G-protein-coupled receptor of Kaposi's sarcoma-associated herpesvirus is a viral oncogene and angiogenesis activator.

The Kaposi's sarcoma-associated herpesvirus (KSHV/HHV8) is a gamma-2 herpesvirus that is implicated in the pathogenesis of Kaposi's sarcoma and of primary effusion B-cell lymphomas (PELs). KSHV infects malignant and progenitor cells of Kaposi's sarcoma and PEL, it encodes putative oncogenes and genes that may cause Kaposi's sarcoma pathogenesis by stimulating angiogenesis. The G-protein-coupled receptor encoded by an open reading frame (ORF 74) of KSHV is expressed in Kaposi's sarcoma lesions and in PEL and stimulates signalling pathways linked to cell proliferation in a constitutive (agonist-independent) way. Here we show that signalling by this KSHV G-protein-coupled receptor leads to cell transformation and tumorigenicity, and induces a switch to an angiogenic phenotype mediated by vascular endothelial growth factor, an angiogenesis and Kaposi's-spindle-cell growth factor. We find that this receptor can activate two protein kinases, JNK/SAPK and p38MAPK, by triggering signalling cascades like those induced by inflammatory cytokines that are angiogenesis activators and mitogens for Kaposi's sarcoma cells and B cells. We conclude that the KSHV G-protein-coupled receptor is a viral oncogene that can exploit cell signalling pathways to induce transformation and angiogenesis in KSHV-mediated oncogenesis.

Evidence that cobalt ion inhibition of prolactin secretion occurs at an intracellular locus.

Cobalt inhibition of stimulated prolactin secretion has been interpreted as demonstrating an essential role for enhanced calcium influx in the action of thyrotropin-releasing hormone (TRH) in GH3 cells. However, this interpretation is based on the assumption that cobalt ion (Co2+) binds to the external surface of cells to antagonize calcium-mediated processes only by blocking influx of extracellular calcium ion (Ca2+). In this report, we present evidence that Co2+ acts at an intracellular locus (or loci) to inhibit prolactin secretion. When GH3 cells were incubated in medium containing 1.5 mM Ca2+, Co2+ inhibited basal as well as 50 mM K+- and TRH-induced secretion; half-maximal effect occurred between 0.1 and 0.3 mM Co2+. When cells were incubated in medium containing 0.05 and 0.003 mM Ca2+, concentrations that abolish 50 mM K+-induced prolactin secretion, Co2+ still inhibited basal and TRH-stimulated prolactin secretion. Co2+ also inhibited prolactin secretion stimulated by 1-methyl-3-isobutylxanthine, dibutyryl adenosine 3',5'-cyclic monophosphate (cAMP), and vasoactive intestinal peptide, three secretagogues that act to elevate intracellular cAMP, a mechanism which appears not to involve enhanced Ca2+ influx. Last, the presence of Co2+ within the cell was shown by fluorescence quenching of intracellularly trapped Quin 2, a chelator of divalent cations. These data demonstrate that Co2+ enters GH3 cells and that Co2+ inhibition of prolactin secretion does not involve extracellular Ca2+. We suggest that Co2+ not only blocks Ca2+ channels in GH3 cells, but it inhibits prolactin secretion at an intracellular locus (loci). Hence, inhibition by Co2+ should not be interpreted as demonstrating a requirement for Ca2+ influx in stimulated secretion.