The cochaperone and ubiquitin ligase CHIP in protein quality control

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  • March 22, 2019
Creator
  • Dai, Qian
    • Affiliation: School of Medicine, Department of Pharmacology
Abstract
  • Protein quality control is essential for living cells to maintain homeostasis during normal growth conditions as well as upon stress challenges. Molecular chaperones and the ubiquitin-proteasome system are the two arms of the cellular protein quality control system. CHIP is an Hsp70/Hsp90 cochaperone that inhibits ATPase activity of chaperones and enhances protein folding in vivo. CHIP is also a chaperone-dependent E3 ubiquitin ligase that diverts chaperone substrates to the proteasome. Therefore, CHIP regulates both arms of the protein quality control system. My studies have established that CHIP regulates the stress-chaperone response through induced trimerization and transcriptional activation of HSF1, which leads to transcriptional upregulation of heat shock proteins. This upregulation is required for cells to cope with stress as CHIP (-/-) murine fibroblasts have decreased viability and increased apoptosis after heat shock or protein damaging agent treatment. Activation of HSF1 by CHIP is essential for the cells to cope with stress challenges. E3 ubiquitin ligase activity of CHIP has been implicated in the degradation of a variety of chaperone-bound cytoplasmic proteins. Using a proteomics approach, we have identified BAG2 as a common component of CHIP holocomplexes in vivo. Binding assays indicate that BAG2 associates with CHIP as part of a ternary complex with Hsc70. BAG2 is an efficient and specific inhibitor of CHIP-dependent ubiquitin ligase activity. This activity is due, in part, to inhibition of interactions between CHIP and its cognate ubiquitin-conjugating enzyme, UbcH5a. The association of BAG2 with CHIP provides a cochaperone-dependent regulatory mechanism for preventing unregulated ubiquitylation of misfolded proteins by CHIP. Taken together, my work has established the mechanism of CHIP to regulate the stress response and identified a regulatory factor for its E3 ubiquitin ligase activity.
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  • In Copyright
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  • Patterson, Cam
Degree granting institution
  • University of North Carolina at Chapel Hill
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