title: Interleukin-11 antagonizes Fas ligand-mediated apoptosis in IEC-18 intestinal epithelial crypt cells: role of MEK and Akt-dependent signaling.
abstract: Interleukin-11 (IL-11) displays epithelial cytoprotective effects during intestinal injury. Antiapoptotic effects of IL-11 have been described, yet mechanisms remain unclear. Fas/CD95 death receptor signaling is upregulated in ulcerative colitis, leading to mucosal breakdown. We hypothesized that IL-11 inhibits Fas ligand (FasL)-mediated apoptosis in intestinal epithelia. Cell death was monitored in IEC-18 cells by microscopy, caspase and poly(ADP-ribose) polymerase cleavage, mitochondrial release of cytochrome c, and abundance of cytoplasmic oligonucleosomal DNA. RT-PCR was used to monitor Fas, cIAP1, cIAP2, XIAP, cFLIP, survivin, and Bcl-2 family members. Fas membrane expression was detected by immunoblot. Inhibitors of JAK2, phosphatidylinositol 3-kinase (PI3-kinase), Akt 1, MEK1 and MEK2, and p38 MAPK were used to delineate IL-11's antiapoptotic mechanisms. IL-11 did not alter Fas expression. Pretreatment with IL-11 for 24 h before FasL reduced cytoplasmic oligonucleosomal DNA by 63.2%. IL-11 also attenuated caspase-3, caspase-9, and poly(ADP-ribose) polymerase cleavage without affecting expression of activated caspase-8 p20 or cytochrome c release. IL-11 did not affect mRNA expression of the candidate antiapoptotic genes. The MEK1 and MEK2 inhibitors U-0126 and PD-98059 significantly attenuated the protection of IL-11 against caspase-3 and caspase-9 cleavage and cytoplasmic oligonucleosomal DNA accumulation. Although Akt inhibition reversed IL-11-mediated effects on caspase cleavage, it did not reverse the protective effects of IL-11 by DNA ELISA. We conclude that IL-11-dependent MEK1 and MEK2 signaling inhibits FasL-induced apoptosis. The lack of reversal of the IL-11 effect on DNA cleavage by Akt inhibition, despite antagonism of caspase cleavage, suggests that IL-11 inhibits caspase-independent cell death signaling by FasL in a MEK-dependent manner.
authors.affiliation: Department of Medicine, Gastrointestinal Diseases Research Unit, Queen's University, Kingston, Ontario, Canada.
authors.forename: Kaitlin M
authors.initials: KM
authors.lastname: Naugler
authors.forename: Kathy A
authors.initials: KA
authors.lastname: Baer
authors.forename: Mark J
authors.initials: MJ
authors.lastname: Ropeleski
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D053148:Caspase 3 / Q000378:metabolism; D053453:Caspase 9 / Q000378:metabolism; D061945:Caspase Inhibitors; D002462:Cell Membrane / Q000187:drug effects; D002478:Cells, Cultured; D003600:Cytosol / Q000378:metabolism; D003627:Data Interpretation, Statistical; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004847:Epithelial Cells / Q000187:drug effects*; D053222:Fas Ligand Protein / Q000037:antagonists & inhibitors*; D015151:Immunoblotting; D017370:Interleukin-11 / Q000494:pharmacology*; D007413:Intestinal Mucosa / Q000166:cytology* / Q000187:drug effects*; D020930:MAP Kinase Kinase Kinases / Q000037:antagonists & inhibitors / Q000502:physiology*; D008928:Mitochondria / Q000378:metabolism; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000037:antagonists & inhibitors / Q000502:physiology*; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000502:physiology*
chemical_list: D061945:Caspase Inhibitors; D004791:Enzyme Inhibitors; D053222:Fas Ligand Protein; D017370:Interleukin-11; D011065:Poly(ADP-ribose) Polymerases; D051057:Proto-Oncogene Proteins c-akt; D020930:MAP Kinase Kinase Kinases; D053148:Caspase 3; D053453:Caspase 9