title: Regulation of cell proliferation by the antizyme inhibitor: evidence for an antizyme-independent mechanism.
abstract: The antizyme inhibitor was discovered as a protein that binds to the regulatory protein antizyme and inhibits the ability of antizyme to interact with the enzyme ornithine decarboxylase (ODC). Blocking antizyme activity subsequently leads to increased intracellular levels of ODC and increased ODC enzymatic activity. We now report that antizyme inhibitor is a positive modulator of cell growth. Overexpression of antizyme inhibitor in NIH-3T3 mouse fibroblasts or in AT2.1 Dunning rat prostate carcinoma cells resulted in an increased rate of cell proliferation and an increase in saturation density of the cultured cells. This was accompanied by an increase in intracellular levels of the polyamine putrescine. In AT2.1 cells, antizyme inhibitor overexpression also increased the ability of the cells to form foci when grown under anchorage-independent conditions. In order to determine the role of antizyme on antizyme inhibitor activity we created an antizyme inhibitor mutant, AZI(Delta117-140), which lacks the putative antizyme-binding domain. We show that this mutant fails to bind to antizyme, but remains capable of inducing increased rates of cell proliferation, suggesting that antizyme inhibitor has antizyme-independent functions. Silencing antizyme inhibitor expression leads to diminished levels of cyclin D1 and to reduced cell proliferation. Antizyme inhibitor is capable of preventing cyclin D1 degradation, and this effect is at least partially independent of antizyme. We show that wild-type antizyme inhibitor and the AZI(DeltaY) mutant are capable of direct interaction with cyclin D1 suggesting a potential mechanism for the antizyme-independent effects. Together, our data suggest a novel function for antizyme inhibitor in cellular growth control.
authors.affiliation: Program in Vascular Biology and Department of Surgery, Children's Hospital, Boston, MA 02115, USA.
authors.forename: Sonia W
authors.initials: SW
authors.lastname: Kim
authors.forename: Ursula
authors.initials: U
authors.lastname: Mangold
authors.forename: Carol
authors.initials: C
authors.lastname: Waghorne
authors.forename: Arian
authors.initials: A
authors.lastname: Mobascher
authors.forename: Lisa
authors.initials: L
authors.lastname: Shantz
authors.forename: Jacqueline
authors.initials: J
authors.lastname: Banyard
authors.forename: Bruce R
authors.initials: BR
authors.lastname: Zetter
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D004789:Enzyme Activation / Q000187:drug effects; D005347:Fibroblasts / Q000187:drug effects; D005786:Gene Expression Regulation / Q000235:genetics; D020868:Gene Silencing / Q000187:drug effects; D051379:Mice; D009154:Mutation; D041681:NIH 3T3 Cells; D009955:Ornithine Decarboxylase / Q000235:genetics / Q000378:metabolism*; D065108:Ornithine Decarboxylase Inhibitors; D011506:Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000494:pharmacology; D051381:Rats; D013329:Structure-Activity Relationship
chemical_list: D065108:Ornithine Decarboxylase Inhibitors; D011506:Proteins; D034741:RNA, Small Interfering; C031017:ornithine decarboxylase antizyme; D009955:Ornithine Decarboxylase