Anti-VBP1 monoclonal antibody, clone 3B4

MAP kinase-interacting kinase-2 (Mnk2) is one of the downstream kinases activated by MAP kinases. It phosphorylates the eukaryotic initiation factor 4E (elF4E), although the role of elF4E phosphorylation and the role of Mnk2 in the process of protein translation are not well understood. Except for elF4E, other physiological substrates of Mnk2 are still unidentified. To look for these unidentified substrates and to reveal the physiological function of Mnk2, we performed a yeast two-hybrid screening with Mnk2 as the bait. The results demonstrated Mnk2 could interact with VHL (von Hippel-Lindau tumor suppressor), Rbx1 (ring-box 1) and Cul2 (Cullin2) proteins in yeast cells. Furthermore, we validated the interaction between Mnk2 and VHL proteins in mammalian cells by co-immunoprecipitation analysis. Because the three proteins VHL, Rbx1 and Cul2 are all components of the CBCVHL ubiquitin ligase E3 complex, it has been shown that Mnk2 can interact with CBCVHL complex, and is probably one of the new substrates of the CBCVHL complex. Furthermore, during the interaction of Mnk2 with von Hippel-Linclau (VHL) tumor suppressor- binding protein 1 (VBP1), it appears that Mnk2 also joins to modulate cell shape as VBP1 plays an important role in the process of the maturation of the cytoskeleton and in the process of morphogenesis.

von Hippel-Lindau-binding protein 1 (VBP1) physically interacts with pVHL, an E3-ubiquitin ligase, which degrades HIF-1 alpha in an oxygen-dependent manner. HIF-1 is a key regulator of adaptive responses to a lack of oxygen that controls glucose metabolism, angiogenesis, proliferation, invasion, and metastasis. However, the role of VBP1 in pVHL-mediated degradation of HIF-1 alpha is not yet known. In this study, we show that VBP1 enhances the stability of pVHL and facilitates pVHL-mediated ubiquitination of HIF-1 alpha. Furthermore, VBP1 suppresses HIF-1 alpha-induced epithelial-mesenchymal transition in vitro and tumor metastasis in vivo. These findings suggest that VBP1 is a bona fide tumor suppressor protein associated with HIF-1 alpha regulation.