Data from ADAM23 Negatively Modulates α<sub>v</sub>β<sub>3</sub> Integrin Activation during Metastasis

The ADAM23 gene is frequently silenced in different types of tumors, and, in breast tumors, silencing is correlated with tumor progression, suggesting that it might be associated with the acquisition of a metastatic phenotype. ADAM23 exerts its function mainly through the disintegrin domain, because its metalloprotease domain is inactive. Analysis of ADAM23 binding to integrins has revealed a specific interaction with α_vβ₃ integrin mediated by the disintegrin domain. Altered expression of α_vβ₃ integrin has been observed in different types of tumors, and expression of this integrin in the activated form has been shown to promote metastasis formation. Here, we investigated the possibility that interaction between ADAM23 and α_vβ₃ integrin might negatively modulate α_vβ₃ activation during metastatic progression. ADAM23 expression was knocked down using short hairpin RNA in the MDA-MB-435 cell line, which has been extensively used as a model for α_vβ₃ integrin activation. Ablation of ADAM23 enhanced α_vβ₃ integrin activation by at least 2- to 4-fold and ADAM23 knockdown cells showed enhanced migration and adhesion to classic α_vβ₃ integrin ligands. Ablation of ADAM23 expression also enhanced pulmonary tumor cell arrest in immunodeficient mice. To complement our findings with clinical evidence, we showed that silencing of ADAM23 gene by DNA promoter hypermethylation in a collection of 94 primary breast tumors was significantly associated with lower distant metastases–free and disease-specific survivals and was an independent prognostic factor for poor disease outcome. Our results strongly support a functional role of ADAM23 during metastatic progression by negatively modulating α_vβ₃ integrin activation. [Cancer Res 2009;69(13):5546–52]