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HIV-1 Nef associated PAK and PI3-Kinases stimulate Akt-independent Bad-phosphorylation to induce anti-apoptotic signals

Abstract

A highly conserved signaling property of Nef proteins encoded by human or simian immunodeficiency virus is the binding and activation of a PAK kinase whose function is unclear. Here we show that Nef-mediated p21-activated kinase (PAK) activation involves phosphatidylinositol 3-kinase, which acts upstream of PAK and is bound and activated by Nef similar to the manner of Polyoma virus middle T antigen. The Nef-associated phosphatidylinositol-3–PAK complex phosphorylated the pro-apoptotic Bad protein without involving the protein kinase B–Akt kinase, which is generally believed to inactivate Bad by serine phosphorylation. Consequently, Nef, but not a Nef mutant incapable of activating PAK, blocked apoptosis in T cells induced by serum starvation or HIV replication. Nef anti-apoptotic effects are likely a crucial mechanism for viral replication in the host and thus in AIDS pathogenesis.

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Figure 1: Binding and activation of PI3-kinase by HIV-1, Nef and Polyoma mTAg.
Figure 2: Nef protects cells from apoptosis induced by serum starvation.
Figure 3: Polyoma mTAg but not Nef induces phosphorylation of PKB/Akt.
Figure 4: Nef induces Bad phosphorylation via PAK, which acts downstream of PI3-kinase.
Figure 5: Bad is phosphorylated in HIV-infected cells in a Nef/PI3-K/PAK–dependent manner.
Figure 6: Nef blocks apoptosis in HIV-infected cells and increases viral particle release.

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Acknowledgements

We thank K. Saksela, M. Peterlin, M. Lutz and J.-O. Funk for critical reading of the manuscript and discussions; S. Lang for providing the Jurkat CD4+ cell line; M. Harris and A. Klippel for providing antibodies against Nef and p85; K. Ballmer-Hofer, M. Peterlin and K. Saksela for providing expression plasmids; P. Thumann for technical assistance; and B. Fleckenstein and G. Schuler for their support of this study. This work was supported by the Deutsche Forschungsgemeinschaft (DFG), Sonderforschungsbereich (SFB) 466.

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Correspondence to Andreas S. Baur.

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Wolf, D., Witte, V., Laffert, B. et al. HIV-1 Nef associated PAK and PI3-Kinases stimulate Akt-independent Bad-phosphorylation to induce anti-apoptotic signals. Nat Med 7, 1217–1224 (2001). https://doi.org/10.1038/nm1101-1217

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