title: ATF6 pathway of unfolded protein response mediates advanced oxidation protein product-induced hypertrophy and epithelial-to-mesenchymal transition in HK-2 cells.
abstract: Advanced oxidation protein products (AOPPs) accelerate the progression of chronic kidney disease. We previously demonstrated that AOPPs induce hypertrophy and epithelial-to-mesenchymal transition (EMT) in human proximal tubular cells (HK-2 cells) through induction of endoplasmic reticulum (ER) stress. However, which pathway of unfolded protein response (UPR) induced by ER stress plays crucial roles in this process remains unclear. In this study, we investigated the roles of the protein kinase RNA-like ER kinase (PERK), activating transcription factor 6 (ATF6), and inositol-requiring enzyme 1 (IRE1) pathways of UPR in this process in HK-2 cells. AOPP treatment induced the overexpression of cleaved ATF6 and spliced form of X-box binding protein-1, and induced the phosphorylation of PERK, eukaryotic translation initiation factor 2α and IRE1. Furthermore, silencing of ATF6 increased E-cadherin and zonula occludens-1 expression, lowered the expression of vimentin, and downregulated total protein content, whereas knockdown of PERK or IRE1 resulted in no difference compared with the scramble siRNA-transfected cells. AOPP-induced phosphorylation of Src, which was reproduced by thapsigargin, an inducer of ER stress, was partly reversed by salubrinal, an inhibitor of ER stress. Furthermore, the Src inhibitor saracatinib effectively blocked AOPP-induced phosphorylation of Src, activation of ER stress, hypertrophy, and EMT in HK-2 cells. Collectively, our results indicate that AOPPs induce the PERK, ATF6, and IRE1 pathways of UPR, and the ATF6 pathway rather than the other two pathways mediates AOPP-induced HK-2-cell hypertrophy and EMT. We also suggest that the ER stress involved in this process is likely mediated by the activation of Src kinase.
authors.affiliation: Department of Nephrology, Zhujiang Hospital, Southern Medical University, No. 253, Gongye Road, Haizhu District, Guangzhou, 510280, Guangdong, China.
authors.forename: Xun
authors.initials: X
authors.lastname: Tang
authors.forename: Xiujie
authors.initials: X
authors.lastname: Liang
authors.forename: Minhui
authors.initials: M
authors.lastname: Li
authors.forename: Tingting
authors.initials: T
authors.lastname: Guo
authors.forename: Na
authors.initials: N
authors.lastname: Duan
authors.forename: Yue
authors.initials: Y
authors.lastname: Wang
authors.forename: Guang
authors.initials: G
authors.lastname: Rong
authors.forename: Lei
authors.initials: L
authors.lastname: Yang
authors.forename: Shaojie
authors.initials: S
authors.lastname: Zhang
authors.forename: Jun
authors.initials: J
authors.lastname: Zhang
mesh_terms: D051702:Activating Transcription Factor 6 / Q000378:metabolism*; D062107:Advanced Oxidation Protein Products / Q000494:pharmacology*; D049108:Cell Enlargement / Q000187:drug effects; D002460:Cell Line; D004722:Endoribonucleases / Q000378:metabolism; D058750:Epithelial-Mesenchymal Transition / Q000187:drug effects*; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D007687:Kidney Tubules, Proximal / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D056811:Unfolded Protein Response / Q000187:drug effects*; D019892:eIF-2 Kinase / Q000378:metabolism
chemical_list: C497111:ATF6 protein, human; D051702:Activating Transcription Factor 6; D062107:Advanced Oxidation Protein Products; C460640:EIF2AK3 protein, human; C528229:ERN1 protein, human; D017346:Protein Serine-Threonine Kinases; D019892:eIF-2 Kinase; D004722:Endoribonucleases