Epithelial-Mesenchymal Transition in tumor microenvironment

Metformin: an emerging new therapeutic option for targeting cancer stem cells and metastasis

Metastasis is an intricate process by which a small number of cancer cells from the primary tumor site undergo numerous alterations, which enables them to form secondary tumors at another and often multiple sites in the host. Transition of a cancer cell from epithelial to mesenchymal phenotype is thought to be the first step in the progression of metastasis. Recently, the recognition of cancer stem cells has added to the perplexity in understanding metastasis, as studies suggest cancer stem cells to be the originators of metastasis. All current and investigative drugs have been unable to prevent or reverse metastasis, as a result of which most metastatic cancers are incurable. A potential drug that can be considered is metformin, an oral hypoglycemic drug. In this review we discuss the potential of metformin in targeting both epithelial to mesenchymal transition and cancer stem cells in combating cancer metastases.

Silencing Wnt2B by siRNA interference inhibits metastasis and enhances chemotherapy sensitivity in ovarian cancer

OBJECTIVE

Wnt2B overexpression is thought to be involved in tumor progression through the activation of the canonical Wingless and INT-1 signaling pathway. However, the mechanism of Wnt2B signaling in oncogenesis is unknown. In this study, we investigated whether silencing Wnt2B expression could inhibit the invasiveness of ovarian cancer cells and reduce drug resistance.

METHODS/MATERIALS

Four ovarian carcinoma cell lines, SKOV3, OV2008, A2780, and C13K, were used. Protein levels were studied by Western blotting. The colony formation ability and invasive ability were determined through colony formation assay and the Matrigel transwell assay, respectively. Cell viability was determined by the 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide assay, whereas apoptosis was assessed using flow cytometry analysis.

RESULTS

Among the 4 ovarian carcinoma cell lines, the A2780 cells and C13K cells expressed Wnt2B, and these 2 cell lines were used for analyzing the mechanism of Wnt2B. The down-regulation of Wnt2B inhibited cell colony formation and invasiveness. Enhanced paclitaxel or cisplatin sensitivity was observed in A2780 cells or C13K cells treated with Wnt2B siRNA, respectively. In the presence of Wnt2B siRNA treatment, the caspase-9/B-cell lymphoma 2 (BCL2)/B-cell lymphoma-xL (BCL-xL) pathway and the epithelial-mesenchymal transition/phosphorylated protein kinase B pathway were inhibited.

CONCLUSION

These data suggest that Wnt2B indeed plays an important role in ovarian cancer metastasis and drug resistance. This study may provide a new therapeutic target for and a better understanding of ovarian cancer therapy.

Epithelial to mesenchymal transition in cutaneous squamous cell carcinoma is correlated with COX-2 expression but not with the presence of stromal macrophages or CD10-expressing cells

Epithelial to mesenchymal transition (EMT) is an intricate process by which epithelial cells loose epithelial characteristics and acquire a mesenchymal-like phenotype. EMT and cyclooxygenase 2 (COX-2) expression are related to tumor invasion and metastasis. The tumor microenvironment plays a major role in tumor progression and the induction of EMT. Here, we investigated the relationship between EMT and COX-2 expression as well as tumor-associated macrophages (TAM) and CD10-positive stromal cells during the development of cutaneous squamous neoplastic lesion. We performed immunohistochemical staining for vimentin, E-cadherin, β-catenin, COX-2, CD68, and CD10 in 41 cases of squamous cell cancers (SCC), 20 of Bowen's disease, 30 of actinic keratosis, and 30 samples of normal skin. SCC cells showed significantly increased vimentin expression and reduced expression of membranous E-cadherin and β-catenin compared with cells in precursor lesions and in normal skin. COX-2 expression was also markedly increased in SCC cells. E-cadherin expression was positively correlated with β-catenin expression and inversely correlated with COX-2 expression in SCC cells. The number of TAM and CD10-positive stromal cells increased from the normal skin to precursor lesions and SCC cells. The number of TAM and of CD10-positive stromal cells did not correlate with the expression of E-cadherin, β-catenin, COX-2, and vimentin in SCC cells. We suggest that cutaneous SCC cells show EMT, which appears to be correlated with COX-2 expression but not with stromal CD10 expression and TAM.

