Ca2+/S100 Proteins Act as Upstream Regulators of the Chaperone-associated Ubiquitin Ligase CHIP (C Terminus of Hsc70-interacting Protein) |
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Authors: | Seiko Shimamoto Yasuo Kubota Fuminori Yamaguchi Hiroshi Tokumitsu Ryoji Kobayashi |
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Institution: | From the Departments of ‡Signal Transduction Sciences.;¶Dermatology, and ;‖Cell Physiology, Kagawa University Faculty of Medicine, 1750-1 Ikenobe, Miki-cho, Kita-gun, Kagawa 761-0793 and ;the §Nano-micro Structure Device Integrated Research Center, Kagawa University, 2217-20 Hayashi-cho, Takamatsu 761-0396, Japan |
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Abstract: | The U-box E3 ubiquitin ligase CHIP (C terminus of Hsc70-interacting protein) binds Hsp90 and/or Hsp70 via its tetratricopeptide repeat (TPR), facilitating ubiquitination of the chaperone-bound client proteins. Mechanisms that regulate the activity of CHIP are, at present, poorly understood. We previously reported that Ca2+/S100 proteins directly associate with the TPR proteins, such as Hsp70/Hsp90-organizing protein (Hop), kinesin light chain, Tom70, FKBP52, CyP40, and protein phosphatase 5 (PP5), leading to the dissociation of the interactions of the TPR proteins with their target proteins. Therefore, we have hypothesized that Ca2+/S100 proteins can interact with CHIP and regulate its function. GST pulldown assays indicated that Ca2+/S100A2 and S100P bind to the TPR domain and lead to interference with the interactions of CHIP with Hsp70, Hsp90, HSF1, and Smad1. In vitro ubiquitination assays indicated that Ca2+/S100A2 and S100P are efficient and specific inhibitors of CHIP-mediated ubiquitination of Hsp70, Hsp90, HSF1, and Smad1. Overexpression of S100A2 and S100P suppressed CHIP-chaperone complex-dependent mutant p53 ubiquitination and degradation in Hep3B cells. The association of the S100 proteins with CHIP provides a Ca2+-dependent regulatory mechanism for the ubiquitination and degradation of intracellular proteins by the CHIP-proteasome pathway. |
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Keywords: | Calcium-binding Proteins Protein Degradation S100 Proteins Ubiquitin Ligase Ubiquitination CHIP TPR Domain |
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