Studies on the mechanism of NDP kinase/nm23 and its interacting proteins

点击翻译按钮获取中文摘要

The role of nucleoside diphosphate (NDP) kinases in cell growth, differentiation, and tumor metastasis was investigated. The essential role of NDP kinase in cell growth was validated by coupling between reduced NDP kinase levels induced by antisense oligonucleotides and the suppression of proliferative activity of a cultured cell line. On the other hand, the enhanced NDP kinase accumulation was demonstrated in the matured osteoblasts in vivo and in vitro by immunohistochemistry. In PC12D cells, neurite outgrowth took place in NDP kinase β-transfected clones without differentiation induders, which was accompanied by prologation of doubling time. Neurite outgrowth triggered by nerve growth factor and a cyclic AMP analog was down-regulated upon forced expression of inactive mutant NDP kinase by virtue of a dominant negative effect. NDP kinase α-transfected rat mammary adenocarcinoma cells (MTLn3) and nm23-H2-transfected human oral squamous cell carcinoma cells (LMF4) manifested reduced me … More tastatic potential and were associated with an altered sensitivity to environmental factors such as motility and growth factors. Considering the housekeeping nature of NDP kinases, it is plausible that there is a mechanism that keeps NDP kinase protein levels constant to maintain their function in a variety of cells. To investigate this problem, we employed a tetracycline-controlled expression system allowing the expression of exogenously introduced NDP kinase in a tetracyclin-dependent manner in a cell and attempted to determine whether endogenous NDP kinase protein levels are affected by the expression of exogenous NDP kinase. The results demonstrated that the endogenous NDP kinase levels are suppressed by the co-expression of exogenous NDP kinase, implying the presence of a negative feedback regulation of NDP kinase genes by their protein products. Taken together, NDP kinase isoforms appear to elicit both their own respective and common effects. They may have an ability to lead cells to both proliferative and differentiated states by modulating responsiveness to environmental factors, but their fate seems to depend on their surrounding milieu. Less