HECTD3 Mediates an HSP90-Dependent Degradation Pathway for Protein Kinase Clients

Area of Science:

• Molecular Biology
• Oncology
• Biochemistry

Background:

• Heat shock protein 90 (HSP90) chaperones client proteins, including oncogenic kinases, and its inhibition is a cancer therapeutic strategy.
• HSP90 inhibition promotes client protein ubiquitylation and proteasomal degradation, but the underlying mechanism and involved E3 ligases remain unclear.

Purpose of the Study:

• To elucidate the mechanism by which HSP90 inhibition triggers ubiquitylation and proteasomal degradation of client proteins.
• To identify the E3 ubiquitin ligases responsible for the degradation of the HSP90 client kinase CRAF.

Main Methods:

• Utilized a siRNA screen to identify components of CRAF degradation pathways.
• Investigated the association of HECTD3 with HSP90 and CRAF using cellular assays.
• Analyzed the role of HECTD3's N-terminal DOC domain in protein degradation.

Main Results:

• Identified two independent degradation pathways for CRAF: one involving CUL5/Elongin B/C, and another involving the E3 ligase HECTD3.
• Demonstrated that HECTD3 associates with HSP90 and CRAF via its DOC domain.
• Found that HECTD3 mutations disrupting the DOC domain are present in tumors with activated MAP kinase signaling.

Conclusions:

• HECTD3 acts as a tumor suppressor by modulating the oncogenic signaling pathway involving HSP90 and CRAF.
• HECTD3-mediated degradation is a critical mechanism for controlling the levels of oncogenic client proteins.
• The findings provide new insights into HSP90 client protein regulation and potential therapeutic strategies targeting cancer signaling pathways.