Genomic structure of the human NLK (nemo-like kinase) gene and analysis of its promoter region

Recent search revealed that nemo-like kinase (NLK) was identified as a negative regulator of the wingless type signal cascade in Xenopus and in Caenorhabditis elegans. NLK phosphorylates T-cell factor (TCF)/lymphoid enhancer-binding factor (LEF) and interferes with binding of the β-catenin-TCF/LEF complex to its TCF target site. After we constructed bacterial artificial chromosome clone contig covering more than 45-kb NLK chromosomal gene, genomic cloning revealed that the human NLK gene consists of 11 exons interrupted by ten introns; its translation-initiation site is within exon 1, and the termination codon and polyadenylation signal lie in exon 11. The 289 amino acids of its kinase domain extend from the 3′-portion of exon 1 to the 5′-portion of exon 9, and show a high degree of similarity in amino acid sequence to kinase domains of extracellular-signal regulated kinase 5 (mitogen activated protein kinase 7) and cyclin-dependent kinases, although the positions of introns among those genes are not conserved. Reverse transcription polymerase chain reactions analysis in various tissues showed that NLK is expressed ubiquitously. Analysis of its promoter region by luciferase reporter assays in transfected HeLa and NIH3T3 cells revealed that an upstream region from −487 to +33 bp of the NLK gene contains significant promoter activity. This 5′-flanking region probably contains the cis-acting element of NLK. In addition, our mutation screening showed that NLK was not a mutational target in breast and colorectal tumor cells.