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RAP46 is a negative regulator of glucocorticoid receptor action and hormone-induced apoptosis
M Kullmann1, J Schneikert, J Moll
1Forschungszentrum Karlsruhe, Institut für Genetik, Postfach 3640, D-76021 Karlsruhe, Federal Republic of Germany.
Abstract:
RAP46 was first identified by its ability to bind the glucocorticoid receptor. It has since been reported to bind several cellular proteins, including the anti-apoptotic protein Bcl-2, but the biological significance of these interactions is unknown. Here we show that RAP46 binds the hinge region of the glucocorticoid receptor and inhibits DNA binding and transactivation by the receptor. We further show that overexpression of RAP46 in mouse thymoma S49.1 cells inhibits glucocorticoid-induced apoptosis. Conversely, glucocorticoid-induced apoptosis and transactivation were enhanced after treating S49.1 cells with the immunosuppressant rapamycin, which down-regulates cellular levels of BAG-1, the mouse homolog of RAP46. The effect of rapamycin can, however, be overcome by overexpression of RAP46. These results together identify RAP46 as a protein that controls glucocorticoid-induced apoptosis through its negative regulatory action on the transactivation property of the glucocorticoid receptor.
Insights
RAP46 protein inhibits glucocorticoid receptor
Area of Science:
- Molecular Biology
- Cell Biology
- Immunology
Background:
- RAP46 protein interacts with various cellular proteins, including the glucocorticoid receptor and Bcl-2.
- The biological roles of these RAP46 interactions remain largely uncharacterized.
- Glucocorticoid receptor is a key regulator of cellular processes, including apoptosis.
Purpose of the Study:
- To elucidate the functional significance of the interaction between RAP46 and the glucocorticoid receptor.
- To investigate the role of RAP46 in regulating glucocorticoid-induced apoptosis.
- To determine the mechanism by which RAP46 influences glucocorticoid receptor activity.
Main Methods:
- Binding assays to determine the interaction site of RAP46 on the glucocorticoid receptor.
- Reporter gene assays to assess the effect of RAP46 on glucocorticoid receptor transactivation.
- Cell culture experiments using mouse thymoma S49.1 cells to study apoptosis.
- Treatment with rapamycin to modulate cellular levels of BAG-1 (mouse homolog of RAP46).
- Overexpression studies of RAP46 to assess its impact on apoptosis and transactivation.
Main Results:
- RAP46 binds to the hinge region of the glucocorticoid receptor.
- RAP46 inhibits DNA binding and transactivation mediated by the glucocorticoid receptor.
- Overexpression of RAP46 in S49.1 cells suppresses glucocorticoid-induced apoptosis.
- Rapamycin treatment enhances glucocorticoid-induced apoptosis and transactivation by down-regulating BAG-1.
- The effects of rapamycin are reversed by the overexpression of RAP46.
Conclusions:
- RAP46 acts as a negative regulator of glucocorticoid receptor transactivation.
- RAP46 controls glucocorticoid-induced apoptosis by modulating glucocorticoid receptor activity.
- The findings identify a novel mechanism for regulating apoptosis through the glucocorticoid receptor pathway.