Regulation of cell survival by CIB1, a new modulator of 3-phosphoinositide-dependent protein kinase 1 (PDK1)

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  • March 21, 2019
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  • Zhao, Bin
    • Affiliation: School of Medicine, Department of Pharmacology
Abstract
  • CIB1, a calcium and integrin binding protein, was first identified by its specific binding to the cytoplasmic tail of the platelet-specific integrin [alpha]IIb. Later experiments showed that CIB1 is widely expressed and binds to a variety of proteins including many serine/threonine kinases such as PAK1, suggesting that it acts as a regulator of kinase function. The overall goal of this work has been to further identify new CIB1-binding proteins, and therefore to better understand the role of CIB1 in human diseases. Using a high stringency in silico analysis of the CIB1 protein sequence, we determined that CIB1 contains a consensus PDK1 hydrophobic binding motif. Further detailed experiments confirmed that CIB1 binds PDK1 both in vitro and in cells. PDK1, 3-phosphoinositide-dependent protein kinase 1, is a member of the AGC protein kinase family and plays an important role in regulating cell growth, survival, and cell cycle progression by activating other AGC kinases such as Akt, S6K, or RSK. However, how PDK1 itself is regulated is less clear. We demonstrated that the binding of CIB1 to PDK1 upregulates PDK1 kinase activity and promotes cell survival. We found that CIB1 depletion significantly enhances cell apoptosis in response to a variety of apoptotic stimuli, a response significantly rescued by PDK1 overexpression, whereas CIB1 overexpression protects cells from apoptotic stimuli in a PDK1-dependent manner. The ability of CIB1 to promote cell survival appears to require both membrane localization and PDK1 binding, since CIB1 mutants that either do not bind PDK1 or do not localize to membranes induce a marked redistribution of PDK1, and no longer protect cells from apoptosis. Moreover, depletion of CIB1 reduces Akt and RSK3 phosphorylation by PDK1, suggesting a CIB1/PDK1/Akt or RSK3 dependent pathway. Taken together, our results indicate that CIB1 is an important upstream activator of PDK1, thereby resisting apoptosis and promoting cell survival.
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  • In Copyright
Advisor
  • Parise, Leslie
Degree granting institution
  • University of North Carolina at Chapel Hill
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  • Open access
Date uploaded
  • October 19, 2010

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