The aberrant activation of Wnt signaling is a key process in colorectal 
tumorigenesis. Canonical Wnt signaling controls transcription of target genes 
via beta-catenin and T-cell factor/lymphoid enhancer factor family transcription 
factor complex. Arm protein lost in epithelial cancers, on chromosome X 1 
(ALEX1) is a novel member of the Armadillo family which has two Armadillo 
repeats as opposed to more than six repeats in the classical Armadillo family 
members. Here we examine cis-regulatory elements and trans-acting factors 
involved in the transcriptional regulation of the ALEX1 gene. Site-directed 
mutations of a cyclic AMP response element (CRE) and an E-box impaired the basal 
activity of human ALEX1 promoter in colorectal and pancreatic cancer cell lines. 
Moreover, overexpression of CRE-binding protein (CREB) increased the ALEX1 
promoter activity in these cell lines, whereas knockdown of CREB expression 
decreased the expression level of ALEX1 mRNA. Interestingly, luciferase reporter 
analysis and quantitative real-time RT-PCR demonstrated that the ALEX1 promoter 
was up-regulated in a CRE-dependent manner by continuous activation of 
Wnt/beta-catenin signaling induced by a glycogen synthase kinase-3 inhibitor and 
overexpression of beta-catenin. These results indicate that the CRE and E-box 
sites are essential cis-regulatory elements for ALEX1 promoter activity, and 
ALEX1 expression is regulated by CREB and Wntk/beta-catenin signaling.