The significance of GRO-α and IL-8 in promoting omental metastasis of ovarian cancer

Abstract

Ovarian cancer is one of the leading causes of cancer-related death in females. Cancer metastasis is the major reason for the resultant mortality of patients with this disease. Different from other cancers, transcoelomic metastasis is the most common route in ovarian cancer. Within the peritoneal cavity, the omentum is the most preferential tissue for metastatic ovarian cancer cells. However, this organ is rarely studied, and the underlying molecular mechanisms for the tumor microenvironment of the omentum involved in ovarian cancer cell colonization remain obscure. Omentum-conditioned medium (OCM) mimicking the omental tumor microenvironment has been shown to promote ovarian cancer cell tumorigenecity via TAK1/NFκB pathway previously. Cytokine array profiling revealed that IL-8 and GRO-α are the key chemokines in OCMs activating TAK1/NFkB signaling and the associated ovarian cancer aggressiveness. In this study, ELISA showed that IL-8 and GRO-α are highly expressed in OCMs derived from either normal or cancerous omenta. Immunohistochemical analysis (IHC) further displayed that GRO-α originates mainly from milky spots, lymph nodes, blood vessels and adipocytes in the omentum, whereas the majority of IL-8 originates from ovarian cancer cells and some from omental tissues. This manifests that a positive feedback loop of IL-8 secretion is bridging between tumor cells and cancerous omental tissues.

On the other hand, ovarian cancer cells showed an increase of cell proliferation, cell migration and invasion when cultured with either IL-8 or GRO-α dose dependently. The metastatic ovarian cancer cells isolated from the omentum particularly showed more aggressive when cultured in OCM as compared with primary ovarian tumor cells. Consistently, TAK1/NFκB signaling activity was higher in metastatic ovarian cancer cells, indicating the intrinsic oncogenic properties of metastatic cancer cells confer OCM-induced TAK1/NFκB signaling. Indeed, the cDNA microarray profiling revealed that the NFκB-associated angiogenesis pathway is upregulated in the metastatic cancer cells. In contrast, the activated TAK1/NFκB signaling could be attenuated by GRO-α and IL-8 neutralizing antibodies, suggesting these chemokines play a crucial role in governing the oncogenic tumor microenvironment facilitating ovarian cancer cell colonization in the omentum. Moreover, using neutralizing antibody or specifically knockdown of CXCR2 (the common receptor of both GRO-α and IL-8) could significantly inhibit OCM-induced activation of TAK1/NFκB signaling and the associated tumor cell aggressiveness. Taken together, this study suggests that GRO-α and IL-8 are the key chemokines in OCM secreted from omental tissues in promoting ovarian cancer cell aggressiveness via modulating CXCR2/TAK1/NFκB signaling cascade.