Heat-shock protein 70 is an innate immunity factor that antagonizes HIV-1 viral protein R

M. Bukrinsky¹, S. Iordanskiy¹, Y. Zhao²; ¹The George Washington University Medical Center, Washington, DC; ²The Northwestern University, Chicago, IL (USA)

Background: Heat shock protein 70 (Hsp70) is a member of a family of molecular chaperones that contribute to innate immunity and protection from environmental stress.  Heat-shock proteins Hsp27 and Hsp70 are selectively expressed early after HIV-1 infection, suggesting that expression of these proteins might be a part of the host innate antiviral immune responses.  However, the specific targets of heat shock proteins and their role in responses to HIV infection are still unclear. Material and Methods: The effect of Hsp70 on Vpr-induced apoptosis and G2 arrest was measured both in yeast and mammalian cells by FACS analysis.  Nuclear transport activity was analyzed using Vpr-PK-GFP construct provided by M. Sherman and W. Greene.  For Vpr and Hsp70 expression in mammalian cells, a muristerone A-inducible system was used.  HIV infections were performed using Vpr-positive and Vpr-defective NL4-3 strain pseudotyped with an envelope of an amphotropic MLV. Results: Here, we demonstrate that Hsp70 inhibits several activities of the HIV-1 viral protein R (Vpr), which contribute to HIV-1 pathogenesis.  Overexpression of Hsp70 reversed Vpr-induced G2 arrest, prevented death of Vpr-expressing cells, and inhibited nuclear translocation of Vpr.  In the context of HIV-1 infection of T lymphocytes, overexpressing the Hsp70 or adding recombinant Hsp70 protected infected cells from Vpr-induced growth arrest and apoptosis without affecting viral replication.  Surprisingly, neither Hsp70 nor heat shock protected macrophages from HIV-1 infection; instead, heat shock rescued nuclear import of the pre-integration complex and replication in macrophages of the Vpr-deficient HIV-1 construct. Conclusion: Our results demonstrate that Hsp70 functions as an innate immunity factor in protecting cells from Vpr-mediated G2 arrest and apoptosis.  Therefore, Hsp70 appears to be a component of the innate immunity against HIV-1.  However, Hsp70 does not suppress HIV-1 replication.  To our knowledge, this is the first example of a target protein for Hsp70-mediated activity during an innate immune response.  Mechanisms of Hsp70-mediated protection might be exploited in designing new therapeutic approaches to treat HIV-1 infection.