Epithelial to mesenchymal transition (EMT) contributes to tumor progression, cancer cell invasion, and therapy resistance. EMT is regulated by transcription factors such as the protein products of the SNAI gene family, which inhibits the expression of epithelial genes. Several signaling pathways, such as TGF-beta1, IL-6, Akt, and Erk1/2, trigger EMT responses. Besides regulatory transcription factors, RNA molecules without protein translation, micro RNAs, and long non-coding RNAs also assist in the initialization of the EMT gene cluster. A challenging novel aspect of EMT research is the investigation of the interplay between tumor microenvironments and EMT. Several microenvironmental factors, including fibroblasts and myofibroblasts, as well as inflammatory, immune, and endothelial cells, induce EMT in tumor cells. EMT tumor cells change their adverse microenvironment into a tumor friendly neighborhood, loaded with stromal regulatory T cells, exhausted CD8+ T cells, and M2 (protumor) macrophages. Several EMT inhibitory mechanisms are instrumental in reversing EMT or targeting EMT cells. Currently, these mechanisms are also significant for clinical use.

Background: Epithelial to mesenchymal transition (EMT) promotes therapy resistance in head and neck cancer (HNC) cells. In this study, EMT was quantified in HNC tumor samples by the cellular co-localization of cytokeratin/vimentin, E-cadherin/β-catenin and by Slug expression. Methods: Tissue samples from HNC patients were stained with antibody pairs against cytokeratin/vimentin and E-cadherin/β-catenin. Epithelial–mesenchymal co-localization was quantified using immunofluorescence multichannel image cytometry. Double positivity was confirmed using confocal microscopy. Slug was semi-quantified by 2 specialists and quantified by bright field image cytometry. Results: Tumor samples of 102 patients were investigated. A loss of E-cadherin positive cells (56.9 ± 2.6% vs. 97.9 ± 1.0%; p < 0.0001) and E-cadherin/β-catenin double positive cells (15.4 ± 5.7% vs. 85.4 ± 1.2%; p < 0.0001) was observed in tumor samples. The percentage of Slug positive cells was increased in tumor samples (12.1 ± 3.6% vs. 3.2 ± 2.6%; p = 0.001). Ordinal Slug scores judged by two specialists closely correlated with percentage of Slug-positive cells (Spearman’s rho = 0.81; p < 0.001). Slug score correlated negatively with the percentage of E-cadherin positive cells (r = 0.4; p = 0.006), the percentage of E-cadherin/β-catenin positive cells (r = 0.5; p = 0.001) and positively with cytokeratin/vimentin positive cells (r = 0.4, p = 0.003). Conclusion: EMT can be assessed in HNC tumor probes by cytokeratin/vimentin co-expression and loss of E-cadherin/β-catenin co-expression. Slug score provides a convenient surrogate marker for EMT.

Epithelial to mesenchymal transition (EMT) is clinically relevant in head and neck squamous cell carcinoma (HNSCC). We hypothesized that EMT-transcription factors (EMT-TFs) and an anti-EMT factor, Krüppel-like-factor-4 (KLF4) regulate EMT in HNSCC. Ten control mucosa and 37 HNSCC tissue samples and three HNSCC cell lines were included for investigation of EMT-TFs, KLF4 and vimentin at mRNA and protein levels. Slug gene expression was significantly higher, whereas, KLF4 gene expression was significantly lower in HNSCC than in normal mucosa. In the majority of HNSCC samples, there was a significant negative correlation between KLF4 and Slug gene expression. Slug gene expression was significantly higher in human papilloma virus (HPV) negative HNSCC, and in tumor samples with irregular p53 gene sequence. Transforming-growth-factor-beta-1 (TGF- β1) contributed to downregulation of KLF4 and upregulation of Slug. Two possible regulatory pathways could be suggested: (1) EMT-factors induced pathway, where TGF-β1 induced Slug together with vimentin, and KLF4 was down regulated at the same time; (2) p53 mutations contributed to upregulation and stabilization of Slug, where also KLF4 could co-exist with EMT-TFs.