Writ inhibitory factor-1 (WIF-1) is a secreted antagonist of Wnt signaling and functions by directly binding to Wnt ligands in the extracellular space. Here we report the identification of the 5' promoter region (similar to1.5 kb) of the human WIF-1 gene. Functional analysis of this region shows that a whole fragment displays high basal promoter activity in different cell lines, while the truncated forms do not, indicating that integrity of the WIF-1 promoter region may be important for WIF-1 activity. Moreover, we found that the expression level of beta-catenin in cancer cell lines correlates with the WIF-1 promoter activity, suggesting that the WIF-1 promoter may be regulated by the Wnt/beta-catenin pathway and may function in a negative feedback manner. Our results also suggest that a methylated CpG island, which we observed recently in human lung cancer, lies within the functional WIF-1 promoter region and therefore bears the importance of the methylation-status of this CpG island as an important key in Wnt activation in human cancer. (C) 2004 Elsevier Inc. All rights reserved.