Ornithine Decarboxylase Overexpression in Mouse 10T12 Fibroblasts: Cellular Transformation and Invasion

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Abstract
Background: Ornithine decarboxylase (ODC) plays a pivotal role in the synthesis of polyamines, a group of chemi cal compounds that are essential for cell growth. Recent reports have shown that ODC overexpression may be in volved in malignant transformation of immortalized NIH 3T3 cells. We have demonstrated that ODC-overproduc ing mouse breast cancer cells are more invasive in vitro than control cells. However, little information is available concerning the relationship between ODC overexpression, tumor invasion, and metastasis and the signal transduc tion pathways involved in ODCtransformation and invasion. Purpose: Our purpose was twofold: 1) to determine whether ODC overexpres sion is directly involved in tumor cell invasion and 2) to determine whether ODC overexpression induces mitogen activated protein (MAP) kinase activithat are associated with cell growth and transformation. Methods: We transfected C3H clone 8 mouse 10T12 fibroblasts with an expression vector that carries a complementary DNA en coding rat ODC. Neomycin-resistant cells that overproduced ODC (4–6.5 times the control levels) were isolated. The transformed phenotype of these cells was determined by assessing colony formation and anchorage independent growth in soft agar. The invasiveness of the cells was studied by means of an invasion 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: Overexpres sion of ODC induced not only cell transformation and anchorage-inde pendent growth in soft agar but also invasiveness through a Matrigel-coated filter. The ODC-overproducing transshowed enhanced MAP kinase activity that paralleled the magnitude of cell invasiveness. Conclusions: ODC plays a pivotal role not only in cell transformation but also in cancer cell invasion. ODC overexpression enhanced MAP kinase activity. Implications: Our results demonstrate a con nection between the polyamineand the MAP kinase signal transduc tion pathways and suggest that MAP kinase may play a pivotal role in ODC induced cell transformation and inva sion. [J Natl Cancer Inst 1997;89:567 71]