ORNITHINE DECARBOXYLASE ACTIVITY IS ASSOCIATED WITH PROLIFERATION BUTNOT WITH T-3-INDUCED DIFFERENTIATION OF CACO-2 CELLS

Ornithine decarboxylase (ODC) activity and polyamine (putrescine, sper midine, spermine) concentrations were measured in parallel in enterocy te-like Caco-2 cells maintained under various culture conditions. ODC activity was maximal at the beginning of the exponential growth phase, decreasing dramatical ly thereafter to a negligible level at confluen cy (day 9). Kinetic studies performed on day 3 revealed the presence o f a single enzyme with a K-m around 200 mu M and a V-max of about 2 nm ol CO2 released/h/mg protein. Similar values were obtained in both ser um-supplemented and transferrin/selenium (TS)-defined culture media, i ndicating that ODC kinetic parameters are not affected by any factors present in serum. Polyamine concentrations were maximal on day 5. By d ay 9, they returned to initial levels and remained at these fairly hig h values until day 21. Since we have previously shown (Jumarie and Mal e, 1994, In Vitro Cell. Dev. Biol., 30A:753-760) that triiodothyronine (T-3) stimulates differentiation but not proliferation of Caco-2 cell s maintained in TS-defined medium, we investigated if it induces diffe rentiation by a polyamine-dependent mechanism. Short- and long-term me asurements revealed similar ODC activity and polyamine levels whether T-3 was present or not in the culture medium. These results clearly de monstrate that polyamine synthesis is more likely to be associated wit h Caco-2 cell proliferation, and that the T-3 effect on Caco-2 cell di fferentiation does not involve polyamine biosynthesis. Moreover, our d ata show that ODC activity is not solely regulated by intracellular po lyamine concentration. (C) 1995 Wiley-Liss, Inc.