SIX4 promotes metastasis through STAT3 activation in breast cancer.

Sine oculis homeobox homolog 4 (SIX4), a member of the SIX family, play important role in the development and construction of vertebrate tissues and organs. There is very little known about the function of SIX4 in cancer cells. Herein, we investigated whether SIX4 promote cancer metastasis in addition to its direct role in breast cancer cells. Our study showed that the expression of SIX4 was profoundly increased in breast cancer tissues, and the high expression of SIX4 correlated strongly with distant metastasis and poor prognosis. Functional experiments demonstrated that SIX4 obviously promoted the cell migration and invasion of breast cancer cells, and up-regulated the expression of EMT mesenchymal marker, down-regulated the epithelial molecules by Snail induction in vitro. Moreover, SIX4 knockdown significant suppressed breast cancer lung metastasis in vivo. Mechanistically, SIX4 directly interacted with STAT3 and promoted the phosphorylated STAT3 nuclear translocation, thereby inducing EMT program activation. Collectively, our findings demonstrated that SIX4 may be a promising target for intervention to prevent cancer metastasis.