Antizyme inhibitor: a defective ornithine decarboxylase or a physiological regulator of polyamine biosynthesis and cellular proliferation

ODC (ornithine decarboxylase) is a central regulator of cellular polyamine synthesis. ODC is a highly regulated enzyme stimulated by a variety of growth-promoting stimuli. ODC overexpression leads to cellular transformation. Cellular ODC levels are determined at transcriptional and translational levels and by regulation of its degradation. Here we review the mechanism of ODC degradation with particular emphasis on AzI (antizyme inhibitor), an ODC homologous protein that appears as a central regulator of ODC stability, cellular polyamine homoeostasis and cellular proliferation.