Notch signaling induces EMT in OSCC cell lines in a hypoxic environment

Abstract

Epithelial-mesenchymal transition (EMT) is an early step in the acquisition of invasiveness by malignant tumors. It has been clarified that the tumor microenvironment affects malignancy in a number of different carcinomas, in particular, that a hypoxic environment induces EMT. Activation of Notch signaling induces EMT, but it remains unclear how the Notch pathway is involved in oral squamous cell carcinoma (OSCC) under hypoxia. Three OSCC cell lines were cultured for examination under hypoxic (1% O2) and normoxic (21% O2) conditions. Expression of E-cadherin was investigated as a hallmark of EMT by immunohistochemical examination. Cell motility and invasion were examined by wound-healing and invasion assays, respectively. The expression of Notch pathway molecules was analyzed by qPCR. Hypoxia increased the mRNA expression of Notch receptors, ligands and target genes, and Snail. Hypoxia decreased the expression of E-cadherin, and increased the motility and invasiveness of OSCC cell lines. γ-secretase inhibitor, a Notch-specific inhibitor, prevented these effects caused by h-ypoxia. These findings suggest that hypoxia induces EMT in OSCC cell lines via activation of Notch signaling, and inhibition of the Notch signaling pathway to suppress EMT may be a useful approach for the treatment of OSCC.

Mechanisms of Invasion in Head and Neck Cancer

“…Notch signaling can induce EMT under hypoxic conditions, with increased expression of Notch pathway molecules and Snail, decreased expression of E-cadherin, and an increase in invasiveness. 77 In addition to inducing EMT and increased invasiveness, Snail has also been shown to induce stem-like properties in OSCC. 224 Adhesion-related signaling molecules that are important for EMT and invasion include ILK 149 and FAK.…”

“…[71][72][73][74][75][76] Invasion is stimulated by hypoxia in a Notch-dependent fashion. 77 Inhibition of Notch can also suppress MMP production. 78 85,86 or through phosphorylation of ezrin 87 and yes-associated protein.…”

“…40 Hypoxia in the tumor microenvironment can induce Notch and EMT factors, such as Slug and Snail, to increase invasion. 77,274 In addition, MMP-9 can be induced by hypoxia to enhance invasion in a Na…”

Stem Cells in Pancreatic Cancer

“…Snail and Slug) in tumor samples [42]. Moreover, the expression of EMT-specific genes has been identified at the level of the invasive front of primary tumors [32] and reversely, the expression of CSCs markers can be induced by overexpressing Snail or Twist, the most important transcription factors involved in the EMT process [43]. From the other point of view, cancer cells from metastasis after the EMT process can show a CSC phenotype and TGF-β signaling is considered to be a crucial factor involved in these processes [44].…”

“…Notch signaling is responsible for cell fate, proliferation, differentiation, apoptosis and the maintenance of stem cells and also for hypoxia, which can activate EMT in cancer [32]. It is also considered that Notch can regulate endothelial and mesenchymal markers to sustain mesenchymal transformation [33].…”