Polyamine depletion induces rapid NF-κB activation in IEC-6 cells

The proliferation of the rat intestinal mucosal IEC-6 cell line requires polyamines, whose synthesis is catalyzed by the enzyme ornithine decarboxylase (ODC). ODC inhibition leads to polyamine depletion, as well as inhibition of both cell proliferation and apoptosis by regulating gene expression. The NF-kappaB transcription factor regulates genes involved in apoptotic, immune, and inflammatory responses. In the present study we tested the hypothesis that NF-KB is activated following ODC inhibition. We found that the inhibition of ODC by a-difluoromethylornithine (DFMO) resulted in a similar to 50% decrease in intracellular putrescine levels within Ih. NF-KB is activated by DFMO through the degradation of the inhibitory protein I kappaB alpha that sequesters NF-kappaB in the cytoplasm. The DFMO-induced NF-KB complexes contain the p65 and p50 members of the Rel protein family. DFMO-induced NF-kappaB activation was accompanied by the translocation of p65 from the cytoplasm into the nucleus. DFMO selectively inhibited a gene reporter construct dependent on the kappaB site present in the HLA-B7 gene. In contrast, DFMO had no effect on a gene reporter construct dependent on the kappaB site present in the interleukin-8 gene. Thus, we report that ODC inhibition activates the NF-KB transcription factor, which may mediate the altered physiological state of intestinal cells that occurs following polyamine depletion.