The Kaposi's sarcoma-associated herpesvirus G protein-coupled receptor promotes endothelial cell survival through the activation of Akt/protein kinase B

The Kaposi's sarcoma-associated herpesvirus G protein-coupled receptor (KSH V-GPCR) is a key molecule in the pathogenesis of Kaposi's sarcoma, playing a central role in the promotion of vascular endothelial growth factor (VEGF )-driven angiogenesis and spindle cell proliferation. We previously have sh own that KSHV-GPCR has oncogenic potential when overexpressed in fibroblast s and is responsible for the expression and secretion of VEGF through the r egulation of different intracellular signaling pathways (A, Sodhi ed nl., C ancer Res., 60: 4873-4880, 2000; C, Bais et al., Nature, 391: 86-89, 1998). Here, we describe that this constitutively active G protein-coupled recept or is able to promote cell survival in primary human umbilical vein endothe lial cells and that this effect is independent of its ability to secrete VE GF because it is not prevented by the expression of antisense constructs fo r VEGF or the addition of VEGF-blocking antibodies. Instead we found that e ctopic expression of KSHV-GPCR potently induces the kinase activity of Akt/ protein kinase E in a dose-dependent manner and triggers its translocation to the plasma membrane, This signaling pathway requires the function of pho sphatidylinositol 3 ' -kinase and is dependent on beta gamma subunits relea sed from both pertussis toxin-sensitive and -insensitive G proteins. Furthe rmore, we found that KSHV-GPCR is able to protect human umbilical vein endo thelial cells from the apoptosis induced by serum deprivation and that both wortmannin and the expression of a kinase-deficient Akt K179M mutant are a ble to block this effect. Finally, we observed that the AktK179M protein al so inhibits the activation of nuclear factor-kappaB induced by KSHV-GPCR, s uggesting that this transcription factor may represent one of the putative downstream targets for Akt in the survival-signaling pathway. These results provide further knowledge in the elucidation of the signal transduction pa thways activated by KSHV-GPCR and support its key role in promoting the sur vival of viral-infected cells. Moreover, the present findings also emphasiz e the importance of this G protein-coupled receptor in the development of K SHV-related neoplasias.