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The cell-cell adhesion protein junctional adhesion molecule-A (JAM-A) influences epithelial cell morphology and migration. As migration is required for tumor cell invasion and metastasis, we sought to elucidate the role of JAM-A in invasive breast cancer. A breast cancer tissue microarray was analyzed for JAM-A protein expression, in parallel with analysis of JAM-A gene expression data from a breast cancer clinical dataset. Our data demonstrate a novel association between JAM-A gene and protein upregulation and poor prognosis in breast cancer. To mechanistically dissect this process, we used lentiviral technology to stably knock down JAM-A gene expression by shRNA in MCF7 breast cancer cells, which express high-endogenous levels of JAM-A. We also antagonized JAM-A function in wild-type MCF7 cells using an inhibitory antibody that blocks JAM-A dimerization. Knockdown or functional antagonism of JAM-A decreased breast cancer cell migration in scratch-wound assays. Reductions in beta1-integrin protein levels were observed after JAM-A-knockdown in MCF7 cells, suggesting a mechanism for reduced motility after loss of JAM-A. Consistent with this hypothesis, tissue microarray analysis of beta1-integrin protein expression in invasive breast cancer tissues revealed a trend toward high beta1-integrin protein levels being indicative of poor prognosis. Twenty-two percent of patients were observed to coexpress high levels of JAM-A and beta1-integrin protein, and MDA-MB-231 breast cells stably overexpressing JAM-A showed an increase in beta1-integrin protein expression. Our results are consistent with a previously unreported role for JAM-A overexpression as a possible mechanism contributing to progression in primary breast cancer; and a potential therapeutic target.
McSherry et al. (Tue,) studied this question.