Phosphorylation-dependent cleavage regulates von Hippel Lindau proteostasis and function.

Area of Science:

• Molecular Biology
• Cell Biology
• Biochemistry

Background:

• Loss of von Hippel Lindau (VHL) protein function is central to VHL diseases, including clear cell renal cell carcinoma.
• Modulating VHL proteostasis is a potential therapeutic strategy, but regulatory mechanisms remain unclear.
• VHL exists as variants (VHL30, VHL19) and multiple species, with generation and regulation unknown.

Purpose of the Study:

• To investigate the generation of VHL protein species and their role in VHL proteostasis and function.
• To elucidate the novel regulatory mechanism of VHL proteostasis and identify potential therapeutic targets.

Main Methods:

• Genetical and pharmacological approaches were used to characterize VHL species.
• Western blotting and proteasomal degradation assays were employed.
• Casein kinase 2 (CK2) mediated phosphorylation and chymotrypsin C (CTRC) cleavage were analyzed.

Main Results:

• VHL protein is cleaved at the N-terminus by chymotrypsin C before proteasomal degradation.
• Casein kinase 2-mediated phosphorylation at the VHL N-terminus is essential for this cleavage.
• Inhibiting VHL cleavage stabilizes the protein, leading to Hypoxia-Inducible Factor (HIF) downregulation.

Conclusions:

• A novel mechanism involving N-terminal cleavage regulates VHL proteostasis and function.
• This cleavage is mediated by chymotrypsin C and dependent on casein kinase 2 phosphorylation.
• Understanding this pathway provides new drug targets for VHL-deficient diseases.