Antizyme forms originating from the first start site of the AZ-1 gene

The polyamines are small, organic molecules that are essential for normal cell physiology and growth. Polyamine levels are tightly regulated in cells, and perturbations in this homeostasis are associated with disease, the most notable of which is cancer. Antizyme is a small, labile protein central to the regulation of polyamines and a likely candidate to mediate polyamine depletion as cancer therapy. Unfortunately, very little is known about this regulatory molecule. Antizyme exists in several different forms in cells that may reflect variable function or cellular localization.; To sort out the origin, modification, function and localization of the various forms of antizyme, a cell line with an inducible AZ-1 construct that can only result in protein synthesized from the first start site was produced. This construct resulted in two forms of antizyme. One of the forms appears to be derived by proteolytic truncation of the N-terminus. These forms of antizyme behave as native antizyme with respect to activity in binding and inhibiting ODC, as well as down-regulating the polyamine transport system. Surprisingly, in these studies, antizyme localization was shown to be either nuclear or nuclear-excluded in individual cells and this localization may change in response to some physiological signal. Further, as shown previously in other systems and cell lines, long-term induction of antizyme results in reduced cell growth and appears to be the result of polyamine depletion.; Characterization of the N-terminal truncation of antizyme was attempted by various means. Even though characterization of this modification proved elusive, these results do provide clues as to what the modification might or might not be. Contrary to previously suggested models, the processing does not appear to be associated with mitochondrial transport, but is due to some component of the post-mitochondrial pellet. Further, although the modification could be the result of a proteosomal component, it has been demonstrated here that it is not the result of partial degradation by the 26S proteosome. Presented in this thesis are data that shed new light on the origin and modification of the different forms of antizyme in relation to function and cytolocalization.