Glutamate Secretion and Metabotropic Glutamate Receptor 1 Expression during Kaposi's Sarcoma-Associated Herpesvirus Infection Promotes Cell Proliferation

Abstract

Kaposi's sarcoma associated herpesvirus (KSHV) is etiologically associated with endothelial Kaposi's sarcoma (KS) and B-cell proliferative primary effusion lymphoma (PEL), common malignancies seen in immunocompromised HIV-1 infected patients. The progression of these cancers occurs by the proliferation of cells latently infected with KSHV, which is highly dependent on autocrine and paracrine factors secreted from the infected cells. Glutamate and glutamate receptors have emerged as key regulators of intracellular signaling pathways and cell proliferation. However, whether they play any role in the pathological changes associated with virus induced oncogenesis is not known. Here, we report the first systematic study of the role of glutamate and its metabotropic glutamate receptor 1 (mGluR1) in KSHV infected cell proliferation. Our studies show increased glutamate secretion and glutaminase expression during de novo KSHV infection of endothelial cells as well as in KSHV latently infected endothelial and B-cells. Increased mGluR1 expression was detected in KSHV infected KS and PEL tissue sections. Increased c-Myc and glutaminase expression in the infected cells was mediated by KSHV latency associated nuclear antigen 1 (LANA-1). In addition, mGluR1 expression regulating host RE-1 silencing transcription factor/neuron restrictive silencer factor (REST/NRSF) was retained in the cytoplasm of infected cells. KSHV latent protein Kaposin A was also involved in the over expression of mGluR1 by interacting with REST in the cytoplasm of infected cells and by regulating the phosphorylation of REST and interaction with β-TRCP for ubiquitination. Colocalization of Kaposin A with REST was also observed in KS and PEL tissue samples. KSHV infected cell proliferation was significantly inhibited by glutamate release inhibitor and mGluR1 antagonists. These studies demonstrated that elevated glutamate secretion and mGluR1 expression play a role in KSHV induced cell proliferation and suggest that targeting glutamate and mGluR1 is an attractive therapeutic strategy to effectively control the KSHV associated malignancies.

HACE1, an E3 Ubiquitin Protein Ligase, Mitigates Kaposi’s Sarcoma-Associated Herpesvirus Infection-Induced Oxidative Stress by Promoting Nrf2 Activity

“…Earlier studies have shown the crucial roles of several KSHV latent proteins in regulating cellular processes to make the environment conducive to viral infection (26,41,44). We have previously shown that kaposin A, which is one of the proteins expressed during KSHV latency, played crucial roles in KSHV-induced cell proliferation by activating metabotropic glutamate receptor 1 (mGluR1) during KSHV infection (41). Kaposin A has also been shown to mediate oncogenesis in vitro in Rat3 fibroblasts and in nude mice (45,46).…”

“…Higher expression of HACE1 during de novo infection of endothelial cells, in KSHV latently infected TIVE-LTC and BCBL-1 cells as well as in the KS tissues, suggests that HACE1 is important for the biology of KSHV. Earlier studies have shown the crucial roles of several KSHV latent proteins in regulating cellular processes to make the environment conducive to viral infection (26,41,44). We have previously shown that kaposin A, which is one of the proteins expressed during KSHV latency, played crucial roles in KSHV-induced cell proliferation by activating metabotropic glutamate receptor 1 (mGluR1) during KSHV infection (41).…”

“…Lentiviral constructs for KSHV ORF71 (vFLIP), ORF72 (vCyclin), ORF73 (LANA-1), and ORFK12 (kaposin A) were a gift from Chris Boshoff at the UCL Cancer Institute. These were utilized for lentivirus production and transduction as described previously (41,67). siRNA transfection.…”

“…Glutamine plays an important role during oxidative stress, as it is metabolized to generate NADPH and glutamate, which is required for the synthesis of antioxidant glutathione (40). Increased glutamate secretion and glutaminase expression were observed in KSHV de novo-infected endothelial cells as well as in KSHV latently infected endothelial and B cells (41). Latent KSHV infection led to increased levels of intracellular glutamine and enhanced glutamine uptake, and further depletion of glutamine in culture medium led to cellular apoptosis (42).…”

ESCRT-0 Component Hrs Promotes Macropinocytosis of Kaposi's Sarcoma-Associated Herpesvirus in Human Dermal Microvascular Endothelial Cells

“…Subcellular fractionation and cell membrane preparation were performed as described previously (18,35). Briefly, cells were homogenized with a Dounce homogenizer in homogenization buffer (250 mM sucrose, 20 mM HEPES, 10 mM KCl, 1 mM EDTA, 1 mM EGTA, and protease inhibitors).…”