HIP1R interacts with a member of Bcl-2 family, BCL2L10, and induces BAK-dependent cell death

The Bcl-2 family members are evolutionally conserved and crucial regulators of apoptosis. BCL2L10 (human Diva or BCL-B) is a member of the Bcl-2 family that has contradictory functions in apoptosis. In the present study, we identified the Huntington-interacting protein 1-related (HIP1R) protein following a search for Diva-interacting proteins using the yeast two-hybrid system. HIP1R is a multi-domain protein that regulates the clathrin-mediated endocytic machinery and actin assembly in cells. Interaction of endogenous proteins of BCL2L10 and HIP1R in 293T cells was determined by immunoprecipitation, and their direct association was confirmed by the Far-Western analysis. The deletion of both the AP180-homology (ANTH) and F-actin-binding the talin-HIP1/R/Sla2p actin-tethering C-terminal homology (THATCH) domains of HIP1R greatly compromised its binding ability to BCL2L10. Ectopic expression of HIP1R resulted in moderate cell death of 293T cells in conjunction with the dissipation of mitochondrial membrane potential and caspase 9 activation. A member of proapoptotic Bcl-2 family, BAK, was required for HIP1R to induce cell death, while BAX was dispensable. In addition, BCL2L10 was associated with endogenous caspase 9, and their binding was augmented by HIP1R overexpression. Thus, this study provided the previously unknown function of HIP1R involved in the intrinsic cell death pathway and further explored possible mechanisms by which HIP1R induces cell death.