The Six1 homeoprotein induces human mammary carcinoma cells to undergo epithelial-mesenchymal transition and metastasis in mice through increasing TGF-β signaling
Douglas S. Micalizzi, … , William P. Schiemann, Heide L. Ford
Douglas S. Micalizzi, … , William P. Schiemann, Heide L. Ford
Published August 24, 2009
Citation Information: J Clin Invest. 2009;119(9):2678-2690. https://doi.org/10.1172/JCI37815.
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Research Article

The Six1 homeoprotein induces human mammary carcinoma cells to undergo epithelial-mesenchymal transition and metastasis in mice through increasing TGF-β signaling

Abstract

Inappropriate activation of developmental pathways is a well-recognized tumor-promoting mechanism. Here we show that overexpression of the homeoprotein Six1, normally a developmentally restricted transcriptional regulator, increases TGF-β signaling in human breast cancer cells and induces an epithelial-mesenchymal transition (EMT) that is in part dependent on its ability to increase TGF-β signaling. TGF-β signaling and EMT have been implicated in metastatic dissemination of carcinoma. Accordingly, we used spontaneous and experimental metastasis mouse models to demonstrate that Six1 overexpression promotes breast cancer metastasis. In addition, we show that, like its induction of EMT, Six1-induced experimental metastasis is dependent on its ability to activate TGF-β signaling. Importantly, in human breast cancers Six1 correlated with nuclear Smad3 and thus increased TGF-β signaling. Further, breast cancer patients whose tumors overexpressed Six1 had a shortened time to relapse and metastasis and an overall decrease in survival. Finally, we show that the effects of Six1 on tumor progression likely extend beyond breast cancer, since its overexpression correlated with adverse outcomes in numerous other cancers including brain, cervical, prostate, colon, kidney, and liver. Our findings indicate that Six1, acting through TGF-β signaling and EMT, is a powerful and global promoter of cancer metastasis.

Authors

Douglas S. Micalizzi, Kimberly L. Christensen, Paul Jedlicka, Ricardo D. Coletta, Anna E. Barón, J. Chuck Harrell, Kathryn B. Horwitz, Dean Billheimer, Karen A. Heichman, Alana L. Welm, William P. Schiemann, Heide L. Ford

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Figure 5

Increased TGF-β signaling is necessary for elements of Six1-induced EMT.

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Increased TGF-β signaling is necessary for elements of Six1-induced EMT....
(A) TβRIIDN inhibited TGF-β signaling, as assessed by the TGF-β–responsive promoter 3TP after normalizing to renilla luciferase. (B and C) Inhibition of TGF-β signaling with TβRIIDN reversed E-cadherin and β-catenin relocalization as assessed by fractionation. Graphs represent quantification of Western blots for the ratio of E-cadherin or β-catenin in the soluble versus the insoluble fractions. Data are presented as mean value ± SEM in at least 3 independent experiments. (D) Inhibition of TGF-β signaling with TβRIIDN reverses β-catenin–dependent transcription, as assessed by a β-catenin–responsive reporter (TOP-flash) after normalizing to renilla luciferase. Data are presented as mean value ± SD. P values represent statistical analysis using a paired t test.