Gα13 mediates human cytomegalovirus-encoded chemokine receptor US28-induced cell death in melanoma

Abstract

US28, a constitutively active G-protein-coupled receptor encoded by the human cytomegalovirus, leads to mechanistically unknown programmed cell death. Here we show that expression of wild type US28 in human melanoma cells leads to apoptotic cell death via caspase 3 activation along with reduced cell proliferation. Reduced tumor growth upon US28 expression was observed in a xenograft mouse model. The signaling mute US28R129A showed a reduced anti-proliferative effect. On evaluating different G-proteins coupled to US28 for signal transduction, Gα13 was identified as the main G-protein executing the apoptotic effect. Silencing of Gα13 but not Gαq resulted in a substantial increase in cell survival. Over-expression of Gα13 but not Gαq and their GTPase deficient forms Gα13Q226L and GαqQ209L, respectively, confirmed the requirement of Gα13 for US28 mediated cell death. Increasing expression of Gα13 alone induced cell death underscoring its relay function for US28 mediated decreased cell viability. Further reduced expression of Gα13 in melanoma cell lines isolated from advanced lesions and melanoma tissue was observed. These findings identified Gα13 as crucial for US28 induced cell death, substantiating that the effect of US28 on cell fate depends on preferred G-protein binding.

Viral G protein-coupled receptors as modulators of cancer hallmarks

“…US28-expressing LoVo colon cancer cells are less sensitive to cisplatin treatment, indicating enhanced cell death resistance via US28 [53]. In contrast, US28 is also known to induce apoptosis, when expressed at elevated levels for example in COS-7, HeLa, HEK293T and melanoma cells [118,119]. This indicates that regulation of cell death and survival by US28 is strongly dependent on the cell type.…”

The HCMV US28 vGPCR induces potent Gαq/PLC-β signaling in monocytes leading to increased adhesion to endothelial cells

“…In the canonical Gαq signaling pathway, Gαq can activate phospholipase C-β to induce inositol triphosphate (IP 3 ) accumulation, which leads to the release of calcium from the endoplasmic reticulum (ER) and the activation of protein kinases such as Protein Kinase C (PKC) (Rozengurt, 2007). In addition to Gαq, other Gα subunits including Gα12, Gα13, Gα16, and Gαi have been shown to be involved in US28-dependent constitutive and/or ligand-dependent signaling (Billstrom et al, 1998; Joshi et al, 2015; Melnychuk et al, 2004; Moepps et al, 2008). However, whether or not US28 triggers a similar or distinct set of signaling pathways in monocytes remains unexplored.…”

Gα12 and Gα13: Versatility in Physiology and Pathology

“…In Madin-Darby canine kidney cells, the activation of endogenous Gα 12 and thrombin stimulation increase the activity of JNK1, inhibit the activity of NF-κB, and promote cell apoptosis ( Yanamadala et al, 2007 ). In melanoma cells, US28, a GPCR encoded by human cytomegalovirus, is coupled with Gα 13 to induce cell apoptosis; silencing Gα 13 inhibits cell apoptosis driven by US28 ( Joshi et al, 2015 ). Notably, this event has been only observed in human melanoma cell lines but not in murine cells.…”