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Malachite Green Assay for the Discovery of Heat-Shock Protein 90 Inhibitors
Published on: January 20, 2023
Geldanamycin-induced PCNA degradation in isolated Hsp90 complex from cancer cells
Xing Wang1, Deborah M Heuvelman, James A Carroll
1Pfizer Global Research and Development, 700 Chesterfield Parkway West, St. Louis, MO 63017, USA. xing.wang@pfizer.com
Abstract:
Hsp90 is a molecular chaperone involved in the folding and proteolytic turnover of many regulatory proteins associated with it. Some of the Hsp90 client proteins are known to be involved in tumorigenesis. An Hsp90-specific inhibitor, geldanamycin, is shown to bind to the ATP binding site of the chaperone to induce degradation of many client proteins, and results in antitumor activities. However, the mechanism of geldanamycin-induced client protein degradation is not fully understood. A large-scale immunoaffinity purification with anti-Hsp90 antibodies identified many Hsp90 client proteins from colon cancer cell line, HCT-116. One of the identified proteins, PCNA, was confirmed to be associated with Hsp90 in two additional cancer cell lines. After geldanamycin treatment, both PCNA and Hsp90 were shown to be degraded. More interestingly, this study demonstrated that in two different cancer cell lines, the degradation occurred in the isolated Hsp90 complex in vitro. This result indicated that the components responsible for the PCNA degradation are also associated with Hsp90. This finding provided a new mechanism for the Hsp90-mediated protein degradation induced by Hsp90-specific inhibitors.
Insights
Heat shock protein 90 (Hsp90) inhibitors like geldanamycin degrade client proteins, including PCNA, via an Hsp90-associated mechanism. This study reveals a novel pathway for Hsp90-mediated protein degradation in cancer cells.
Area of Science:
- Molecular biology
- Cancer research
- Protein biochemistry
Background:
- Heat shock protein 90 (Hsp90) is a molecular chaperone crucial for protein folding and turnover.
- Hsp90 client proteins are implicated in tumorigenesis.
- Hsp90 inhibitors, such as geldanamycin, exhibit antitumor activity by inducing client protein degradation.
Purpose of the Study:
- To elucidate the mechanism of geldanamycin-induced client protein degradation.
- To identify Hsp90 client proteins involved in cancer.
- To investigate the role of Hsp90 in PCNA degradation.
Main Methods:
- Immunoaffinity purification using anti-Hsp90 antibodies to identify client proteins.
- Western blotting to confirm protein association and degradation.
- In vitro degradation assays using isolated Hsp90 complexes.
Main Results:
- PCNA (Proliferating Cell Nuclear Antigen) was identified as an Hsp90 client protein in colon cancer cells (HCT-116) and confirmed in two other cancer cell lines.
- Geldanamycin treatment led to the degradation of both PCNA and Hsp90.
- PCNA degradation was observed to occur within isolated Hsp90 complexes in vitro, indicating Hsp90-associated degradation machinery.
Conclusions:
- Hsp90 plays a direct role in the degradation of its client protein PCNA.
- Hsp90-specific inhibitors induce client protein degradation through an Hsp90-associated mechanism.
- This study uncovers a novel pathway for Hsp90-mediated protein degradation relevant to cancer therapy.
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