G1P3-induced mtROS Augments Caveolae Mediated Internalization of Tight Junction Protein Claudin-1 to Promote Breast Cancer Cell Metastasis
Abstract: Elevated expression of G1P3 (IFI6), a mitochondrial localized antiapoptotic protein, is associated with poor overall and distant metastasis free survival in breast cancer patients. Subsequent studies from our group reported its role in mitochondrial reactive oxygen species (mtROS) induction to promote breast cancer metastasis. However, it is unclear exactly how G1P3 induces cancer cell metastasis. Network analysis of differentially expressed genes in G1P3 expressing cells (MCF-7G1P3) identified upregulation of caveolin and vesicle mediated endocytic pathways in MCF-7G1P3 cells. We and others identified attenuation of adherence and tight junctions in G1P3 expressing cells. The formation of robust cell-cell interactions are known to antagonize cell migration. Therefore, we hypothesized that G1P3-induced mtROS promote cancer cell metastasis by augmenting caveolae mediated internalization of tight junction protein claudin-1. To test the hypothesis, formation of tight junctions in MCF-7Vector and MCF-7G1P3 cells were assessed by measuring resistance across cell layer using a Millicell ERS volt-ohm meter. Relative to MCF-7Vector, resistance in MCF-7G1P3 cells were significantly less on days 1 (0.524 fold), 2 (0.529 fold), and 3 (0.552 fold) (p ≤ 0.05). Moreover, Caveolin-1, a major mediator of endocytosis was upregulated in MCF-7G1P3 cells in both quantitative RT-PCR (3.0 fold) and in immunofluorescence analyses (p ≤ 0.05). Mito-TEMPO, a mitochondrial ROS scavenger, suppressed Caveolin-1 expression MCF-7G1P3 cells and restored resistance across membrane suggesting restoration of tight junctions in G1P3 expressing cells. In summary, our results suggest a novel mechanism of G1P3 induced metastasis by augmented caveolae mediated internalization of tight junctions to attenuate cell-cell interactions. Interrupting G1P3-induced internalization of Claudin-1 may prevent metastasis to improve clinical outcomes in breast cancer patients.
Naimishaba Parmar*, Anne Davenport, Judith M. Ball, and Venu Cheriyath, PhD
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