title: Anti-citrullinated protein antibodies activated ERK1/2 and JNK mitogen-activated protein kinases via binding to surface-expressed citrullinated GRP78 on mononuclear cells.
abstract: In a previous study, we found that anti-citrullinated protein antibodies (ACPAs) enhance nuclear factor (NF)-κB activity and tumor necrosis factor (TNF)-α production by normal human peripheral blood mononuclear cells (PBMCs) and U937 cells via binding to surface-expressed citrullinated glucose-regulated protein 78 (cit-GRP78). However, the downstream signaling pathways remain unclear after binding. In the present study, we firstly measured the effects of different kinase inhibitors on ACPA-mediated TNF-α production from normal PBMCs and monocytes. Then, the native and phosphorylated mitogen-activated protein kinases (MAPKs) were detected in ACPA-activated U937 cells by Western blotting. We also explored the role of the phosphoinositide 3-kinase (PI3K)-Akt pathway in activating IκB kinase alpha (IKK-α) in ACPA-stimulated U937 cells. Finally, we measured the amount of cit-GRP78 from PBMC membrane extracts in RA patients and controls. We found that MAPK and Akt inhibitors, but not PI3K inhibitor, remarkably suppressed ACPA-mediated TNF-α production. Interestingly, ACPAs selectively activated extracellular signal-regulated kinase 1/2 (ERK1/2) and c-jun N-terminal kinase (JNK), but not p38 MAPK, in U937 cells. This activation was suppressed by cit-GRP78, but not GRP78. The JNK activation further enhanced the phosphorylation of Akt and IKK-α. The expression of cit-GRP78 on cell membrane was higher in RA than normal PBMCs. Taken together; these results suggest that through binding to surface, over-expressed cit-GRP78 on RA PBMCs, ACPAs selectively activate ERK1/2 and JNK signaling pathways to enhance IKK-α phosphorylation, which leads to the activation of NF-κB and the production of TNF-α .
authors.affiliation: Division of Allergy, Immunology and Rheumatology, Buddhist Dalin Tzu Chi General Hospital, Chia-Yi, Taiwan.
authors.forename: Ming-Chi
authors.initials: MC
authors.lastname: Lu
authors.forename: Ning-Sheng
authors.initials: NS
authors.lastname: Lai
authors.forename: Wen-Yao
authors.initials: WY
authors.lastname: Yin
authors.forename: Hui-Chun
authors.initials: HC
authors.lastname: Yu
authors.forename: Hsien-Bin
authors.initials: HB
authors.lastname: Huang
authors.forename: Chien-Hsueh
authors.initials: CH
authors.lastname: Tung
authors.forename: Kuang-Yung
authors.initials: KY
authors.lastname: Huang
authors.forename: Chia-Li
authors.initials: CL
authors.lastname: Yu
mesh_terms: D000906:Antibodies / Q000276:immunology / Q000378:metabolism / Q000494:pharmacology*; D001172:Arthritis, Rheumatoid / Q000276:immunology / Q000378:metabolism; D016022:Case-Control Studies; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D000091342:Endoplasmic Reticulum Chaperone BiP; D004789:Enzyme Activation / Q000187:drug effects; D006360:Heat-Shock Proteins / Q000378:metabolism*; D006801:Humans; D051550:I-kappa B Kinase / Q000378:metabolism; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism*; D007963:Leukocytes, Mononuclear / Q000187:drug effects* / Q000378:metabolism*; D020935:MAP Kinase Signaling System / Q000187:drug effects; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D011485:Protein Binding; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000096:biosynthesis; D020298:U937 Cells
chemical_list: D000906:Antibodies; D000091342:Endoplasmic Reticulum Chaperone BiP; C000717247:HSPA5 protein, human; D006360:Heat-Shock Proteins; D047428:Protein Kinase Inhibitors; D014409:Tumor Necrosis Factor-alpha; D051057:Proto-Oncogene Proteins c-akt; D051550:I-kappa B Kinase; D048031:JNK Mitogen-Activated Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3