Interaction between cyclooxygenase-2, Snail, and E-cadherin in gastric cancer cells

Figure 1 Effect of cyclooxygenase-2 knockdown on the expression of nuclear factor-κB, Snail, and E-cadherin in gastric cancer cells. Among the four human gastric cancer cell lines, SGC-7901 has the highest expression level of cyclooxygenase-2 (COX-2) at mRNA (A) and protein level (B). Thus, this cell line was used to study the regulatory effect of COX-2 on nuclear factor-κB (NF-κB), Snail, and E-cadherin. Successful knockdown of COX-2 was confirmed at mRNA (C) and protein (D) levels. Down-regulation of COX-2 led to a reduction of NF-κB subunit p65 and Snail but an increased E-Cadherin, both at the mRNA (E) and protein (F) levels. mRNA expression was examined by quantitative polymerase chain reaction (qPCR) and expressed as a relative arbitrary unit against that of β-actin. Protein expression was examined by Western blot (^aP < 0.05 vs their respective controls).

Figure 2 Effect of nuclear factor-κB knockdown on the expression of cyclooxygenase-2, Snail, and E-cadherin in SGC-7901 cells. Cells transfected with specific siRNA against nuclear factor-κB (NF-κB) subunit p65 (p65-siRNA) showed a marked down-regulation of p65 at mRNA (A) and protein (B) levels. p65-siRNA led to a reduction of Snail but an increased E-cadherin, both at the mRNA (C) and protein (D) levels. However, p65-siRNA mediated down-regulation of NF-κB did not significantly alter the expression of COX-2, both at the mRNA (C) and protein (D) levels. mRNA expression was examined by polymerase chain reaction (qPCR) and expressed as a relative arbitrary unit against that of β-actin. Protein expression was examined by Western blot. (^aP < 0.05 vs their respective controls).

Figure 3 Down-regulation of nuclear factor-κB by p65-siRNA reversed the regulatory effect of celecoxib and prostaglandin E2 on Snail and E-cadherin in SGC-7901 cells. Treatment of SGC-7901 cells with celecoxib led to a reduced expression of Snail but an increased expression of E-cadherin both at mRNA (A) and protein (B) levels. In contrast, treatment of SGC-7901 cells with prostaglandin E2 (PGE2) led to an increased Snail and a decreased E-cadherin at mRNA (A) and protein (B) levels. However, when the cells were pre-treated with p65-siRNA, the observed effects of Celecoxib and PGE2 were reversed (A, B). mRNA expression was examined by polymerase chain reaction (qPCR) and expressed as a relative arbitrary unit against that of β-actin. Protein expression was examined by Western blot (^aP < 0.05 vs their respective controls).