Zhang et al. Journal of Experimental & Clinical Cancer Research 2010, 29:88 http://www.jeccr.com/content/29/1/88 Page 6 of 10 P 0.0001 0.9993 Figure 1 Representative example of the E-cadherin expression determined by immunohistochemistry. A, carcinoma cells showed strong expression (preserved pattern) in the Slug nonoverexpression case. B, carcinoma cells showed weak expression (reduced pattern) in the Slug overexpression case. (magnification, ×400). cDNA-treated FRH 0201 cells exhibited increased inva- sion (Fig. 4B; P < 0.05). Together, these data show that Slug modulates invasion of EHC cells in vitro. Discussion Recent direct evidence shows that Snail transcription factor and its family protein Slug repress E-cadherin expression in human cancer cell lines[13,22,25-30]. Down-regulation of E-cadherin causes loss of cell-to-cell adhesion. Impaired adhesion characterizes the potential of invasion and metastases, crucial steps for progression of hepatocarcinoma[3]. Thus, the down-regulation of E- cadherin promotes invasion and metastases of hepato- carcinoma and vice versa [31] . To confirm the function of Slug in EHC, we used E-cadherin-positive FRH0201 cells and slug positive QBC939 cells reported above that E-cadherin and Slug inversely express in FRH0201 and QBC939 cell lines. Our data revealed direct evidence that transient Slug expression can suppress E-cadherin protein expression and increased the motility and invision potential in QBC939 cells. Transient Slug inhibition can increase E-cadherin protein expression in FRH0201 cells, and decreased the motility and invision potential. We investigated Slug mRNA using RT-PCR and con- firmed that Slug mRNA is expressed in EHC samples. We then quantitatively analyzed the mRNA expression levels of Slug in both cancerous and noncancerous tis- sues of EHCs. We used the cancerous/noncancerous ratio of Slug mRNA to evaluate Slug expression levels in each case. 18 (34.6%) were determined to be Slug over- expression cases, and this overexpression significantly correlated with reduced E-cadherin expression. Our data show that Slug, rather than Snail, functions as a sup- presser of E-cadherin in human EHC tissue, as well as in cultured EHC cells. Recently, Paras et al. [18] reported that Slug contributed to the down-regulation of E-cadherin expression in esophageal adenocarcinoma lines. Although both proteins are produced in all verte- brate species, their functions are different among various species and different cells [32,33]. These data suggest that E-cadherin production of carcinoma cells should be regulated by the different transcriptional repressors among the different cells or tissues. Table 2 Comparison of Snail and Slug expression between preserved and reduced patterns of E-cadherin E-cadherin expression Preserved (n = 33) E-cadherin expression Reduced (n = 19) Slug mRNA Overexpression (n = 18) Nonoverexpression (n = 34) Snail mRNA Overexpression (n = 12) Nonoverexpression (n = 40) 5 (27.8) 28 (82.4) 7 (58.3) 26 (65) 13 (72.2) 6 (17.6) 5(41.7) 14(35)