EXPRESSION OF 15-LIPOXYGENASE BY HUMAN COLORECTAL-CARCINOMA CACO-2 CELLS DURING APOPTOSIS AND CELL-DIFFERENTIATION

We studied arachidonic acid metabolism and the expression of cyclooxyg enase(Cox) and 15-lipoxygenase (15-LO) in the human colorectal carcino ma cell line, Caco-2, which undergo apoptosis and cell differentiation in the presence of sodium butyrate (NaBT), Caco-2 cells expressed ver y low levels of Cox-1 but highly expressed Cox-a. NaBT treatment shift ed the arachidonic acid metabolites by cell lysates from prostaglandin s to 15-hydroxyeicosatetraenoic acid, indicating the presence of a 15- LO. Linoleic acid, an excellent substrate for 15-LO, was metabolized p oorly by the Caco-2 cells, but NaBT treatment shifted metabolism to 15 -LO metabolite, 13(S)-hydroxyoctadecadienoic acid. Caco-2 cells expres sed a 15-LO but only after treatment with NaBT, as determined by North ern blotting. Immunoblotting with anti-human 15-LO antibody detected a 72-kDa band in NaBT-treated Caco-2 cells. Expression of 15-LO mRNA wa s dependent on the duration of NaBT treatment, with the highest expres sion observed between 10 and 24 h, Results from expression and metabol ism studies with arachidonic and linoleic acid cells indicated Cox-a w as responsible for the lipid metabolism in control cells, whereas 15-L O was the major enzyme responsible after NaBT induction of apoptosis a nd cell differentiation. The 15-LO in Caco-2 cells was characterized a s human reticulocyte 15-LO by reverse transcription-polymerase chain r eaction and restriction enzyme analysis. The expression of 15-LO and 1 5-hydroxyeicosatetraenoic acid or 13(S)-hydroxyoctadecadienoic acid fo rmation correlates with cell differentiation or apoptosis in Caco-2 ce lls induced by NaBT, The addition of nordihydroguaiaretic acid, a lipo xygenase inhibitor, significantly increased NaBT-induced apoptosis, wh ereas the addition of indomethacin did not alter NaBT-induced apoptosi s in the Caco-2 cells. However, indomethacin treatment decreased the e xpression of Cox-a in NaBT-treated cells and significantly increased t he expression of 15-LO during NaBT treatment, These studies suggest a role for 15-LO, in addition to Cox-a, in modulating NaBT-induced apopt osis and cell differentiation in human colorectal carcinoma cells.