The Role of NDP kinases in Membrane Signal Transduction

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I.Signal transduction and NDP kinasePossible involvement of NDP kinase in those signal transduction systems has been originally proposed based on the observation that hormones can activate effector adenylyl cyclase in rat liver and human platelet membranes in the presence of GDP as observed for GTP.NDP kinase seems to act as a receptor activation-mediated GTP supply machinery for the G proteins in these signal transduction systems.The relationship between NDP kinase and signal transduction systems was further investigated by Dr.Orlov in TMIG using bovine retinal rod outer segment (ROS) preparations where components of signal transduction are extremely concentrated compared with other tissues.The soluble NDP kinase in the ROS preparations was found to interact with the ROS membranes in a pH,monovalent and divalent cations dependent manner.The NDP kinase bound to the membranes under acidic pH and low ionic strenght was released by the presence of GTP or its analogs (GTPgammaS,GppNHp).The results demonstrated that transducin (Gt) seems to be involved in the high affinity, GTP-sensitive interaction of the soluble NDP kinase with the bleached ROS membranes.II.Participation in the international workshop and visiting to NIHDrs.Kimura and Ishikawa participated in the first international workshop held in Paris at Pasteur Institute and gave talks entitled "The role of NDP kinases/nm23 in cellular functions "and" Rat NDP kinase isoform genes : structures and expression", respectively.It should be noted that Dr.Kimura chaired a session in the meeting.They then visited with Dr.Liotta at NIH in the U.S.to exchange information on the role of NDP kinase/nm23 as a candidate tumor metastasis suppressor.The data obtained with NDP kinase alpha- and beta-transfected cells in relation to their metastatic potential were discussed.