Mechanism of Angiopoietin-1 Upregulation in Kaposi's Sarcoma-Associated Herpesvirus-Infected PEL Cell Lines

Abstract

Angiopoietin-1 (ANGPT-1) is a secreted glycoprotein that was first characterized as a ligand of the Tie2 receptor. In a previous study using microarray analysis, we found that the expression of ANGPT-1 was upregulated in Kaposi's sarcoma-associated herpesvirus (KSHV)-infected primary effusion lymphoma (PEL) cell lines compared with that in uninfected Burkitt and other leukemia cell lines. Other authors have also reported focal expression of ANGPT-1 mRNA in biopsy specimens of Kaposi's sarcoma (KS) tissue from patients with AIDS. Here, to confirm these findings, we examined the expression and secretion levels of ANGPT-1 in KSHV-infected PEL cell lines and address the mechanisms of ANGPT-1 transcriptional regulation. We also showed that ANGPT-1 was expressed and localized in the cytoplasm and secreted into the supernatant of KSHV-infected PEL cells. Deletion studies of the regulatory region revealed that the region encompassing nucleotides ؊143 to ؊125 of the ANGPT-1-regulating sequence was responsible for this upregulation. Moreover, an electrophoretic mobility shift assay and chromatin immunoprecipitation, followed by quantitative PCR, suggested that some KSHV-infected PEL cell line-specific DNA-binding factors, such as OCT-1, should be involved in the upregulation of ANGPT-1 in a sequence-dependent manner. IMPORTANCEWe confirmed that ANGPT-1 was expressed in and secreted from KSHV-infected PEL cells and that the transcriptional activity of ANGPT-1 was upregulated. A 19-bp fragment was identified as the region responsible for ANGPT-1 upregulation through binding with OCT-1 as a core factor in PEL cells. This study suggests that ANGPT-1 is overproduced in KSHV-infected PEL cells, which could affect the pathophysiology of AIDS patients with PEL. K aposi's sarcoma (KS)-associated herpesvirus (KSHV), also known as human herpesvirus 8, belongs to the gamma-2 herpesvirus family, which was first identified in KS lesions (1). Epstein-Barr virus (EBV), which also belongs to the gamma-2 herpesvirus family, is frequently associated with malignancies such as Burkitt lymphoma (BL) and nasopharyngeal carcinoma (NPC) (2). KSHV is also associated with several malignancies, i.e., two lymphoproliferative disorders, primary effusion lymphoma (PEL) (3) and multicentric Castleman's disease, as well as KS (4, 5).It has been reported that KSHV infects various cell types, such as B cells, blood vessel endothelial cells (BECs), lymphatic endothelial cells (LECs), Vero cells, and HEK293 cells (6-9). After infection, KSHV utilizes latency as a default pathway of replication (1, 7). Though viral gene expression profiles might differ between BECs and LECs (10), KSHV is predominantly in latency with its genome binding to the host cell chromosome (10, 11) and governs host gene expression profiles (12) as other viruses do (13, 14). Most KSHV-infected cells are latently infected, and only a limited number of viral genes are expressed in latency: latency-associated nuclear antigen (LANA), viral cyclin (vCYC), viral FLICE inhibitory prote...

KSHV-Mediated Angiogenesis in Tumor Progression

“…Ang-1 is ubiquitously expressed in endothelial cells, whereas Ang-2 has been found to be upregulated at the sites of vascular remodeling [ 25 , 100 , 102 , 103 ]. Recently, a study from Keiji Ueda’s group reported that DNA binding factors, including octamer-binding transcription factor (OCT1), play a key role in the upregulation of ANGPT-1 transcriptional activity in PEL cells [ 104 ], further indicating that cellular micro environments created by KSHV infection are most probably due to the upregulation of ANGPT-1 expression and may directly contribute to the disease progression in AIDS patients with PEL [ 104 ].…”

Landscape and Targeting of the Angpt-Tie System in Current Anticancer Therapy

“…As archived in most literature, Angpts are usually expressed by pericytes and secreted to the extracellular matrix (ECM), whereby contributing to neovascularization in the TME niches. However, recent studies revealed that Angpt1 is upregulated in Kaposi's sarcomaassociated herpesvirus (KSHV)-infected primary effusion lymphoma (PEL) cell lines, with the expression level higher than that in uninfected lymphoma or leukemia cell lines [47]. The reason is, some KSHVinfected PEL cell line-specific DNA-interacting factors, such as Oct 1, binds to the Angpt1 promoter region (-143 to -125) thereby regulating its expression.…”