Background:  HIV-associated nephropathy (HIVAN) is the leading cause of end-stage renal disease in the HIV-1-seropositive community, affecting an estimated 1 million to 3 million people worldwide. Murine transgenic models of HIVAN indicate that renal expression of HIV-1 vpr plays a role in disease development but the mechanism is unknown. Since vpr has been implicated in a variety of in vitro phenotypes—including immune modulation, apoptosis, and cell cycle arrest—we hypothesized that the renal proximal tubule epithelium may be similarly adversely affected. 

Methods:  The HK2 cell line was used as a model of human renal proximal tubule epithelium. Cells were transduced using a pseudotyped lentivirus system carrying individual HIV-1 genes or transduced with control empty vectors. Cells were analyzed for morphology, proliferation, and cell cycle progression. Cell cycle analysis was performed by flow cytometry and propidium iodide staining. Immunoblotting for PARP-1 cleavage was used to detect apoptosis.

Results:  HIV-1 vpr induces G2 cell cycle arrest and apoptosis in cultured human proximal tubule cells (HK2 line). HK2 cells expressing the HIV-1 proteins vif or tat were indistinguishable from control cells transduced with empty vectors despite reports of arrest and apoptosis in other cell types. Furthermore, the vpr mutant vpr-R80A, containing a single amino acid change and previously reported as abrogating cell cycle arrest and apoptosis in CD⁺ T cells, does not induce phenotypic changes in HK2 cells. Chk1 phosphorylation was increased in the vpr arrested cells implicating activation of the ATR DNA damage response pathway as a mechanism for this arrest.

Conclusions:  HIVAN pathogenesis is associated with viral infection, integration, and gene expression in glomerular and tubular epithelial cells. This study is the first direct evidence that HIV-1 vpr induces G2 arrest and apoptosis in renal proximal tubule epithelial cells and that this mechanism may contribute to HIVAN pathogenesis in vivo.