Epithelial to mesenchymal transition (EMT) is a process during which cells lose their epithelial characteristics, for instance cell polarity and cell–cell contact, and gain mesenchymal properties, such as increased motility. In colorectal cancer (CRC), EMT is associated with an invasive or metastatic phenotype. In this review, we discuss recent studies exploring novel regulation mechanisms of EMT in CRC, including the identification of new CRC EMT regulators. Upregulation of inducers can promote EMT, leading to increased invasiveness and metastasis in CRC. These inducers can downregulate E-cadherin and upregulate N-cadherin and vimentin (VIM) through modulating EMT-related signaling pathways, for instance WNT/β-catenin and TGF-β, and EMT transcription factors, such as zinc finger E-box binding homeobox 1 (ZEB1) and ZEB2. In addition, several microRNAs (miRNAs), including members of the miR-34 and miR-200 families, are found to target mRNAs of EMT-transcription factors, for example ZEB1, ZEB2, or SNAIL. Downregulation of these miRNAs is associated with distant metastasis and advanced stage tumors. Furthermore, the role of EMT in circulating tumor cells (CTCs) is also discussed. Mesenchymal markers on the surface of EMT CTCs were found to be associated with metastasis and could serve as potential biomarkers for metastasis. Altogether, these studies indicate that EMT is orchestrated by a complicated network, involving regulators of different signaling pathways. Further studies are required to understand the mechanisms underlying EMT in CRC.

Higher frequency of Smad4 inactivation or loss of expression is observed in metastasis of colorectal cancer (CRC) leading to unfavourable survival and contributes to chemoresistance. However, the molecular mechanism of how Smad4 regulates chemosensitivity of CRC is unknown. We evaluated how the loss of Smad4 in CRC enhanced chemoresistance to 5-fluorouracil (5-FU) using two CRC cell lines in vitro and in vivo. Immunoblotting with cell and tumour lysates and immunohistochemical analyses with tissue microarray were performed. Knockdown or loss of Smad4 induced tumorigenicity, migration, invasion, angiogenesis, metastasis, and 5-FU resistance. Smad4 expression in mouse tumours regulated cell-cycle regulatory proteins leading to Rb phosphorylation. Loss of Smad4 activated Akt pathway that resulted in upregulation of anti-apoptotic proteins, Bcl-2 and Bcl-w, and Survivin. Suppression of phosphatidylinositol-3-kinase (PI3K)/Akt pathway by LY294002 restored chemosensitivity of Smad4-deficient cells to 5-FU. Vascular endothelial growth factor-induced angiogenesis in Smad4-deficient cells might also lead to chemoresistance. Low levels of Smad4 expression in CRC tissues correlated with higher levels of Bcl-2 and Bcl-w and with poor overall survival as observed in immunohistochemical staining of tissue microarrays. Loss of Smad4 in CRC patients induces resistance to 5-FU-based therapy through activation of Akt pathway and inhibitors of this pathway may sensitise these patients to 5-FU.

Epithelial to mesenchymal transition (EMT) is a process that allows an epithelial cell to acquire a mesenchymal phenotype through multiple biochemical changes resulting in an increased migratory capacity. During cancer progression, EMT is found to be associated with an invasive or metastatic phenotype. In this review, we focus on the discussion of recent studies about the regulation of EMT by cigarette smoking. Various groups of active compounds found in cigarette smoke such as polycyclic aromatic hydrocarbons (PAH), nicotine-derived nitrosamine ketone (NNK), and reactive oxygen specicies (ROS) can induce EMT through different signaling pathways. The links between EMT and biological responses to cigarette smoke, such as hypoxia, inflammation, and oxidative damages, are also discussed. The effect of cigarette smoke on EMT is not only limited to cancer types directly related to smoking, such as lung cancer, but has also been found in other types of cancer. Altogether, this review emphasizes the importance of understanding molecular mechanisms of the induction of EMT by cigarette smoking and will help in identifying novel small molecules for targeting EMT induced by smoking.

