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

Loss of von Hippel Lindau (VHL) protein function is a key driver of VHL diseases, including sporadic and inherited clear cell renal cell carcinoma. Modulation of the proteostasis of VHL, especially missense point-mutated VHL, is a promising approach to augmenting VHL levels and function. VHL proteostasis is regulated by multiple mechanisms including folding, chaperone binding, complex formation and phosphorylation. Nevertheless, many details underlying the regulations of VHL proteostasis are unknown. VHL is expressed as two variants, VHL30 and VHL19. Furthermore, the long-form variant of VHL was often detected as multiple bands by western blotting. However, how these multiple species of VHL are generated and whether the process regulates VHL proteostasis and function are unknown. We hypothesized that the two major species are generated by VHL protein cleavage, and the cleavage regulates VHL proteostasis and subsequent function. We characterized VHL species using genetical and pharmacological approaches and showed that VHL was first cleaved at the N-terminus by chymotrypsin C before being directed for proteasomal degradation. Casein kinase 2-mediated phosphorylation at VHL N-terminus was required for the cleavage. Furthermore, inhibition of cleavage stabilized VHL protein and thereby promoted HIF downregulation. Our study reveals a novel mechanism regulating VHL proteostasis and function, which is significant for identifying new drug targets and developing new therapeutic approaches targeting VHL deficiency in VHL diseases.