Mechanism of amyloid peptide induced CCR5 expression in monocytes and its inhibition by siRNA for Egr-1.
In Alzheimer's disease (AD), one finds increased presence of monocytes/macrophages and activated microglial cells in the brain. Immunohistochemical studies show increased expression of chemokine receptor 5 (CCR5) on reactive microglia associated with amyloid deposits in AD, suggesting that CCR5 may play a role in the regulation of the immune response in AD. In this study, we used peripheral blood monocytes and human monocytic THP-1 cell line as a model of microglia to delineate the cellular signaling mechanism of Abeta-induced CCR5 expression and the latter's role in the chemotaxis of monocytes. We observed that Abeta peptides at pathophysiological concentrations (125 nM) increased CCR5 mRNA and cell surface protein expression. The cellular signaling involved activation of c-Raf, ERK-1/ERK-2, and c-Jun NH(2)-terminal kinase. Analysis of some transcription factors associated with CCR5 promoter revealed that Abeta increased DNA binding activity of Egr-1 and AP-1. In addition, we show that CCR5 promoter contains an Egr-1 like consensus sequence GCGGGGGTG as demonstrated by 1) electrophoretic mobility shift assay, 2) transfection studies with truncated CCR5 gene promoter construct, and 3) chromatin immunoprecipitation analysis. Moreover, transfection of Egr-1 siRNA, but not of scrambled Egr-1 siRNA, in THP-1 cells resulted in >75% reduction in both Abeta-mediated CCR5 expression and concomitant chemotaxis to its ligands. We suggest that inhibition of Egr-1 by either Egr-1 siRNA or pharmacological agents may reduce activation of monocytes/microglia and possibly ameliorate the inflammation and progression of AD.
Giri
Ranjit K
RK
Department of Biochemistry & Molecular Biology, USC Keck School of Medicine, Los Angeles, CA 90033, USA.
Rajagopal
Vikram
V
Shahi
Shweta
S
Zlokovic
Berislav V
BV
Kalra
Vijay K
VK
D016229:Amyloid beta-Peptides / Q000378:metabolism*; D001483:Base Sequence; D002460:Cell Line; D002634:Chemotaxis, Leukocyte / Q000502:physiology; D047369:Chromatin Immunoprecipitation; D004277:DNA, Single-Stranded / Q000235:genetics*; D024202:Electrophoretic Mobility Shift Assay; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D005434:Flow Cytometry; D015870:Gene Expression; D005786:Gene Expression Regulation; D006801:Humans; D008954:Models, Biological; D008969:Molecular Sequence Data; D009000:Monocytes / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D034741:RNA, Small Interfering / Q000378:metabolism*; D019713:Receptors, CCR5 / Q000096:biosynthesis* / Q000235:genetics; D015398:Signal Transduction / Q000502:physiology*; D014162:Transfection; D048490:raf Kinases / Q000378:metabolism
D016229:Amyloid beta-Peptides; C400152:DNA enzyme ED5; D004277:DNA, Single-Stranded; D034741:RNA, Small Interfering; D019713:Receptors, CCR5; D048490:raf Kinases; D048049:Extracellular Signal-Regulated MAP Kinases