Analysis of apoptosis induced by HIV-1 Vpr and examination of the possiblerole of the hHR23A protein

The HIV-1 Vpr protein induces apoptosis of cells, the mechanism of which is unknown. To clarify how this function may be related to other Vpr function s, we simultaneously assessed the effects of multiple point mutations upon various Vpr properties. Our data suggest that induction of arrest by Vpr ma y be unnecessary for induction of apoptosis. This is exemplified by a C-ter minal mutant, R80A, that does not arrest cells, yet induces low but signifi cant levels of apoptosis. We also show that mutation of Vpr at both of its nuclear localization sequences (within its a-helices and the overlapping le ucine zipper-like domain) does not affect induction of either apoptosis or cell cycle arrest. This indicates that neither sequence is essential for th ese two functions of Vpr. It further suggests that multimerization of Vpr, which maps to residues 60 and 67 within the leucine-rich region, is unneces sary for initiation of apoptosis and arrest. We previously found that the V pr-binding protein, hHR23A, can partially alleviate induction of arrest. We now show that overexpression of hHR23A itself causes apoptosis of cells. M utation of its C-terminal UBA(2) domain that is responsible for binding Vpr disrupts the apoptotic effect. This suggests that Vpr may induce apoptosis through a pathway involving hHR23A. (C) 2001 Academic Press.