title: NF-kappaB-mediated IAP expression induces resistance of intestinal epithelial cells to apoptosis after polyamine depletion.
abstract: Apoptosis plays a crucial role in maintenance of intestinal epithelial integrity and is highly regulated by numerous factors, including cellular polyamines. We recently showed that polyamines regulate nuclear factor (NF)-kappaB activity in normal intestinal epithelial (IEC-6) cells and that polyamine depletion activates NF-kappaB and promotes resistance to apoptosis. The current study went further to determine whether the inhibitors of apoptosis (IAP) family of proteins, c-IAP2 and XIAP, are downstream targets of activated NF-kappaB and play a role in antiapoptotic activity of polyamine depletion in IEC-6 cells. Depletion of cellular polyamines by alpha-difluoromethylornithine not only activated NF-kappaB activity but also increased expression of c-IAP2 and XIAP. Specific inhibition of NF-kappaB by the recombinant adenoviral vector containing IkappaBalpha superrepressor (AdIkappaBSR) prevented the induction of c-IAP2 and XIAP in polyamine-deficient cells. Decreased levels of c-IAP2 and XIAP proteins by inactivation of NF-kappaB through AdIkappaBSR infection or treatment with the specific inhibitor Smac also overcame the resistance of polyamine-depleted cells to apoptosis induced by the combination of tumor necrosis factor (TNF)-alpha and cycloheximide (CHX). Although polyamine depletion did not alter levels of procaspase-3 protein, it inhibited formation of the active caspase-3. Decreased levels of c-IAP2 and XIAP by Smac prevented the inhibitory effect of polyamine depletion on the cleavage of procaspase-3 to the active caspase-3. These results indicate that polyamine depletion increases expression of c-IAP2 and XIAP by activating NF-kappaB in intestinal epithelial cells. Increased c-IAP2 and XIAP after polyamine depletion induce the resistance to TNF-alpha/CHX-induced apoptosis, at least partially, through inhibition of the caspase-3 activity.
authors.affiliation: Dept. of Surgery, Baltimore Veterans Affairs Medical Center, 10 North Greene St., Baltimore, MD 21201, USA. jwang@smail.umaryland.edu
authors.forename: Tongtong
authors.initials: T
authors.lastname: Zou
authors.forename: Jaladanki N
authors.initials: JN
authors.lastname: Rao
authors.forename: Xin
authors.initials: X
authors.lastname: Guo
authors.forename: Lan
authors.initials: L
authors.lastname: Liu
authors.forename: Huifang M
authors.initials: HM
authors.lastname: Zhang
authors.forename: Eric D
authors.initials: ED
authors.lastname: Strauch
authors.forename: Barbara L
authors.initials: BL
authors.lastname: Bass
authors.forename: Jian-Ying
authors.initials: JY
authors.lastname: Wang
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D002460:Cell Line; D003513:Cycloheximide / Q000494:pharmacology; D006801:Humans; D007413:Intestinal Mucosa / Q000187:drug effects / Q000502:physiology*; D016328:NF-kappa B / Q000502:physiology*; D011073:Polyamines / Q000378:metabolism*; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D011506:Proteins / Q000378:metabolism*; D051381:Rats; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology; D051636:X-Linked Inhibitor of Apoptosis Protein
chemical_list: D016328:NF-kappa B; D011073:Polyamines; D011500:Protein Synthesis Inhibitors; D011506:Proteins; D014409:Tumor Necrosis Factor-alpha; D051636:X-Linked Inhibitor of Apoptosis Protein; C496866:XIAP protein, human; D003513:Cycloheximide