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 7

Six1 increases metastatic burden in an experimental metastasis model dependent on TGF-β signaling.

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Six1 increases metastatic burden in an experimental metastasis model dep...
(A) Bioluminescent imaging of nude mice 48 days after intracardiac injection of either MCF7-Ctrl or MCF7-Six1 cells into the left ventricle. The luminescence signal is represented by the overlaid false-color image, with intensity of the signal indicated by the scale. The anesthetized mice were imaged 10 minutes after intraperitoneal injection of D-luciferin using the IVIS200 (Caliper LS). (B) Quantification of the total body luminescent signal (in photons/second) for each group at the indicated days after injection, presented as the mean ± SEM. *P < 0.05; **P < 0.01. (C) Kaplan-Meier curve representing the overall survival of the injected mice. Statistical analysis was performed using the log-rank test. (D) Quantification of luminescent signal (in photons/second) on day 48 after injection, with the cell lines indicated. Data points represent the luminescent signal of individual animals. Horizontal bars represent the median values. Statistical analysis of luminescence data from days 4–62 was performed using linear mixed models with group-by-time interaction and an unstructured variance-covariance matrix. Interaction contrasts across the 4 animal groups were obtained for each of the 5 days after injection. (E) Kaplan-Meier curve representing the overall survival of the injected mice. Statistical analysis was performed using the log-rank test.