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Title: Molecular mechanism of glucocorticoid action
Author: Attarzadeh Yazdi, Ghassem
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2006
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The aim of this thesis project was to investigate the mechanisms by which glucocorticoid hormones regulate the activity of BK channels in human embryonic kidney 293 (HEK293) cells as the model system for glucocorticoids-action. It was shown that glucocorticoids act via endogenously expressed type II receptors in a concentration- and time-dependent manner in these cells. Dexamethasone (100 nM) had no significant effect on Dexras1 mRNA but significantly increased serum- and glucocorticoid-induced protein kinase 1 (SGK-1) mRNA. Biochemical analysis showed that SGK-1 protein is increased by dexamethasone in a Triton X-100 insoluble fraction. Further work was directed toward analysing the possible association of SGK-1 and protein phosphatases with two BK channel α-subunit variants: ZERO-BK and STREX-BK, the latter contains the 59 amino-acid splice insert encoded by the stress hormone induced exon (STREX). HEK293 cells stably expressing the respective channel subunits were analysed. Immunoprecipitations with antisera directed against the BK α-subunits showed that protein phosphatase 2A (PP2A) but not SGK-1 is constitutively associated with the STREX as well as the ZERO variant BK channel. Furthermore, the cytoplasmic C-terminal segment of the STREX-BK channel was necessary for cell-surface expression of the channel and the association of the channel with PP2A. Dexamethasone, failed to change the apparent amount of immunoreactive PP2A co-immunoprecipitating with the channel. In conclusion: SGK-1 but not Dexras1 is a protein rapidly induced by dexamethasone in HEK293 cells. PP2A but not SGK-1 is in complex with both ZERO and STREX-BK channels, and dexamethasone does not alter this association. The cytoplasmic tail of the BK channels is essential for PP2A interaction.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available