Independent and differential expression of two isotypes of human Nm23: analysis of the promoter regions of the nm23-H1 and H2 genes.

We isolated genomic clones of two isotypes of human NDP kinase, nm23-H1 and H2. The nm23-H1 and H2 genes located in a tandem array contained 5 exons and most of the splicing sites in the exon-intron junctions of two isotypes were essentially identical. The regulatory elements of nm23-H1 and H2 genes were also analysed. One major and several minor transcriptional initiation sites were detected in the two isotypes by 5' RACE analysis in HeLa cell. We also identified them by means of an RNase protection assay and primer extension analysis. Promoter activities were found in the 5' flanking sequences of the two genes when placed upstream of the chloramphenicol acetyltransferase gene. Transcriptional activities of nm23-H1 and H2 regulatory regions were measured in a series of human cancer lines. The nm23-H1/nm23-H2 gene transcriptional activity ratio varied depending on the cell line. DNA sequencing of these two genes showed that their promoter regions contain distinct binding sites for known transcriptional factors. These studies suggest that the two isotypes of the nm23 genes might be regulated dissimilarly, and in cell type specific manner.