Biochemical cross-talk: phosphotransferase and dna binding activity of nucleoside diphosphate kinase

Abstract

Biochemical cross-talk: Phosphotransferase and DNA-binding activity of nucleoside diphosphate kinase Deregulated expression of proto-oncogene c-MYC has been implicated in several cancers. Transcriptional regulation of c-MYC is a complex process involving use of multiple promoters and factors. Using chromatin immunoprecipitation (ChIP) assay this study demonstrates that human nucleoside diphosphate kinase-B or NM23-H2, a metabolic enzyme which is a member of the metastasis suppressor family (non-metastatic 23) physically occupies the c- MYC promoter in multiple cancer cell lines. Moreover, results in present study indicate that NM23-H2 binding to c-MYC promoter is mediated through a previously characterized unusual DNA structural motif present in the nuclease hypersensitive element (NHE III1) of c-MYC promoter. Taken together results in this study suggest a novel regulatory mechanism for c-MYC which entails its regulation by a suppressor of metastasis, NM23-H2. Apart from acting as a NDP kinase, NM23-H2 has also been shown to act as an endonuclease in vitro. ChIP assays using NM23-H2H118C and NM23-H2K12A mutants suggest that endonuclease and enzymatic activities of NM23-H2 are independent of its transcriptional regulatory activity. Furthermore taking case specific examples this study showed that G-rich promoter of CCR5 gene is a direct target of NM23-H2 under physiological conditions. ChIP-on chip method was used to find out the repertoire of binding sites of NM23-H2 throughout the human gene promoters. Results indicate 935 DNA binding sites for NM23-H2 corresponding to 404 annotated promoters. These 404 genes were enriched within the GO categories of biological processes: regulation of cellular physiological processes, regulation of apoptosis, embryonic development, and G1/S transition in mitotic cell cycle (P < 0.005). It has been observed that nucleoside diphosphate kinase from M. tuberculosis (mNdK) localizes within nuclei of HeLa and COS-1 cells and also nicks chromosomal DNA in situ.