Polyamines are ubiquitous cellular components whose functions are not known precisely although they are clearly essential for cell growth and appear to be involved in neoplastic transformation. Inhibitors of polyamine formation have great potential as therapeutic agents but a more detailed knowledge of the consequences of perturbing polyamine metabolism is needed before the full potential of these compounds can be realized. The planned experiments are centered on studies of antizyme (AZ), a protein that regulates ODC and polyamine transport and of two key enzymes in polyamine metabolism [ornithine decarboxylase (ODC) and spermidine/spermine A/1-acetyltransferase (SSAT)]. They build on studies carried out in the previous period of support that include the generation of transgenic mice in which these proteins have been over-expressed from specific promoters. In these studies, it was found: (a) that transgenic expression of AZ blocks carcinogenesis in a range of tissues in response to a variety of carcinogenic stimuli; (b) that targeted transgenic expression of SSAT increased the size and tumor incidence and progression to carcinomas of skin tumors after a two stage initiator plus promoter protocol; and (c) that there appears to be a compensatory mechanism that allows basal polyamine synthesis to occur even in the presence of enhanced levels of AZ. There are 2 specific aims.
Aim (1) will use mice expressing AZ from the K5 and K6 promoters to understand the mechanism by which AZ acts as a tumor suppressor. Experiments will be carried out to determine whether the anti-tumor effects of AZ are due solely to its ability to block increases in cellular polyamines; to determine the role of p53 in the response to AZ; to identify gene products altered by AZ expression leading to the reduction in tumor growth; and to determine whether there is a form of ODC resistant to AZ or another compensatory mechanism that occurs to allow basal polyamine levels to be maintained.
Aim 2 will use mice expressing SSAT from the K6 promoter to investigate the role of SSAT in promoting skin tumor development. The experiments will investigate three possible explanations for this effect. These are: (a) oxidative stress resulting from the activation of the SSAT/polyamine oxidase pathway; (b) the alteration in relative polyamine levels produced by SSAT; and (c) other SSAT functions not directly involved in polyamine metabolism. These experiments will extend knowledge of the control of mammalian polyamine levels, the role of polyamines in cellular physiology and the involvement of polyamines in carcinogenesis. They will also facilitate the development of inhibitors of polyamine biosynthesis including inducers of AZ as antitumor and chemopreventive agents. The knowledge generated in this research will aid in the prevention and treatment of cancer. ? ?
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