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.