NOTCH signaling exerts essential roles in normal and malignant intestinal physiology and the homeostasis of cancer stem-like cells (CSC), but the basis for this latter role remains obscure. The signaling scaffold protein STRAP is upregulated in several cancers, where it promotes tumorigenicity and metastasis. Here we report a novel oncogenic function for STRAP in maintaining CSC subpopulations in a heterogeneous mixture by antagonizing formation of the chromatin modifier PRC2 and by epigenetically activating NOTCH signals in human colorectal cancer. Silencing STRAP sensitized colorectal cancer cells to chemotherapeutic drugs in vitro and in vivo. STRAP depletion also contributed to a reduced stem-like phenotype of colorectal cancer cells, as indicated by reduced expression of the CSC signature and NOTCH signaling regulators in vitro and by diminished tumorigenesis in vivo. Genes encoding some upstream activators of NOTCH were highly enriched for H3K27me3, which forms repressive chromatin domains upon STRAP silencing. Mechanistically, STRAP competitively disrupted association of the PRC2 subunits EZH2 and SUZ12, thereby inhibiting PRC2 assembly. Restoring the NOTCH pathway by lentiviral expression of NICD1 or HES1 in STRAP-depleted tumor cells reversed the CSC phenotype. In 90 colorectal cancer clinical specimens, a significant positive correlation was documented between the expression of STRAP and HES1. Overall, our findings illuminated a novel STRAP–NOTCH1–HES1 molecular axis as a CSC regulator in colorectal cancer, with potential implications to improve treatment of this disease. Cancer Res; 77(20); 5464–78. ©2017 AACR.

Epidemiologic studies have shown that most cases of lung cancers (85%–90%) are directly attributable to cigarette smoking. Although much information has been gained about the effects of cigarette smoking on various signaling pathways causing lung cancer, nothing is known about the effect of cigarette smoking on the TGF-β–induced tumor suppressor function in lung cancer. To address this issue, lung adenocarcinoma A549 and immortalized bronchial epithelial HPL1A cells were chronically treated with cigarette smoke condensate (CSC) and dimethyl sulfoxide (as a control) to mimic the conditions of long-term cigarette smoking. Prolonged exposure of these cells to CSC resulted in a decrease in Smad3 and Smad4 complex formation and TGF-β–mediated transcription due to reduced expression of Smad3. Long-term CSC treatment reduced apoptosis, increased cell viability, decreased TGF-β–mediated growth inhibition, and enhanced tumorigenicity. The decrease in apoptosis is due to the upregulation of Bcl-2, which is a downstream target of Smad3. Re-expression of Smad3 in the CSC-treated cells restored TGF-β signaling, increased apoptosis, and decreased cell viability and tumorigenicity. Withdrawal of CSC treatment resulted in the restoration of Smad3 expression, reduction in cell viability, and increased TGF-β–mediated growth inhibition. Expression of Smad3 is lower in lung tumors of current smokers than that observed in never-smokers. Collectively, these data provide evidence that cigarette smoking promotes tumorigenicity partly by abrogating TGF-β–mediated growth inhibition and apoptosis by reducing expression of Smad3. Cancer Prev Res; 5(3); 453–63. ©2012 AACR.

Transforming growth factor β (TGF-β)/Smad signaling is involved in colorectal carcinoma (CRC) development and progression. The frequent loss of SMAD4 is associated with liver metastasis and poor prognosis of CRC, but the underlying mechanism remains elusive. This study aimed to elucidate the role of Smad-independent TGF-β signaling in CRC metastasis. Immunohistochemistry showed that Smad4 level was negatively correlated with TNM stage and phospho-ERK level in human CRCs and liver metastasis samples. Knockdown of Smad4 in CT26 and HCT116 cells activated ERK pathway, altered the expression of MMP2 and COX-2, promoted cell motility, migration, and invasion in vitro, enhanced metastasis, and shortened the survival of metastatic tumor-bearing mice. MEK inhibitor U0126 and GSK1120212 inhibited the motility, migration, and invasion of Smad4 knockdown cells, inhibited metastasis, and prolonged the survival of metastatic tumor-bearing mice. Furthermore, MEK inhibitor could reverse the changes of phospho-ERK, MMP2, and COX-2 levels. In conclusion, our results indicate that ERK pathway plays a key oncogenic role in CRC with SMAD4 inactivation mutations, and implicate ERK as a potential therapeutic target for CRC liver metastasis.