Activation of p21-activated kinase 1-nuclear factor κB signaling by Kaposi's sarcoma-associated herpes virus G protein-coupled receptor during cellular transformation

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- Kappa B (NF Kappa B) is required for cell transformation induced by KSHV-GPCR. KSHV-GPCR induced transcriptional activation by NF Kappa B. This process is inhibited by the PAK-PID, whereas reciprocally, expression of constitutively active Pak1 (PakL107F) activated NF Kappa B comparably to KSHV-GPCR. The Pak-PID and RacN17 inhibited the KSHV-GPCR-induced phosphorylation of inhibitor of Kappa B kinase- beta and inhibitor of Kappa B- alpha , implying that it is Pak1-dependent phosphorylation and subsequent destruction of the inhibitor of Kappa B proteins that allows NF Kappa B activation. Finally, experiments with the KSHV-GPCR inverse agonist interferon- gamma -inducible protein-10, the G alpha sub(i) inhibitor pertussis toxin, and an inhibitor of phosphatidylinositol 3'-kinase, wortmannin, indicate that signaling through the G alpha sub(i) pathway and phosphatidylinositol 3'-kinase contributes to the cell transformation and NF Kappa B activation induced by the KSHV-GPCR.