Cyclooxygenase‐2 and RhoA modulates E‐cadherin expression through the transcriptional repressor ZEB1

ZEB1 is a potent transcriptional repressor of the adherens junction (AJ) core protein, E‐cadherin. Previously it has been shown that cyclooxygenase‐2 (COX‐2) activates the small GTPase RhoA which in turn down‐regulates E‐cadherin to disrupt AJ and increase motility of colon carcinoma cells. In this study we examine the possibility that an increase in RhoA activity decreases E‐cadherin expression levels utilizing the ZEB1 pathway in two human colon carcinoma cell lines, HT‐29 and HCT‐15. Total protein and mRNA were isolated from both cell lines either expressing constitutively active (CA) or dominant negative (DN) RhoA. Using qRT‐PCR, both E‐cadherin and ZEB1 mRNA levels were monitored, whereas E‐cadherin protein levels were determined by western blot analysis. The same experiments were also conducted on parental HT‐29 and HCT‐15 cells as well as cells overexpressing COX‐2. In all experiments, RhoA‐CA or COX‐2 increased ZEB1 expression and decreased E‐cadherin expression by at least two‐fold. Expression levels of both ZEB1 and E‐cadherin were indistinguishable from wild type in those cells expressing RhoA‐DN. Also, inhibition of RhoA restored both ZEB1 and E‐cadherin expression levels to those of wild type. In conclusion, COX‐2 and RhoA mediates AJ formation by down‐regulating E‐cadherin expression through the ZEB1 transcriptional repressor pathway.