Abstract 297: Loss of giant obscurins expression in breast epithelium disrupts epithelial junctions and promotes cell motility and invasion.

Abstract Obscurin A (∼720kDa) and B (∼870kDa) are giant multidomain proteins, encoded by the single OBSCN gene, originally shown to play important roles in the structural organization and contractile activity of striated muscles. Early studies have indicated that the OBSCN gene is highly mutated in different types of cancers. In light of this observation, our laboratory set forth to examine the expression profile and roles of giant obscurins in normal and cancer breast tissue. Obscurins are readily expressed in breast epithelial cells, but their expression is dramatically diminished in breast cancer cells. Down-regulation of obscurin A and B using small hairpin RNAs (shRNAs) in non-tumorigenic MCF10A breast epithelial cells resulted in decreased protein expression of β-catenin and E-cadherin, which are major components of adherens junctions and have been heavily implicated in the formation and metastasis of breast tumors. Specifically, β-catenin exhibited a preferential nuclear accumulation accompanied by a concomitant loss from cell-cell junctions. Additionally, loss of obscurins led to alterations in the expression levels and localization of multiple proteins associated with epithelial to mesenchymal transition (EMT). Obscurin-deficient MCF10A cells showed significantly increased motility in 2-Dimensional (2-D) substrata and confined spaces, and invasion through a matrigel coated chamber. Consistent with this, actin filaments re-distributed to extending filopodia-like protrusions where they exhibited increased dynamics. Taken together, our findings indicate that loss of giant obscurins from breast epithelium results in disruption of cell contacts and acquisition of a mesenchymal phenotype that leads to enhanced migration and invasiveness. Citation Format: Marey Shriver, Kimberly Stroka, Konstantinos Konstantopoulos, Aikaterini Kontrogianni-Konstantopoulos. Loss of giant obscurins expression in breast epithelium disrupts epithelial junctions and promotes cell motility and invasion. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 297. doi:10.1158/1538-7445.AM2013-297