title: Defective activation of ERK in macrophages lacking the p50/p105 subunit of NF-kappaB is responsible for elevated expression of IL-12 p40 observed after challenge with Helicobacter hepaticus.
abstract: Helicobacter hepaticus is an enterohepatic Helicobacter species that induces lower bowel inflammation in susceptible mouse strains, including those lacking the p50/p105 subunit of NF-kappaB. H. hepaticus-induced colitis is associated with elevated levels of IL-12 p40 expression, and p50/p105-deficient macrophages express higher levels of IL-12 p40 than wild-type macrophages after challenge with H. hepaticus. However, the molecular mechanisms by which the p50/p105 subunit of NF-kappaB suppresses IL-12 p40 expression have not yet been elucidated. In this study we have demonstrated that H. hepaticus challenge of macrophages induces ERK activation, and this event plays a critical role in inhibiting the ability of H. hepaticus to induce IL-12 p40. Activation of ERK requires both p50/p105 and the MAPK kinase kinase, Tpl-2. Inhibition of the induction of IL-12 p40 by ERK was independent of c-Rel, a known positive regulator of IL-12 p40. Instead, it was linked to the induction of c-Fos, a known inhibitor of IL-12 p40 expression. These results suggest that H. hepaticus induces ERK activation by a pathway dependent upon Tpl-2 and p105, and that activation of ERK inhibits the expression of IL-12 p40 by inducing c-Fos. Thus, a defect in ERK activation could play a pivotal role in the superinduction of IL-12 p40 observed after challenge of macrophages lacking the p50/p105 subunit of NF-kappaB with H. hepaticus.
authors.affiliation: Immunology Research Division, Department of Pathology, Brigham and Women's Hospital, Boston, MA 02115, USA.
authors.forename: Michal F
authors.initials: MF
authors.lastname: Tomczak
authors.forename: Mihaela
authors.initials: M
authors.lastname: Gadjeva
authors.forename: Yan Yan
authors.initials: YY
authors.lastname: Wang
authors.forename: Ketorah
authors.initials: K
authors.lastname: Brown
authors.forename: Ioanna
authors.initials: I
authors.lastname: Maroulakou
authors.forename: Philip N
authors.initials: PN
authors.lastname: Tsichlis
authors.forename: Susan E
authors.initials: SE
authors.lastname: Erdman
authors.forename: James G
authors.initials: JG
authors.lastname: Fox
authors.forename: Bruce H
authors.initials: BH
authors.lastname: Horwitz
mesh_terms: D000818:Animals; D002070:Butadienes / Q000494:pharmacology; D004789:Enzyme Activation; D048049:Extracellular Signal-Regulated MAP Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D044923:Helicobacter hepaticus / Q000276:immunology / Q000472:pathogenicity*; D066298:In Vitro Techniques; D016753:Interleukin-10 / Q000096:biosynthesis / Q000172:deficiency / Q000235:genetics; D018664:Interleukin-12 / Q000096:biosynthesis*; D053762:Interleukin-12 Subunit p40; D020935:MAP Kinase Signaling System / Q000187:drug effects; D008264:Macrophages / Q000187:drug effects / Q000276:immunology* / Q000378:metabolism* / Q000382:microbiology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D052002:NF-kappa B p50 Subunit / Q000172:deficiency* / Q000235:genetics; D009570:Nitriles / Q000494:pharmacology; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D021122:Protein Subunits / Q000096:biosynthesis*; D016760:Proto-Oncogene Proteins c-fos / Q000096:biosynthesis
chemical_list: D002070:Butadienes; D053762:Interleukin-12 Subunit p40; D052002:NF-kappa B p50 Subunit; D009570:Nitriles; D047428:Protein Kinase Inhibitors; D021122:Protein Subunits; D016760:Proto-Oncogene Proteins c-fos; C113580:U 0126; D016753:Interleukin-10; D018664:Interleukin-12; D048049:Extracellular Signal-Regulated MAP Kinases