Loss of E-Cadherin Promotes Ovarian Cancer Metastasis via α5-Integrin, which Is a Therapeutic Target

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Abstract
E-cadherin loss is frequently associated with ovarian cancer metastasis. Given that adhesion to the abdominal peritoneum is the first step in ovarian cancer dissemination, we reasoned that down-regulation of E-cadherin would affect expression of cell matrix adhesion receptors. We show here that inhibition of E-cadherin in ovarian cancer cells causes up-regulation of α5-integrin protein expression and transcription. When E-cadherin was blocked, RMUG-S ovarian cancer cells were able to attach and invade more efficiently. This greater efficiency could, in turn, be inhibited both in vitro and in vivo with an α5β1-integrin–blocking antibody. When E-cadherin is silenced, α5-integrin is up-regulated through activation of an epidermal growth factor receptor/FAK/Erk1–mitogen-activated protein kinase–dependent signaling pathway and not through the canonical E-cadherin/β-catenin signaling pathway. In SKOV-3ip1 ovarian cancer xenografts, which express high levels of α5-integrin, i.p. treatment with an α5β1-integrin antibody significantly reduced tumor burden, ascites, and number of metastasis and increased survival by an average of 12 days when compared with IgG treatment (P < 0.0005). α5-Integrin expression was detected by immunohistochemistry in 107 advanced stage ovarian cancers using a tissue microarray annotated with disease-specific patient follow-up. Ten of 107 tissues (9%) had α5-integrin overexpression, and 39% had some level of α5-integrin expression. The median survival for patients with high α5-integrin levels was 26 months versus 35 months for those with low integrin expression (P < 0.05). Taken together, we have identified α5-integrin up-regulation as a molecular mechanism by which E-cadherin loss promotes tumor progression, providing an explanation for how E-cadherin loss increases metastasis. Targeting this integrin could be a promising therapy for a subset of ovarian cancer patients. [Cancer Res 2008;68(7):2329–39]