Characterization of the expression of the pro-metastatic Mena^INV isoform during breast tumor progression

Several functionally distinct isoforms of the actin regulatory Mena are produced by alternative splicing during tumor progression. Forced expression of the Mena^INV isoform drives invasion, intravasation and metastasis. However, the abundance and distribution of endogenously expressed Mena^INV within primary tumors during progression remain unknown, as most studies to date have only assessed relative mRNA levels from dissociated tumor samples. We have developed a Mena^INV isoform-specific monoclonal antibody and used it to examine Mena^INV expression patterns in mouse mammary and human breast tumors. Mena^INV expression increases during tumor progression and to examine the relationship between Mena^INV expression and markers for epithelial or mesenchymal status, stemness, stromal cell types and hypoxic regions. Further, while Mena^INV robustly expressed in vascularized areas of the tumor, it is not confined to cells adjacent to blood vessels. Altogether, these data demonstrate the specificity and utility of the anti-Mena^INV-isoform specific antibody, and provide the first description of endogenous Mena^INV protein expression in mouse and human tumors.