormones.
• Resistance to steroid treatment can occur despite normal receptor quantity, suggesting structural abnormalities.
• Understanding receptor variations is key in healthy, malignant, and tumor tissues.

Purpose of the Study:

• To investigate if structural defects in steroid receptors cause resistance to steroid treatment.
• To explore intrinsic variations in steroid receptor structures across different tissues and conditions.
• To characterize the physicochemical properties of estrogen, progestin, and glucocorticoid receptors.

Main Methods:

• Stabilization and physicochemical characterization of steroid receptors using chromatography and ultracentrifugation.
• Analysis of estrogen and progestin receptors from human breast and gynecologic specimens.
• Analysis of glucocorticoid receptors from rodent and human tissues, including lymphocytes and leukemic cells.
• Assay of endopeptidase activities using fluorometric methods with AMC-derivatives.

Main Results:

• Stabilized receptors (estrogen, progestin, glucocorticoid) form large, oligomeric complexes with consistent physicochemical properties.
• Unstabilized receptors are susceptible to degradation by endogenous proteinases, particularly in tissues like rat kidney and human endometrium.
• Receptor size variations correlate with specific endopeptidase activities, suggesting proteolysis as a cause of structural alteration.
• A 'lysine-specific' endopeptidase from rat kidney cytosol was shown to degrade glucocorticoid receptors.

Conclusions:

• Steroid receptor resistance may stem from structural defects, potentially caused by proteolytic degradation.
• Tissue-specific proteinases can significantly alter steroid receptor structure, impacting their function.
• Understanding these structural variations and degradation pathways is crucial for predicting and overcoming steroid resistance.