Constitutive activation of NF-κB and secretion of interleukin-8 induced by the G protein-coupled receptor of Kaposi's sarcoma-associated herpesvirus involve Gα13 and RhoA

The Kaposi's sarcoma herpesvirus (KSHV) open reading frame 74 encodes a G protein-coupled receptor (GPCR) for chemokines. Exogenous expression of this constitutively active GPCR leads to cell transformation and vascular overgrowth characteristic of Kaposi's sarcoma. We show here that expression of KSHV-GPCR in transfected cells results in constitutive transactivation of nuclear factor kappaB (NF-kappaB) and secretion of interleukin-8, and this response involves activation of Gals and RhoA. The induced expression of a NF-kappaB luciferase reporter was partially reduced by pertussis toxin and the G beta gamma scavenger transducin, and enhanced by co-expression of Gals and to a lesser extent, G alpha (q). These results indicate coupling of KSHV-GPCR to multiple G proteins for NF-kappaB activation. Expression of KSHV-GPCR led to stress fiber formation in NIH 3T3 cells. To examine the involvement of the G alpha (13)-RhoA pathway in KSHV-GPCR-mediated NF-kappaB activation, HeLa cells were transfected with KSHV-GPCR alone and in combination with the regulator of G protein signaling (RGS) from p115RhoGEF or a dominant negative RhoA(T19N). Both constructs, as well as the C3 exoenzyme from Clostritium botulinum, partially reduced NF-kappaB activation by KSHV-GPCR, and by a constitutively active G alpha (13)(Q226L). KSHV-GPCR-induced NF-kappaB activation is accompanied by increased secretion of IL-8, a function mimicked by the activated G alpha (13) but not by an activated G alpha (q)(Q209L). These results suggest coupling of KSHV-GPCR to the G alpha (13)-RhoA pathway in addition to other G proteins.