CELL SPREADING AND THE REGULATION OF ORNITHINE DECARBOXYLASE

The aim of this study was to investigate the effect of cell spreading on the induction of ornithine decarboxylase and the rate of putrescine uptake in anchorage-dependent and anchorage-independent cells. Platin g non-transformed IEC-6 epithelial cells at high versus low cell densi ty restricted cell spreading from 900 mu m(2) to approximately 140 mu m(2), blunted the transient induction of ornithine decarboxylase activ ity from 202 to 32 pmol (CO2)-C-14/mg protein per hour and reduced the rate of [C-14]putrescine uptake from 46 to 23 pmol/10(5) cells per ho ur, The mean spreading area of the cell population was controlled by c oating tissue culture dishes with the nonadhesive polymer, polyHEMA, O rnithine decarboxylase activity and putrescine uptake correlated with cell spreading with minimal spreading (263 mu m(2)) corresponding to a n 83% decrease in ornithine decarboxylase activity and 51% decrease in the rate of putrescine uptake, Adding the RGD peptide, Gly-Arg-Gly-Gl u-Ser-Pro to the medium of sparsely plated cells resulted in rapid red uctions in cell spreading concomitant with dose-dependent decreases in ornithine decarboxylase activity and putrescine uptake, Finally, mini mizing cell spreading by depriving cells of substratum contact complet ely abolished serum-induced increases in ornithine decarboxylase and r educed the rate of putrescine uptake by 47%. In contrast to IEC-6 cell s, ornithine decarboxylase of neoplastic HTC-116 cells was constitutiv ely expressed with basal and stimulated activity (193 and 982 pmol (CO 2)-C-14/mg protein per hour, respectively) completely independent of c ell adhesion, Putrescine uptake, however, was abolished in the absence of cell adhesion, These data suggest that the induction of ornithine decarboxylase activity and the rate of putrescine uptake correlate wit h spreading of anchorage-dependent IEC-6 cells and that ornithine deca rboxylase activity, but not putrescine uptake, appears to be independe nt of spreading of neoplastic HTC-116 cells.