Molecular cloning and characterization of LZIC, a novel gene encoding ICAT homologous protein with leucine zipper domain.

ICAT inhibits the interaction between beta-catenin and TCF transcription factors. As ICAT might be a tumor suppressor gene with the potential to negatively regulate the WNT - beta-catenin - TCF signaling pathway, ICAT related gene in the human genome draft sequence was searched for. Here, the LZIC gene, a novel gene encoding a 190-amino-acid polypeptide with leucine zipper domain and ICAT homologous domain, was cloned and characterized. Amino-acid identity between LZIC and ICAT in the ICAT homologous domain was 38%. The LZIC gene, consisting of at least 8 exons, was located in the human chromosome 1p36.32-pter region. The major 5.2-kb LZIC mRNA and minor 2.1-, 1.6-, and 1.0-kb LZIC mRNAs were expressed almost ubiquitously in normal human tissues. LZIC was expressed in all cancer cell lines examined in this study, and was significantly up-regulated in a gastric cancer cell line MKN74 and 5 cases of primary gastric cancer. As LZIC contains ICAT homologous domain, LZIC might inhibit the interaction between beta-catenin and TCF transcription factors, just like ICAT, and, up-regulation of LZIC in gastric cancer might be due to a negative feed-back mechanism to inhibit the WNT - beta-catenin - TCF signaling pathway.