ORNITHINE DECARBOXYLASE OVEREXPRESSION IN MOUSE 10T1 2 FIBROBLASTS - CELLULAR-TRANSFORMATION AND INVASION/

Background: Ornithine decarboxylase (ODC) plays a pivotal role in the synthesis of polyamines, a group of chemical compounds that are essent ial for cell growth. Recent reports have shown that ODC overexpression may be involved in malignant transformation of immortalized NIH 3T3 c ells, We have demonstrated that ODC-overproducing mouse breast cancer cells are more invasive in vitro than control cells. However, little i nformation is available concerning the relationship between ODC overex pression, tumor invasion, and metastasis and the signal transduction p athways involved in ODC-induced transformation and invasion, Purpose: Our purpose was twofold: 1) to determine whether ODC overexpression is directly involved in tumor cell invasion and 2) to determine whether ODC overexpression induces mitogen-activated protein (MAP) kinase acti vities that are associated with cell growth and transformation. Method s: We transfected C3H clone 8 mouse 10T1/2 fibroblasts with an express ion vector that carries a complementary DNA encoding rat ODC, Neomycin -resistant cells that overproduced ODC (4-6.5 times the control levels ) were isolated. The transformed phenotype of these cells was determin ed by assessing colony formation and anchorage-independent growth in s oft agar. The invasiveness of the cells was studied by means of an inv asion assay that used Matrigel-coated filters in Boyden chambers. The MAP kinase activity of the cells was assayed by an in-gel kinase assay , using myelin basic protein as the substrate, Results: Overexpression of ODC induced not only cell transformation and anchorage-independent growth in soft agar but also invasiveness through a Matrigel-coated f ilter. The ODC-overproducing transfectants showed enhanced MAP kinase activity that paralleled the magnitude of cell invasiveness, Conclusio ns: ODC plays a pivotal role not only in cell transformation but also in cancer cell invasion. ODC overexpression enhanced MAP kinase activi ty. Implications: Our results demonstrate a connection between the pol yamine/ODC and the MAP kinase signal transduction pathways and suggest that MAP kinase may play a pivotal role in ODC-induced cell transform ation and invasion.