Increased expression of nucleoside diphosphate kinases/nm23 in human diploid fibroblasts transformed by SV40 large T antigen or ⁶⁰Co irradiation

When the expression levels of nucleoside diphosphate (NDP) kinase/nm23 were examined in four human normal diploid fibroblast cell lines in comparison with their corresponding immortalized cells transformed by SV40 large T antigen or ⁶⁰Co irradiation, mRNA levels of the two isoforms (NDP kinase A/nm23-H1, NDP kinase B/nm23-H2) were increased in the immortalized cell lines. The increase was found to be associated with increased translation products. Furthermore, the cell extracts prepared from these immortalized cell lines demonstrated slightly higher enzyme activity than those from their normal counterparts. Neither the growth state nor the in vitro aging largely affected their expression in a normal cell line (TIG-3) examined. The results suggest possible involvement of NDP kinases/nm23 in acquiring an infinite growth property of these cells.