title: Modulation of albumin-induced endoplasmic reticulum stress in renal proximal tubule cells by upregulation of mapk phosphatase-1.
abstract: High amounts of albumin in urine cause tubulointerstitial damage that leads to a rapid deterioration of the renal function. Albumin exerts its injurious effects on renal cells through a process named endoplasmic reticulum (ER) stress due to the accumulation of unfolded proteins in the ER lumen. In addition, albumin promotes phosphorylation and consequent activation of MAPKs such as ERK1/2. Since ERK1/2 activation promoted by albumin is a transient event, the aims of the present work were to identify the phosphatase involved in their dephosphorylation in albumin-exposed cells and to analyze the putative regulation of this phosphatase by albumin. We also sought to determine the role played by the phospho/dephosphorylation of ERK1/2 in the cellular response to albumin-induced ER stress. MAP kinase phosphatase-1, MKP-1, is a nuclear enzyme involved in rapid MAPK dephosphorylation. Here we present evidence supporting the notion that this phosphatase is responsible for ERK1/2 dephosphorylation after albumin exposure in OK cells. Moreover, we demonstrate that exposure of OK cells to albumin transiently increases MKP-1 protein levels. The increase was evident after 15 min of exposure, peaked at 1 h (6-fold) and declined thereafter. In cells overexpressing flag-MKP-1, albumin caused the accumulation of this chimera, promoting MKP-1 stabilization by a posttranslational mechanism. Albumin also promoted a transient increase in MKP-1 mRNA levels (3-fold at 1 h) through the activation of gene transcription. In addition, we also show that albumin increased mRNA levels of GRP78, a key marker of ER stress, through an ERK-dependent pathway. In line with this finding, our studies demonstrate that flag-MKP-1 overexpression blunted albumin-induced GRP78 upregulation. Thus, our work demonstrates that albumin overload not only triggers MAPK activation but also tightly upregulates MKP-1 expression, which might modulate ER stress response to albumin overload.
authors.affiliation: Laboratory of Phosphatases in Signal Transduction, Institute for Biomedical Research (INBIOMED), Department of Biochemistry, School of Medicine, University of Buenos Aires, Buenos Aires, Argentina.
authors.forename: Alejandra
authors.initials: A
authors.lastname: Gorostizaga
authors.forename: Maria Mercedes
authors.initials: MM
authors.lastname: Mori Sequeiros García
authors.forename: Andrea
authors.initials: A
authors.lastname: Acquier
authors.forename: Natalia V
authors.initials: NV
authors.lastname: Gomez
authors.forename: Paula M
authors.initials: PM
authors.lastname: Maloberti
authors.forename: Carlos F
authors.initials: CF
authors.lastname: Mendez
authors.forename: Cristina
authors.initials: C
authors.lastname: Paz
mesh_terms: D000818:Animals; D002417:Cattle; D002478:Cells, Cultured; D048293:Didelphis / Q000378:metabolism*; D054638:Dual Specificity Phosphatase 1 / Q000235:genetics / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D007687:Kidney Tubules, Proximal / Q000166:cytology / Q000378:metabolism*; D018384:Oxidative Stress; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012710:Serum Albumin, Bovine / Q000378:metabolism*; D015854:Up-Regulation
chemical_list: D012710:Serum Albumin, Bovine; D054638:Dual Specificity Phosphatase 1
keywords: 2-amino-3-methoxyphenyl)4H-1-benzopyran-4-one; Act D; Albumin; Anthra[1-9-cd]pyrazol-6(2H); BSA; CHX; ER; ERK1/2; ERKs; Endoplasmic reticulum stress; Free fatty acid albumin; GRP78; JNKs; MAPK kinases; MAPK phosphatase; MAPKKs; MKP; MKPs; OK; OK cells; Opossum kidney; PD98059; SAPKs; SP600125; UPR; actinomycin D; c-Jun NH2-terminal protein kinases; cycloheximide; endoplasmic reticulum; extracellular signal-regulated kinases; glucose-regulated protein 78; stress-activated protein kinases; unfolded protein response