Germline mutations in the von Hippel-Lindau (VHL) tumor suppressor gene cause VHL disease, a rare and autosomaldominant genetic syndrome. Because VHL protein (pVHL) is the master regulator of hypoxia-inducible factor alpha (HIFa), the most prominent feature of VHL disease is the deregulation of HIFa proteins. However, the precise mechanism by which the loss of pVHL function contributes to tumorigenesis is not fully understood. Here, we show that pVHL destabilizes the F-box protein Skp2, a chief component of Skp, Cullin, F-box-containing complex that promotes DNA synthesis in the S phase. The b-domain of pVHL interacts with Skp2, stimulating proteasome-dependent Skp2 degradation, but the destabilization of Skp2 does not depend on the E3 ubiquitin ligase activity of pVHL. Notably, the generation of DNA damage induces Skp2 degradation, which is attenuated by the suppression of endogenous pVHL expression. One possible mechanism of pVHL-dependent Skp2 degradation entails the antagonizing of Akt-mediated Skp2 phosphorylation, which maintains Skp2 stability. Reintroduction of VHL into VHL-null renal cell carcinoma (RCC) cells decreased Skp2 levels and restored DNA damage-dependent Skp2 degradation. These results identify the tumor suppressor function of pVHL in delaying the S-phase progression to inhibit cell proliferation on DNA damage. Clinically, this report explains as to why Skp2 accumulates abnormally in RCC tissues.

AbstractpVHL is a tumor suppressor. The lack of its function leads to various tumors, among which ccRCC (clear cell renal cell carcinoma) has the most serious outcome due to its resistance to chemotherapies and radiotherapies. Although HIF promotes the progression of ccRCC, the precise mechanism by which the loss of VHL leads to tumor initiation remains unclear. We exploited two zebrafish vhl mutants, vhl and vll, and Tg(phd3::GFP)i144 fish to identify crucial functions of Vhl in tumor initiation. Through the mutant analysis, we found that the role of pVHL in DNA repair is conserved in zebrafish Vll. Interestingly, we also discovered that Hif activation strongly suppressed genotoxic stress induced DNA repair defects and apoptosis in vll and brca2 mutants and in the embryos lacking ATM activity. These results suggest the potential of HIF as a clinical modulator that can protect cells from accumulating DNA damage and apoptosis which can lead to cancers and neurodegenerative disorders.