Decreased TIP30 promotes Snail-mediated epithelial–mesenchymal transition and tumor-initiating properties in hepatocellular carcinoma

The poor prognosis of hepatocellular carcinoma (HCC) is mainly due to tumor recurrence and metastases. Recently, epithelial-mesenchymal transition (EMT) has been implicated in tumor invasion and metastasis. However, the underlying molecular mechanisms are yet to be elucidated. Here, we show that 30-kDa Tat-interacting protein (TIP30), also called CC3, is significantly downregulated during transforming growth factor-β-induced EMT. In our in vitro and in vivo studies, we show that decreased TIP30 expression leads to EMT, as well as enhanced motility and invasion of HCC cells. Also, increased self-renewal ability and chemotherapeutic resistance are observed with TIP30 depletion. Moreover, Snail is one of the key transcription factors promoting EMT, and overexpression of TIP30 greatly decreased nucleic accumulation in Snail through the regulation of intracellular localization. Small interfering RNAs targeting Snail attenuated EMT and tumor-initiating properties induced by TIP30 deficiency. We further confirmed that TIP30 competitively interrupted the interaction of Snail with importin-β2 to block the nuclear import of Snail. Consistently, TIP30 expression significantly correlates with E-cadherin expression in HCC patients. TIP30 or combination of E-cadherin is a powerful marker in predicting the prognosis of HCC. Taken together, our results suggest a novel and critical role of TIP30 involved in HCC progression and aggressiveness.