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HIV-1 viral protein R (Vpr) shuttles between the nucleus and the cytoplasm and is believed to contribute to the process of nuclear translocation of the viral preintegration complex, thus facilitating HIV-1 replication in macrophages. In this report, we demonstrate that Hsp70, a heatshock protein contributing to cellular stress responses, inhibits nuclear translocation of HIV-1 Vpr. In macrophages, Hsp70 is induced shortly after HIV-1 infection. Recombinant Hsp70 or a mild heat shock diminished replication of the wildtype HIV-1, suggesting that Hsp70 might function as an innate antiviral factor. Surprisingly, Hsp70 stimulated nuclear import and replication in macrophages of the Vpr-deficient HIV-1 construct. This finding suggests that Hsp70 and Vpr may function in a similar manner when expressed separately, but they neutralize each other's activity when present together. Consistent with this interpretation, Hsp70 coprecipitated with Vpr from