High Motility of Triple-negative Breast Cancer Cells Is Due to Repression of Plakoglobin Gene by Metastasis Modulator Protein SLUG
ABSTRACT One of highly pathogenic breast cancer cell types are the triple negative (negative in the expression of estrogen, progesterone, and ERBB2 receptors) breast cancer cells. These cells are highly motile and metastatic and are characterized by high levels of the metastasis regulator protein SLUG. Using isogenic breast cancer cell systems we have shown here that high motility of these cells is directly correlated with the levels of the SLUG in these cells. Because epithelial/mesenchymal cell motility is known to be negatively regulated by the catenin protein plakoglobin, we postulated that the transcriptional repressor protein SLUG increases the motility of the aggressive breast cancer cells through the knockdown of the transcription of the plakoglobin gene. We found that SLUG inhibits the expression of plakoglobin gene directly in these cells. Overexpression of SLUG in the SLUG-deficient cancer cells significantly decreased the levels of mRNA and protein of plakoglobin. On the contrary, knockdown of SLUG in SLUG-high cancer cells elevated the levels of plakoglobin. Blocking of SLUG function with a double-stranded DNA decoy that competes with the E2-box binding of SLUG also increased the levels of plakoglobin mRNA, protein, and promoter activity in the SLUG-high triple negative breast cancer cells. Overexpression of SLUG in the SLUG-deficient cells elevated the motility of these cells. Knockdown of plakoglobin in these low motility non-invasive breast cancer cells rearranged the actin filaments and increased the motility of these cells. Forced expression of plakoglobin in SLUG-high cells had the reverse effects on cellular motility. This study thus implicates SLUG-induced repression of plakoglobin as a motility determinant in highly disseminating breast cancer.
- SourceAvailable from: Kazuto Nishio[Show abstract] [Hide abstract]
ABSTRACT: Transcription factor Slug/SNAI2 (snail homolog 2) plays a key role in the induction of the epithelial mesenchymal transition in cancer cells; however, whether the overexpression of Slug mediates the malignant phenotype and alters drug sensitivity in lung cancer cells remains largely unclear. We investigated Slug focusing on its biological function and involvement in drug sensitivity in lung cancer cells. Stable Slug transfectants showed typical morphological changes compared with control cells. Slug overexpression did not change the cellular proliferations; however, migration activity and anchorage-independent growth activity with an antiapoptotic effect were increased. Interestingly, stable Slug overexpression increased drug sensitivity to tubulin-binding agents including vinorelbine, vincristine, and paclitaxel (5.8- to 8.9-fold increase) in several lung cancer cell lines but did not increase sensitivity to agents other than tubulin-binding agents. Real-time RT-PCR (polymerase chain reaction) and western blotting revealed that Slug overexpression downregulated the expression of βIII and βIVa-tubulin, which is considered to be a major factor determining sensitivity to tubulin-binding agents. A luciferase reporter assay confirmed that Slug suppressed the promoter activity of βIVa-tubulin at a transcriptional level. Slug overexpression enhanced tumor growth, whereas Slug overexpression increased drug sensitivity to vinorelbine with the downregulation of βIII and βIV-tubulin in vivo. Immunohistochemistry of Slug with clinical lung cancer samples showed that Slug overexpression tended to be involved in response to tubulin-binding agents. In conclusion, our data indicate that Slug mediates an aggressive phenotype including enhanced migration activity, anoikis suppression, and tumor growth, but increases sensitivity to tubulin-binding agents via the downregulation of βIII and βIVa-tubulin in lung cancer cells.Cancer Medicine 04/2013; 2(2):144-54. DOI:10.1002/cam4.68
- [Show abstract] [Hide abstract]
ABSTRACT: Plakoglobin (γ-catenin), a constituent of the adherens junction and desmosomes, has signaling capabilities typically associated with tumor/metastasis suppression through mechanisms that remain undefined. To determine the role of plakoglobin during tumorigenesis and metastasis, we expressed plakoglobin in human tongue squamous cell carcinoma (SCC9) cells and compared the mRNA profiles of parental SCC9 cells and their plakoglobin-expressing transfectants (SCC9-PG). We detected several p53-target genes whose levels were altered upon plakoglobin expression. In this study, we identified the p53 regulated tumor suppressor 14-3-3σ as a direct plakoglobin-p53 target gene. Coimmunoprecipitation experiments revealed that plakoglobin and p53 interact while chromatin immunoprecipitation and electrophoretic mobility shift assays revealed that plakoglobin and p53 associate with the 14-3-3σ promoter. Furthermore, luciferase reporter assays showed that p53 transcriptional activity is increased in the presence of plakoglobin. Finally, knockdown of plakoglobin in MCF-7 cells followed by luciferase assays confirmed that p53 transcriptional activity is enhanced in the presence of plakoglobin. Our data suggest that plakoglobin regulates gene expression in conjunction with p53 and that plakoglobin may regulate p53 transcriptional activity, which may account, in part, for the tumor/metastasis suppressor activity of plakoglobin.Journal of Cell Science 05/2013; 126(14). DOI:10.1242/jcs.120642 · 5.33 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: Plakoglobin (γ-catenin) is a homolog of β-catenin with dual adhesive and signaling functions. Plakoglobin participates in cell-cell adhesion as a component of the adherens junction and desmosomes whereas its signaling function is mediated by its interactions with various intracellular protein partners. To determine the role of plakoglobin during tumorigenesis and metastasis, we expressed plakoglobin in the human tongue squamous cell carcinoma (SCC9) cells and compared the mRNA profiles of parental SCC9 cells and their plakoglobin-expressing transfectants (SCC9-PG). We observed that the mRNA levels of SATB1, the oncogenic chromatin remodeling factor, were decreased approximately 3-fold in SCC9-PG cells compared to parental SCC9 cells. Here, we showed that plakoglobin decreased levels of SATB1 mRNA and protein in SCC9-PG cells and that plakoglobin and p53 associated with the SATB1 promoter. Plakoglobin expression also resulted in decreased SATB1 promoter activity. These results were confirmed following plakoglobin expression in the very low plakoglobin expressing and invasive mammary carcinoma cell line MDA-MB-231 cells (MDA-231-PG). In addition, knockdown of endogenous plakoglobin in the non-invasive mammary carcinoma MCF-7 cells (MCF-7-shPG) resulted in increased SATB1 mRNA and protein. Plakoglobin expression also resulted in increased mRNA and protein levels of the metastasis suppressor Nm23-H1, a SATB1 target gene. Furthermore, the levels of various SATB1 target genes involved in tumorigenesis and metastasis were altered in MCF-7-shPG cells relative to parental MCF-7 cells. Finally, plakoglobin expression resulted in decreased in vitro proliferation, migration and invasion in different carcinoma cell lines. Together with the results of our previous studies, the data suggests that plakoglobin suppresses tumorigenesis and metastasis through the regulation of genes involved in these processes.PLoS ONE 11/2013; 8(11):e78388. DOI:10.1371/journal.pone.0078388 · 3.53 Impact Factor