Previous studies mainly focused on the function of STMN1 in several cancers, including hepatocellular, gastric, colon, pancreatic and lung cancer [23–27]. However, STMN2, as a novel discovered oncogene, is poorly understood in cancer, especially in PC. In current study, we first identified STMN2 as a novel target of β-catenin/TCF-mediated transcription in PC cells. Overexpression of STMN2 contributes to the aggressive clinical stage of PC patients in coordination with WNT/β-catenin signaling. Meanwhile, STMN2 promotes cell proliferation and EMT in PC via activating WNT/β-catenin mediated EMT and Cyclin D1 signaling, which has not been studied yet.
We first found that STMN2 was overexpressed in PC patients, which was positively associated with tumor size, T stage, lymph node metastasis and the poor survival of PC patients. STMN2 was also overexpressed in hepatocellular, neuroblastoma and ovarian cancer [11–13]. STMN2 overexpression was associated with advanced clinical characters and bad prognosis in hepatocellular cancer . Meanwhile, it was an independent unfavorable prognostic factor in ovarian cancer . Thus, STMN2 act as a potential oncogene based on previous and current studies. Interestingly, the combination of high SMTN2 and cytoplasmic/nuclear expression of β-catenin contributed to the much worse survival of PC patients. Meanwhile, the parallel expression of STMN2 and β-catenin were observed in both PC tissue and cell lines. It is well known that WNT/β-catenin signaling pathway closely correlates with the characteristic of EMT and potency of proliferation in cancer development [15, 28], which drive us to investigate the cooperative interaction of STMN2 and WNT/β-catenin signaling in regulating EMT and cell proliferation of PC.
In current study, STMN2 overexpression promoted EMT and cell proliferation in PC cells. EMT-like cell morphology, cell mobility and proliferation were significantly enhanced in STMN2 overexpression PC cells. However, the specific inhibitor (XAV939) of WNT/β-catenin signaling reversed STMN2 overexpression- induced function in vitro. Conversely, the specific activator (KY19382) of WNT/β-catenin signaling reversed STMN2 silencing- inhibited EMT and cell proliferation. Only one study reports the function of STMN2 in the malignant behavior of cancer that STMN2 promotes cell migration, invasion and metastasis in vitro and in hepatocellular cancer by triggers EMT . Taken together, STMN2, act as an oncogene, promotes the development of cancers partially by triggers EMT.
Further potential mechanism showed that STMN2 overexpression upregulated Snail1, Vimentin, Cyclin D1 and downregulated E-cad in vitro. XAV939 not only inhibited STMN2 expression, but also reversed STMN2 overexpression- induced EMT and Cyclin D1 signaling. Conversely, KY19382 reversed STMN2 silencing- induced EMT and Cyclin D1 signaling in vitro. Snail1, as a critical EMT stimulator, induced EMT by repressing E-cadherin and claudins with concomitant upregulation of Vimentin . Thus, STMN2 induced EMT by regulating Snail1. It is well known that Cyclin D1 plays a critical role in regulating proliferation, involving the extracellular signaling environment to cell cycle progression . High Cyclin D1 expression drives unchecked cellular proliferation promoting tumor growth . Therefore, STMN2 promoted cell proliferation by activating Cyclin D1 signaling. STMN2 also mediates nuclear translocation of Smad2/3 and enhances TGFβ signaling by destabilizing microtubules to promote EMT in hepatocellular cancer .
Previous study showed that STMN2 was a novel target of β-catenin/TCF-mediated transcription in human hepatoma cells [16, 17]. Similarly, the oncogenic function of STMN2 in PC was mediated by WNT/β-catenin signaling in current study. Activating β-catenin and STMN2 showed co-localization in the cytoplasm and nuclear in BxPC-3 cells. ChIP assays further showed that TCF binding site at -1816 to -1822 is crucial for the regulation of STMN2 expression by β-catenin/TCF. Taken together, overexpression of STMN2 promotes cell proliferation and EMT in PC mediated by WNT/β-catenin signaling.
Finally, STMN2 overexpression promoted subcutaneous tumors formation in vivo with the overexpression of EMT and Cyclin D1 signaling, which was consistent with the results in vitro.