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. 2015 Jul;36(1):166-72.
doi: 10.3892/ijmm.2015.2215. Epub 2015 May 19.

The ectopic expression of Snail in MDBK cells does not induce epithelial-mesenchymal transition

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The ectopic expression of Snail in MDBK cells does not induce epithelial-mesenchymal transition

Genya Izawa et al. Int J Mol Med. 2015 Jul.

Abstract

Epithelial-mesenchymal transition (EMT), a key process in the tumor metastatic cascade, is characterized by the loss of cell-cell junctions and cell polarity, as well as by the acquisition of migratory and invasive properties. However, the precise molecular events that initiate this complex EMT process are poorly understood. Snail expression induces EMT in Madin-Darby canine kidney (MDCK) cells and the human epidermoid carcinoma cell line, A431. Snail is a zinc finger transcription factor and triggers EMT by suppressing E-cadherin expression. In the present study, to broaden our knowledge of Snail‑induced EMT, we generated stable Snail transfectants using Madin-Darby bovine kidney (MDBK) cells. Contrary to the MDCK or A431 cells examined in our previous studies, the MDBK cells transfected with the Snail construct maintained an epithelial morphology and showed no sign of reduced cell-cell adhesiveness compared to the control cells. Consistent with these observations, the downregulation of epithelial marker proteins, e.g. E-cadherin and desmoglein, and the upregulation of mesenchymal marker proteins, e.g., N-cadherin and fibronectin, were not detected. Furthermore, the E-cadherin promoter was not methylated. Therefore, in the MDBK cells, the ectopic expression of Snail failed to induce EMT. As previously demonstrated, in MDCK cells, Snail expression is accompanied by the increased expression of other EMT-inducing transcription factors, e.g., Slug and zinc finger E-box-binding homeobox 1 (ZEB1). However, the MDBK cells transfected with the Snail construct did not exhibit an increased expression of these factors. Thus, it is possible that the failure to upregulate other EMT-related transcription factors may explain the lack of Snail-mediated induction of EMT in MDBK cells.

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Figures

Figure 1
Figure 1
Madin-Darby bovine kidney (MDBK) cells ectopically expressing Snail protein display characteristics of the epithelial phenotype. (A) Both the control MDBK cells transfected with an empty vector containing a neomycin resistance gene (neo) and MDBK cells transfected with an expression vector encoding HA-tagged Snail protein (Snail) displayed typical epithelial cell morphology. (B) Immunofluorescence staining with an anti-HA antibody revealed the protein expression of Snail in the nucleus, which was co-stained with DAPI. (C) Cell aggregation assays revealed that the cells ectopically expressing Snail protein had similar adhesive properties as the control (neo) cells; furthermore, the observed cell-cell adhesion was calcium-dependent, indicating that it was mediated by cadherins. Scale bars, 20 µm.
Figure 2
Figure 2
Epithelial-mesenchymal transition (EMT) is not induced in Madin-Darby bovine kidney (MDBK) cells ectopically expressing Snail. (A) Immunoblot analysis revealed that Snail expression in the MDBK cells did not decrease the expression of the epithelial markers, E-cadherin and desmoglein, and did not increase the expression of the mesenchymal markers, N-cadherin, vimentin and fibronectin. α-tubulin was used as a loading control. (B) The ectopic expression of Snail altered the splicing patterns of p120 in the Madin-Darby canine kidney (MDCK) cells, but not in the MDBK cells. (C) E-cadherin (E-cad) and N-cadherin (N-cad) were detected at the membrane of the control cells [transfected with a neomycin resistance gene (neo) cells] and in the cells ectopically expressing Snail protein (Snail). Cells were stained with the appropriate primary antibody followed by a rhodamine-labeled secondary antibody. DAPI was used to detect the nucleus. Scale bar, 20 µm.
Figure 3
Figure 3
Ectopic expression of Snail in Madin-Darby bovine kidney (MDBK) cells does not induce DNA methylation of the E-cadherin promoter. Diagram showing the position of 4 E-boxes (-403 to -398, -201 to -196, -151 to -146, and -100 to -95; red bars) and CpG dinucleotides within the E-cadherin promoter region (circles). Genomic DNA was isolated from the control cells [transfected with a neomycin resistance gene (neo) cells] and Snail cells (cells ectopically expressing Snail protein), and the methylation of the E-cadherin promoter was analyzed by bisulfite sequencing. Genomic DNA incubated with CpG methyl-transfease prior to bisulfite treatment was used as a positive control for methylated DNA. Methylated and unmethylated dinucleotides are indicated as filled and open circles, respectively.
Figure 4
Figure 4
(A) RT-PCR of Slug, Twist and ZEB1 mRNA in control cells [transfected with a neomycin resistance gene (neo) cells] and Snail cells (cells ectopically expressing Snail protein). β-actin was used as an internal control. No significant differences were observed between the control cells and the Snail cells with respect to the mRNA levels of these proteins. (B) Immunoblot analysis using anti-Slug and anti-ZEB1 antibodies. Vinculin served as a loading control. Ectopic Snail expression increased Slug and ZEB1 protein levels in Madin-Darby canine kidney (MDCK) cells, but not in Madin-Darby bovine kidney (MDBK) cells. Ectopic expression of Snail in MDBK cells slightly increased the expression level of ZEB1 protein, but the quantification of the blots using NIH ImageJ software revealed that the relative amounts of ZEB1 protein in Snail-MDBK cells were <20% of those in the Snail-MDCK cells.

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