Ornithine decarboxylase (ODC) activity and polyamine (putrescine, spermidine, spermine) concentrations were measured in parallel in enterocyte-like Caco-2 cells maintained under various culture conditions. ODC activity was maximal at the beginning of the exponential growth phase, decreasing dramatically thereafter to a negligible level at confluency (day 9). Kinetic studies performed on day 3 revealed the presence of a single enzyme with a K , around 200 FM and a V, , , of about 2 nmol COz released/h/mg protein. Similar values were obtained in both serum-supplemented and transferrin/selenium (TS)-defined culture media, indicating that ODC kinetic parameters are not affected by any factors present in serum. Polyamine concentrations were maximal on day 5. By day 9, they returned to initial levels and remained at these fairly high values until day 21. Since we have previously shown (Jumarie and Malo, 1994, In Vitro Cell. Dev. Biol., 3OA3753-760) that triiodothyronine (T,) stimulates differentiation but not proliferation of Caco-2 cells maintained in TS-defined medium, we investigated if it induces differentiation by a polyamine-dependent mechanism. Shortand long-term measurements revealed similar ODC activity and polyamine levels whether TI was present or not in the culture medium. These results clearly demonstrate that polyamine synthesis is more likely to be associated with Caco-2 cell proliferation, and that the T, effect on Caco-2 cell differentiation does not involve polyamine biosynthesis. Moreover, our data show that ODC activity is not solely regulated by intracellular polyamine concentration. o 1995 WiIey-Liss, inc.
Spermidine, spermine, and their precursor putrescine are ubiquitous polyamines found in both prokaryotic and eukaryotic cells (Pegg and McCann, 1982). Pu-