The central objective of this continuation application is to determine the function of the novel cph oncogene and proto-oncogene, and the role of the activated oncogene in tumorigenesis. The cph oncogene was isolated in the PI's laboratory from chemically-initiated, neoplastic Syrian hamster embryo cells, e carcinogenesis model relevant to human neoplasia. Our previous results demonstrated that cph acts synergistically with ras in the transformation of murine fibroblasts. Results obtained during the present funding period have shown that cph is conserved from yeast to human cells and is expressed in most adult tissues, suggesting that it plays an important role in cellular regulation. In addition we have found that: i) cph is activated by point mutational deletions which result in the synthesis of truncated protein products, ii) the cph proteins have significant global homology to the yeast GDPase, and iii) when overexpressed, cph makes the cells more resistant to various forms of stress. We hypothesize that the activated cph oncogene is a disregulated, hyperactive nucleoside diphosphatase (NDPase) which provides the cells with superior stress- survival functions and proliferative advantage. This hypothesis will be tested by several approaches: 1) Analysis of structural determinants (gain and/or loss of regulatory sequences) of cph transforming activity. 2) Demonstration of the NDPase activity of the cph proteins, by complementation of GDPase-null yeast mutants and by purification, microsequencing and activity assays of native mammalian proteins. 3) Study the mechanism of cph transformation with regard to whether the NDPase activity is required and whether the cph oncoprotein is either mislocalized or interacts with abnormal cellular substrates. 4) Establish the participation of cph in the cellular stress-response pathways. These studies will expand our knowledge on the role of oncogenes in the carcinogenesis process by showing for the first time the contribution of a NDPase to malignancy. The long term goal of this proposal is to extend the knowledge gained to human cells, and to apply it to study the possible role of cph in human neoplasia.