Abstract
Ubiquitination is an important mechanism for the regulation of diverse cellular functions, including proteolysis and DNA repair. The human MutS family protein hMSH4 functions in meiotic recombinational DNA double-strand break (DSB) repair. It was previously observed that hMSH4 interacts with the von Hippel-Lindau binding protein 1 (VBP1), a partner of the VHL ubiquitin E3 ligase as well as a subunit of the prefoldin complex. In this study we address how ubiquitination regulates the homeostasis of hMSH4 in the human embryonic kidney cell line HEK293T. We demonstrate that VBP1 targets hMSH4 for degradation and identify a new VBP1 binding partner, p97, an AAA(+) ATPase involved in protein degradation and DNA damage response. VBP1, VHL, and p97 coexist in the hMSH4 immunocomplex and regulate the polyubiquitination of hMSH4. Furthermore, the results of this study demonstrate that VBP1 acts together with p97 to regulate hMSH4 degradation. Overall, this study has revealed a molecular mechanism by which VBP1 controls the levels of hMSH4 by ubiquitination in mitotic cells. Such a mechanism may be important for controlling the role of hMSH4 in regulating homologous recombination and nonhomologous DNA end joining-mediated DSB repair in human cells.