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Glucose-regulated protein-78 expression in the rat adrenal cortex
J Gregoire1, L M Mertz, R C Pedersen
1Department of Biochemistry, School of Medicine, State University of New York, Buffalo 14214.
Journal of Molecular Endocrinology
|February 1, 1993
Summary
Steroidogenesis activator polypeptide (SAP) is not primarily produced by the breakdown of glucose-regulated protein-78 (grp78). Adrenocortical grp78 levels show some ACTH control, but not enough to explain rapid SAP changes.
Area of Science:
- Endocrinology
- Molecular Biology
- Cell Biology
Background:
- Steroidogenesis activator polypeptide (SAP) is hypothesized to originate from glucose-regulated protein-78 (grp78) proteolysis.
- A sequence similarity exists between grp78's carboxyl-terminal region and SAP.
- Adrenocorticotropic hormone (ACTH) rapidly increases intracellular SAP levels.
Purpose of the Study:
- To investigate if ACTH regulates glucose-regulated protein-78 (grp78) mRNA and protein levels.
- To determine the relationship between ACTH, grp78, and SAP production in adrenal cells.
Main Methods:
- Northern blot analysis was used to assess grp78 mRNA levels in rat adrenal RNA.
- Immunoblotting was employed to quantify grp78 protein content in adrenal homogenates.
- Primary rat adrenocortical cells were cultured with and without ACTH to observe grp78 changes.
Main Results:
- Neither hypophysectomy nor dexamethasone treatment altered steady-state grp78 mRNA levels in rats over 4 days.
- Dexamethasone suppression did not significantly change grp78 protein content in adrenal homogenates.
- In cultured cells, grp78 levels decreased by 50% without ACTH but were maintained when ACTH was present.
Conclusions:
- Adrenocortical grp78 exhibits some trophic control by ACTH.
- The rapid changes observed in SAP levels are unlikely to be driven by substantial alterations in the grp78 protein pool.