Figure 4

E-cadherin-induced cyclin D1 promoter activation does not require β-catenin/Lef activity. Immunohistochemical analysis of the same tumor section showed that, in most cases, nuclear E-cadherin correlates with nuclear expression of cyclin D1, but not with nuclear expression of β-catenin (a). To determine whether induction of E-cadherin cytoplasmic domain activates β-catenin/Lef response elements, we performed luciferase assays. Neither Ecad-2301 nor Ecad-1904 induced Tcf-responsive (TOP-FLASH) or mutant (FOP-FLASH) reporter constructs. Mutant form of β-catenin was used as a positive control (b). Reporters from Luciferase System 3 (designed for studies of cell growth and proliferation) were used to monitor the activity of multiple signal transduction pathways upon E-cadherin cytoplasmic domain induction. Expression of either Ecad-2301 or Ecad-1904 resulted in a 3.2- and 6.5-fold induction of pAP1-Luc (AP-1 promoter activation) and 3.8- and 2.4-fold pISRE-Luc induction (activation of STAT1/STAT2 transcription factors), respectively. Activation of each reporter was compared with the basal promoter activity of pTAL-Luc, which does not contain any enhancer elements (c). Ecad-2301 and Ecad-1904 overexpression induced cyclin D1 promoter activity (3,6- and 3-fold, respectively) (d).