Cancer cells promote survival through depletion of the von Hippel-Lindau tumor suppressor by protein crosslinking

Nuclear factor-B (NF-B) and insulin-like growth factor-1 (IGF-1)-mediated signaling is associated with different tumors including renal cell carcinoma. NF-κB- and IGF-1-mediated signaling is found to be inhibited in the presence of wild-type von Hippel-Lindau (VHL) tumor suppresser gene. Therefore, negative regulator of VHL may be a good target for regulating NF-κB and IGF-1R. In this study, we found that VHL, a tumor suppressor protein that downregulates the NF-B activity and the stability of IGF-1R was depleted by TGase 2 through polymerization via crosslinking and proteasomal degradation in kidney, breast and ovary cancer cell lines. We also found that TGase 2 knockdown promotes hypoxia-inducible factor 1α (HIF-1α) degradation, and thereby decrease HIF-1α transcriptional activity. Importantly, VHL expression was decreased in vivo in TGase-2-transgenic mice, and this was associated with increased NF-κB activity and the levels of expression of IGF-1R, HIF-1α and erythropoietin in kidney tissue. These results suggest a novel mechanism of regulation of the VHL tumor suppressor by TGase 2 that appears to be independent of the known cancer regulatory mechanisms.