Translocation of ornithine decarboxylase to the surface membrane during cell activation and transformation

Ornithine decarboxylase (ODC) is highly up-regulated in proliferating and t ransforming cells. Here we show that upon induction, an initial cytosolic i ncrease of ODC is followed by translocation of a fraction of the enzyme to the surface membrane. ODC membrane translocation is mediated by a p47(phox) membrane-targeting motif-related sequence, as indicated by reduced ODC act ivity in the membrane fraction of cells treated with a competing, ODC-deriv ed (amino acids 165-172) peptide, RLSVKFGA, which is homologous to the p47( phox) membrane-targeting sequence. p47(phox) membrane translocation is know n to be dependent on the phosphorylation of the targeting motif, Analogousl y, overexpressed ODC,S167A, a mutant ODC lacking the putative phosphorylati on site Ser67, is unable to move to the surface membrane. Cells blocked wit h the RLSVKFGA peptide showed defective transformation, indicating that the motif-mediated translocation of ODC is prerequisite to its biological func tion. Constitutive targeting of ODC to the membrane using a plasmid encodin g the chimeric protein, wild-type ODC with C-terminal linkage to the farnes ylation motif of K-ras, caused impaired cytokinesis with an accumulation of polykaryotic cells, Impaired cytokinesis confirms that ODC is involved in mitotic cytoskeletal rearrangement events and pinpoints the importance of r elevant membrane targeting to its physiological function.