Suppression of KSHV-induced angiopoietin-2 inhibits angiogenesis, infiltration of inflammatory cells, and tumor growth

Abstract

Kaposi's sarcoma (KS) is a highly angiogenic and inflammatory neoplasia. The angiogenic and inflammatory cytokine angiopoietin-2 (Ang-2) is strongly expressed in KS due to Kaposi's sarcoma-associated herpesvirus (KSHV) infection. In the present study, we determined how Ang-2 contributes to development of KS by using telomerase-immortalized human umbilical vein endothelial cells (TIVE) as a model, which become malignantly transformed and express increased levels of Ang-2 following KSHV infection. Ang-2 released from TIVE-KSHV cells induces tyrosine phosphorylation of Tie-2 receptor from both human and mouse endothelial cells and promotes angiogenesis in nude mice. Functional inhibition or expressional "knock-down" of Ang-2 in these cells blocks angiogenesis and inhibits tumor growth. Ang-2 suppression also reduces the numbers of infiltrating monocytes/macrophages in tumors. In transwell-based cell migration assays, Ang-2 indeed enhances migration of human monocytes in a dose-dependent manner. These results underscore a pivotal role of KSHV-induced Ang-2 in KS tumor development by promoting both angiogenesis and inflammation. Our data also suggest that selective drug targeting of Ang-2 may be used for treatment of KS.

Kaposi's sarcoma-associated herpesvirus infection promotes differentiation and polarization of monocytes into tumor-associated macrophages

“…We previously reported that KSHV infection of endothelial cells induces the angiogenic and inflammatory cytokine Ang-2 to promote migration and recruitment of monocytes into tumors. 12 In the present study, we found that KSHV infection of endothelial cells strongly induces expression and release of IL-6, IL-10, and IL-13 that individually and collectively promote differentiation and polarization of monocytes into TAMs. The KSHV-induced TAMs express well-known TAM-specific markers such as CD-163 and LGMN, promote angiogenesis, and significantly enhance tumor growth in nude mice.…”

“…We previously showed that KSHV infection of endothelial cells induces Ang-2 to promote migration and recruitment of monocytes into KS tumors. 12 We suspected that KSHV infection of endothelial cells induce additional cytokines that drive the recruited monocytes to differentiate and polarize into TAMs. To test this hypothesis, we infected human umbilical vein endothelial cells (HUVECs) with mock or purified recombinant KSHV, BAC16, 38 for various time points, followed by measurement of expression of TAM-promoting cytokines such as IL-4, IL-6, IL-10, IL-13, and M-CSF.…”

“…Indeed, we recently reported that KSHV infection of endothelial cells induces production and secretion of the angiogenic and inflammatory cytokine angiopoietin-2 (Ang-2), which promotes migration and recruitment of monocytes into KS tumors. 12 In addition, a recent study demonstrated that endothelial cells ectopically expressing KSHV vFLIP protein produce cytokines that remodel myeloid cells toward a "pro-tumor" phenotype. 13 Nevertheless, little is known on how KSHV acute infection of endothelial cells impacts monocytes, and the role of monocytes/macrophages on KS tumor development has never been studied.…”

Role of Angiopoietins in Development of Cancer and Neoplasia Associated with Viral Infection

“…Adding Ang-2 neutralization antibody into the Matrigel effectively blocked the angiogenic effect of KSHV-induced Ang-2. This data is concordant with a recent study using a KSHV-induced endothelial cell tumor model that strongly expressed Ang-2 [94,169]. When equal numbers of the KSHV-induced tumor cells were used in a Matrigel-based angiogenesis assay in nude mice, inclusion of AMG-138 or L1-10, two peptide-based Ang-2 inhibitors [81], substantially reduced the numbers of blood vessels.…”

“…One study demonstrated that administration of Ang-2, but not Ang-1, induced edema in the mouse paw in a dose-dependent manner [90], which was blocked by co-administration of soluble Tie-2. Both Ang-1 and Ang-2 demonstrated the abilities to attract migration of inflammatory cells such as neutrophils and monocytes [90][91][92][93][94]. Chemotaxis seems to be a driving force for Ang-1/Ang-2 mediated migration of inflammatory cells [92].…”