ARMC5-CUL3 E3 ligase targets full-length SREBF in adrenocortical tumors

Area of Science:

• Endocrinology
• Molecular Biology
• Oncology

Background:

• Bilateral macronodular adrenal hyperplasia (BMAH) is linked to inactivating ARMC5 mutations.
• ARMC5 is a tumor suppressor, but its function in adrenal regulation is unclear.
• Understanding ARMC5's molecular role is crucial for BMAH pathogenesis.

Purpose of the Study:

• To elucidate the molecular function of ARMC5 in adrenal cells.
• To identify ARMC5's interaction partners and regulatory mechanisms.
• To investigate the role of the ARMC5-SREBP pathway in BMAH.

Main Methods:

• Biochemical purification using SREBP as bait to identify ARMC5 interactors.
• Co-immunoprecipitation and ubiquitination assays to study protein interactions.
• Cellular studies in H295R cells involving gene silencing and mutation analysis.

Main Results:

• ARMC5 interacts with SREBP via its Armadillo repeat and with CUL3 via its BTB domain.
• ARMC5 induces proteasome-dependent degradation of full-length SREBP through ubiquitination.
• ARMC5 mutations found in BMAH abolish its SREBP degradation activity.
• ARMC5 silencing increases SREBP levels and upregulates SREBP2 target genes in adrenocortical cells.

Conclusions:

• ARMC5 functions as a substrate adaptor protein linking SREBP to the CUL3-based E3 ligase complex.
• The SREBP pathway is implicated in the pathogenesis of bilateral macronodular adrenal hyperplasia.
• ARMC5's tumor-suppressive activity is mediated through SREBP degradation.