Role of the integrin-linked kinase (ILK)/Rictor complex in TGFβ-1-induced epithelial-mesenchymal transition (EMT)

Epithelial-to-mesenchymal transition (EMT) causes fibrosis, cancer progression and metastasis. Integrin-linked kinase (ILK) is a focal adhesion adaptor and a serine/threonine protein kinase that regulates cell proliferation, survival and EMT. Elucidating the molecular mechanisms necessary for development and progression of human malignancies is critical to predict the most appropriate targets for cancer therapy. Here, we used transforming growth factor beta-1 (TGFβ-1) to promote EMT and migration in mammary epithelial cells. We demonstrate a requirement of ILK activity for TGFβ-1-mediated EMT in mammary epithelial cells. In addition to nuclear translocation of Snail and Slug, TGFβ-1 treatment also induced expression of the mammalian target of rapamycin complex 2 component Rictor and its phosphorylation on Thr1135. Interestingly, TGFβ-1 treatment also induced an interaction between ILK and Rictor. All of these TGFβ-1-induced processes were significantly suppressed by inhibiting ILK activity or by disrupting the ILK/Rictor complex using small-interfering RNA-mediated knockdown. Furthermore, we identified ILK/Rictor complex formation in cancer but not in normal cell types, and this was accompanied by ILK-dependent phosphorylation of Rictor on residue Thr1135. Inhibition of ILK partially reversed the basal mesenchymal phenotype of MDA-MB-231 cells and prevented EMT in MCF10A cells after TGFβ-1 treatment. These data demonstrate a requirement for ILK function in TGFβ-1-induced EMT in mammary epithelial cells and identify the ILK/Rictor complex as a potential molecular target for preventing/reversing EMT.

Oncogenic role and therapeutic target of leptin signaling in breast cancer and cancer stem cells

Significant correlations between obesity and incidence of various cancers have been reported. Obesity, considered a mild inflammatory process, is characterized by a high level of secretion of several cytokines from adipose tissue. These molecules have disparate effects, which could be relevant to cancer development. Among the inflammatory molecules, leptin, mainly produced by adipose tissue and overexpressed with its receptor (Ob-R) in cancer cells is the most studied adipokine. Mutations of leptin or Ob-R genes associated with obesity or cancer are rarely found. However, leptin is an anti-apoptotic molecule in many cell types, and its central roles in obesity-related cancers are based on its pro-angiogenic, pro-inflammatory and mitogenic actions. Notably, these leptin actions are commonly reinforced through entangled crosstalk with multiple oncogenes, cytokines and growth factors. Leptin-induced signals comprise several pathways commonly triggered by many cytokines (i.e., canonical: JAK2/STAT; MAPK/ERK1/2 and PI-3K/AKT1 and, non-canonical signaling pathways: PKC, JNK and p38 MAP kinase). Each of these leptin-induced signals is essential to its biological effects on food intake, energy balance, adiposity, immune and endocrine systems, as well as oncogenesis. This review is mainly focused on the current knowledge of the oncogenic role of leptin in breast cancer. Additionally, leptin pro-angiogenic molecular mechanisms and its potential role in breast cancer stem cells will be reviewed. Strict biunivocal binding-affinity and activation of leptin/Ob-R complex makes it a unique molecular target for prevention and treatment of breast cancer, particularly in obesity contexts.

Oncogenic role and therapeutic target of leptin signaling in breast cancer and cancer stem cells

Significant correlations between obesity and incidence of various cancers have been reported. Obesity, considered a mild inflammatory process, is characterized by a high level of secretion of several cytokines from adipose tissue. These molecules have disparate effects, which could be relevant to cancer development. Among the inflammatory molecules, leptin, mainly produced by adipose tissue and overexpressed with its receptor (Ob-R) in cancer cells is the most studied adipokine. Mutations of leptin or Ob-R genes associated with obesity or cancer are rarely found. However, leptin is an anti-apoptotic molecule in many cell types, and its central roles in obesity-related cancers are based on its pro-angiogenic, pro-inflammatory and mitogenic actions. Notably, these leptin actions are commonly reinforced through entangled crosstalk with multiple oncogenes, cytokines and growth factors. Leptin-induced signals comprise several pathways commonly triggered by many cytokines (i.e., canonical: JAK2/STAT; MAPK/ERK1/2 and PI-3K/AKT1 and, non-canonical signaling pathways: PKC, JNK and p38 MAP kinase). Each of these leptin-induced signals is essential to its biological effects on food intake, energy balance, adiposity, immune and endocrine systems, as well as oncogenesis. This review is mainly focused on the current knowledge of the oncogenic role of leptin in breast cancer. Additionally, leptin pro-angiogenic molecular mechanisms and its potential role in breast cancer stem cells will be reviewed. Strict biunivocal binding-affinity and activation of leptin/Ob-R complex makes it a unique molecular target for prevention and treatment of breast cancer, particularly in obesity contexts.