Anti-citrullinated Protein Antibodies Activated ERK1/2 and JNK Mitogen-activated Protein Kinases via Binding to Surface-expressed Citrullinated GRP78 on Mononuclear Cells

• Published in: Journal of clinical immunology 2013-04, Vol.33 (3), p.558-566
• Main Authors: Lu, Ming-Chi, Lai, Ning-Sheng, Yin, Wen-Yao, Yu, Hui-Chun, Huang, Hsien-Bin, Tung, Chien-Hsueh, Huang, Kuang-Yung, Yu, Chia-Li
• Format: Article
• Language: English
• Subjects: 1-Phosphatidylinositol 3-kinase; AKT protein; Antibodies; Antibodies - immunology; Antibodies - metabolism; Antibodies - pharmacology; Arthritis, Rheumatoid - immunology; Arthritis, Rheumatoid - metabolism; Biomedical and Life Sciences; Biomedicine; c-Jun amino-terminal kinase; Case-Control Studies; Cell Membrane - metabolism; Cell membranes; Cells, Cultured; citrulline; Enzyme Activation - drug effects; Extracellular signal-regulated kinase; Heat-Shock Proteins - metabolism; Humans; I Kappa B kinase; I-kappa B Kinase - metabolism; Immunology; Infectious Diseases; Internal Medicine; JNK Mitogen-Activated Protein Kinases - metabolism; Leukocytes (mononuclear); Leukocytes, Mononuclear - drug effects; Leukocytes, Mononuclear - metabolism; MAP kinase; MAP Kinase Signaling System - drug effects; Medical Microbiology; Mitogen-Activated Protein Kinase 1 - metabolism; Mitogen-Activated Protein Kinase 3 - metabolism; Monocytes; NF- Kappa B protein; Original Research; Peripheral blood mononuclear cells; phosphoinositides; Phosphorylation; Phosphorylation - drug effects; Protein Binding; Protein Kinase Inhibitors - pharmacology; Proto-Oncogene Proteins c-akt - metabolism; Signal transduction; Tumor necrosis factor- alpha; Tumor Necrosis Factor-alpha - biosynthesis; U937 Cells; Western blotting
• ISSN: 0271-9142; 1573-2592
• DOI: 10.1007/s10875-012-9841-6

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 .