Overexpression Transformation of NIH/3T3 Cells by Ornithine Decarboxylase

Ornithine decarboxylase (ODO plays a rate-limiting role in polyamine biosynthesis and is intimately associated with cell proliferation and func tion. Although elevated levels of ODC mRNA, protein, and enzyme activity are consistently detected in transformed cells and tumors, the question remains as to whether ODC gene overexpression has a causative role in tumorigenesis. We have stably transfected MH/3T3 fibroblasts with an expression construct containing human ODC complementary DNA under Iranscriptional control of the human ß-actinpromoter. Cells transfected with the ß-actin/ODC DNA construct, designated NODI cells, and control transfectants, termed M K cells, were analyzed for ODC gene expression and cell growth characteristics. ODC activity and mRNA levels were elevated 3-6-fold in NODC cells relative to M K cells. MODC cells, in contrast to M K control cells, are not contact inhibited, exhibit anchorageindependent growth, cycle more rapidly, and induce tumors in nude mice more efficiently and rapidly. These results directly establish a causative role for the misregulation of ODC gene expression in the acquisition of a transformation phenotype and provide a model to examine the interaction of ODC and other gene products in neoplastic development.