Maturation-dependent sequential expression of interferon regulatory factor-1 and inducible nitric oxide synthase in cultured human enterocytes

We tested the hypothesis that inducible nitric oxide (NO) synthase (iNOS) a nd interferon regulatory factor 1 (IRF-1), a trans-acting factor in iNOS tr anscriptional activation, are maturation-dependently expressed in cytokine- stimulated human enterocytes. Caco-2BBe cells, at varying stages of maturat ion, were stimulated with IL-1 beta and IFN-gamma. Cytokine stimulation of 3-day-old undifferentiated Caco-2BBe cells induced tow levels of NO product ion, iNOS and IRF-1 immunoreactivity, iNOS and IRF-1 mRNA expression, and i NOS activity, whereas 24-day-old mature cells responded with a large and pr olonged activation of iNOS and IRF-1 expression. The basis for this differe nce was accounted in part by the relatively greater iNOS transcription rate in 24- vs. 3-day-old cells. Sequential expression of IRF-1 followed by iNO S mRNA occurred in both 3- and 24-day-old cells. We conclude that enterocyt e maturation profoundly alters the magnitude and duration of human iNOS and IRF-1 expression in response to cytokine stimulation. The differences in i NOS mRNA levels between the immature and mature cells are only partially ex plained by difference in transcriptional rates, implying that post-transcri ptional regulation may also be influenced by the state of enterocyte matura tion. Induction of IRF-1 expression precedes and parallels the level of iNO S expression at all stages of maturation. We propose that IRF-1 may modulat e the expression of cytokine-induced iNOS activity in differentiating enter ocytes.