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Activation of p21-Activated Kinase 1-Nuclear Factor B Signaling by Kaposi’s Sarcoma-Associated Herpes Virus G Protein-Coupled Receptor during Cellular Transformation

¹ Department of Pharmacology, University of Pennsylvania, School of Medicine, Philadelphia, Pennsylvania, and
² Division of Basic Science, Fox Chase Cancer Center, Philadelphia, Pennsylvania

Kaposi’s sarcoma-associated herpes virus (KSHV) contributes to the pathogenesis of Kaposi’s sarcoma and primary effusion lymphomas. KSHV encodes a G protein-coupled receptor (KSHV-GPCR) that signals constitutively and transforms NIH3T3 cells. Here, we show that KSHV-GPCR transformation requires activation of the small G protein Rac1 and its effector, the p21-activated kinase 1 (Pak1). Either transient or sustained expression of KSHV-GPCR activated both Rac1 and Pak1. Furthermore, expression of dominant-negative mutants of Rac (RacN17) or Pak1 (PakR299, Pak-PID) inhibited KSHV-GPCR-induced focus formation and growth in soft agar. We also demonstrate that signaling from Pak1 to nuclear factor-B (NFB) is required for cell transformation induced by KSHV-GPCR. KSHV-GPCR induced transcriptional activation by NFB. This process is inhibited by the PAK-PID, whereas reciprocally, expression of constitutively active Pak1 (PakL107F) activated NFB comparably to KSHV-GPCR. The Pak-PID and RacN17 inhibited the KSHV-GPCR-induced phosphorylation of inhibitor of B kinase-ß and inhibitor of B-, implying that it is Pak1-dependent phosphorylation and subsequent destruction of the inhibitor of B proteins that allows NFB activation. Finally, experiments with the KSHV-GPCR inverse agonist interferon--inducible protein-10, the G_i inhibitor pertussis toxin, and an inhibitor of phosphatidylinositol 3'-kinase, wortmannin, indicate that signaling through the G_i pathway and phosphatidylinositol 3'-kinase contributes to the cell transformation and NFB activation induced by the KSHV-GPCR.

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