NF-kappa B activation and susceptibility to apoptosis after polyamine depletion in intestinal epithelial cells

The maintenance of intestinal mucosal integrity depends on a balance betwee n cell renewal and cell death, including apoptosis. The natural polyamines, putrescine, spermidine, and spermine, are essential for mucosal growth, an d decreasing polyamine levels cause G(1) phase growth arrest in intestinal epithelial (IEC-6) cells. The present study was done to determine changes i n susceptibility of IEC-6 cells to apoptosis after depletion of cellular po lyamines and to further elucidate the role of nuclear factor-kappaB (NF-kap paB) in this process. Although depletion of polyamines by alpha -difluorome thylornithine (DFMO) did not directly induce apoptosis, the susceptibility of polyamine-deficient cells to staurosporine (STS)-induced apoptosis incre ased significantly as measured by changes in morphological features and int ernucleosomal DNA fragmentation. In contrast, polyamine depletion by DFMO p romoted resistance to apoptotic cell death induced by the combination of tu mor necrosis factor-alpha (TNF-alpha) and cycloheximide. Depletion of cellu lar polyamines also increased the basal level of NF-kappaB proteins, induce d NF-kappaB nuclear translocation, and activated the sequence-specific DNA binding activity. Inhibition of NF-kappaB binding activity by sulfasalazine or MG-132 not only prevented the increased susceptibility to STS-induced a poptosis but also blocked the resistance to cell death induced by TNF-alpha in combination with cycloheximide in polyamine-deficient cells. These resu lts indicate that 1) polyamine depletion sensitizes intestinal epithelial c ells to STS-induced apoptosis but promotes the resistance to TNF-alpha -ind uced cell death, 2) polyamine depletion induces NF-kappaB activation, and 3 ) disruption of NF-kappaB function is associated with altered susceptibilit y to apoptosis induced by STS or TNF-alpha. These findings suggest that inc reased NF-kappaB activity after polyamine depletion has a proapoptotic or a ntiapoptotic effect on intestinal epithelial cells determined by the nature of the death stimulus.