Advisory Committee Chair
Richard Jope
Advisory Committee Members
Gail Johnson
Mathieu Lesort
Scott Wilson
Michael Wyss
Document Type
Dissertation
Date of Award
2007
Degree Name by School
Doctor of Philosophy (PhD) Heersink School of Medicine
Abstract
Proper regulation of survival signaling is critical for all organisms. One important signaling cascade involved in the coordinated effort to control signals influencing cell fate is the phosphatidylinositol 3-kinase (PI3K)-Akt-glycogen synthase kinase 3β (GSK3β) signaling cascade. Following activation by growth factors the PI3K-Akt pathway promotes cell survival and, cell death is facilitated following inhibition of Akt. Many factors influence the function of the Akt-GSK3β signaling dyad, including phosphorylation, protein complex formation and subcellular localization. Previous work had demonstrated that the 90kDa heat shock protein, HSP90, directly binds and stabilizes Akt. Furthermore, several heat shock proteins including HSP90 and HSP105 can modulate cell survival following various insults. Therefore, the goals of this research were to test if heat shock proteins, either directly or indirectly, could regulate signaling to GSK3β, modulate GSK3β-mediated apoptosis, or direct nuclear localization of GSK3β. The HSP90 inhibitor geldanamycin was used to block HSP90 function followed by examination of insulin like growth factor-1 (IGF-1) or insulin-induced signaling. HSP90 inhibition enhanced growth factor-induced phosphorylation and activation of Akt and subsequent phosphorylation and inactivation of GSK3β, indicating that HSP90 normally acts to buffer the magnitude of growth factor signaling. Hsp90 dampened Akt signaling by facilitating phosphatase-mediated dephosphorylation of Akt. ii Endoplasmic reticulum (ER) stress, in opposition to growth factors, promotes apoptotic signaling. GSK3 and HSP105 were found to interact and both modulate ER stress-induced apoptotic signaling. Knockdown of HSP105 attenuated ER stress-induced caspase-3 activation down stream of the proapoptotic molecule C/EBP homologous protein (CHOP), indicating that HSP105 facilitates ER stress-induced caspase-3 activation. GSK3 also facilitates ER stress-induced apoptotic signaling, however GSK3 is acting upstream of CHOP expression. Thus HSP105 and GSK3 interact and regulate distinct points in the ER stress-induced apoptotic signaling pathway. Many of the actions of GSK3β are influenced by tightly controlled nuclear localization. Nuclear localization of GSK3β is controlled by a cohort of factors including a bipartite nuclear localization sequence (NLS), intramolecular interactions and stimulus-induced release from protein complexes. Overall, this work reveals novel roles for heat shock proteins in the regulation of survival signaling. Moreover, the molecular mechanism regulating the nuclear localization of GSK3β were discovered.
Recommended Citation
Meares, Gordon P., "Directing AKT And GSK3ß: Molecular Insights Into Cell Signaling And Survival" (2007). All ETDs from UAB. 3761.
https://digitalcommons.library.uab.edu/etd-collection/3761