KSHV G-protein coupled receptor vGPCR oncogenic signaling upregulation of Cyclooxygenase-2 expression mediates angiogenesis and tumorigenesis in Kaposi's sarcoma

Kaposi’s sarcoma-associated herpesvirus (KSHV) vGPCR is a constitutively active G protein-coupled receptor that subverts proliferative and inflammatory signaling pathways to induce cell transformation in Kaposi’s sarcoma. Cyclooxygenase-2 (COX-2) is an inflammatory mediator that plays a key regulatory role in the activation of tumor angiogenesis. Using two different transformed mouse models and tumorigenic full KSHV genome-bearing cells, including KSHV-Bac16 based mutant system with a vGPCR deletion, we demostrate that vGPCR upregulates COX-2 expression and activity, signaling through selective MAPK cascades. We show that vGPCR expression triggers signaling pathways that upregulate COX-2 levels due to a dual effect upon both its gene promoter region and, in mature mRNA, the 3’UTR region that control mRNA stability. Both events are mediated by signaling through ERK1/2 MAPK pathway. Inhibition of COX-2 in vGPCR-transformed cells impairs vGPCR-driven angiogenesis and treatment with the COX-2-selective inhibitory drug Celecoxib produces a significant decrease in tumor growth, pointing to COX-2 activity as critical for vGPCR oncogenicity in vivo and indicating that COX-2-mediated angiogenesis could play a role in KS tumorigenesis. These results, along with the overexpression of COX-2 in KS lesions, define COX-2 as a potential target for the prevention and treatment of KSHV-oncogenesis.
Author summary Kaposi sarcoma (KS) is the most frequent AIDS-related cancer (AIDS-KS). The tumors originate in cells infected with a cancer-causing virus (KSHV). A gene encoded by the virus expresses a protein with oncogenic potential in the infected cells (vGPCR), which has the ability to promote cell transformation and angiogenesis driving KS tumorigenesis. Therefore, the identification of oncogenic intracellular signalling mechanisms triggered by vGPCR could be of therapeutic interest. Cyclooxygenase-2 (COX-2) is an inflammatory molecule involved in tumor angiogenesis that can be targeted by several FDA-approved non-steroidal anti-inflammatory drugs and specific inhibitors. Here, we demonstrate that vGPCR upregulates COX-2 activity and expression through upregulation of transcription and mRNA stability via an ERK1/2 dependent pathway. We also show that COX-2 activity is critical for vGPCR angiogenesis and oncogenesis using KSHV infection and mouse models. Consistent with a role in KS pathogenesis, we found that vGPCR upregulates COX-2 activity in endothelial cells, that it is essential for VEGF upregulation via vGPCR, and that it is expressed in KSHV infected cells of AIDS-KS lesions. These facts point to COX-2 as one of the molecular components of the vGPCR angiogenic switch in Kaposi Sarcoma and a potential target for chemoprevention and therapy.