title: Role of endoplasmic reticulum stress in epithelial-mesenchymal transition of alveolar epithelial cells: effects of misfolded surfactant protein.
abstract: Endoplasmic reticulum (ER) stress has been implicated in alveolar epithelial type II (AT2) cell apoptosis in idiopathic pulmonary fibrosis. We hypothesized that ER stress (either chemically induced or due to accumulation of misfolded proteins) is also associated with epithelial-mesenchymal transition (EMT) in alveolar epithelial cells (AECs). ER stress inducers, thapsigargin (TG) or tunicamycin (TN), increased expression of ER chaperone, Grp78, and spliced X-box binding protein 1, decreased epithelial markers, E-cadherin and zonula occludens-1 (ZO-1), increased the myofibroblast marker, α-smooth muscle actin (α-SMA), and induced fibroblast-like morphology in both primary AECs and the AT2 cell line, RLE-6TN, consistent with EMT. Overexpression of the surfactant protein (SP)-C BRICHOS mutant SP-C(ΔExon4) in A549 cells increased Grp78 and α-SMA and disrupted ZO-1 distribution, and, in primary AECs, SP-C(ΔExon4) induced fibroblastic-like morphology, decreased ZO-1 and E-cadherin and increased α-SMA, mechanistically linking ER stress associated with mutant SP to fibrosis through EMT. Whereas EMT was evident at lower concentrations of TG or TN, higher concentrations caused apoptosis. The Src inhibitor, 4-amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4]pyramidine) (PP2), abrogated EMT associated with TN or TG in primary AECs, whereas overexpression of SP-C(ΔExon4) increased Src phosphorylation, suggesting a common mechanism. Furthermore, increased Grp78 immunoreactivity was observed in AT2 cells of mice after bleomycin injury, supporting a role for ER stress in epithelial abnormalities in fibrosis in vivo. These results demonstrate that ER stress induces EMT in AECs, at least in part through Src-dependent pathways, suggesting a novel role for ER stress in fibroblast accumulation in pulmonary fibrosis.
authors.affiliation: Will Rogers Institute Pulmonary Research Center, Division of Pulmonary and Critical Care Medicine, Department of Medicine, University of Southern California, Keck School of Medicine, Los Angeles, CA 90033, USA.
authors.forename: Qian
authors.initials: Q
authors.lastname: Zhong
authors.forename: Beiyun
authors.initials: B
authors.lastname: Zhou
authors.forename: David K
authors.initials: DK
authors.lastname: Ann
authors.forename: Parviz
authors.initials: P
authors.lastname: Minoo
authors.forename: Yixin
authors.initials: Y
authors.lastname: Liu
authors.forename: Agnes
authors.initials: A
authors.lastname: Banfalvi
authors.forename: Manda S
authors.initials: MS
authors.lastname: Krishnaveni
authors.forename: Mickael
authors.initials: M
authors.lastname: Dubourd
authors.forename: Lucas
authors.initials: L
authors.lastname: Demaio
authors.forename: Brigham C
authors.initials: BC
authors.lastname: Willis
authors.forename: Kwang-Jin
authors.initials: KJ
authors.lastname: Kim
authors.forename: Roland M
authors.initials: RM
authors.lastname: duBois
authors.forename: Edward D
authors.initials: ED
authors.lastname: Crandall
authors.forename: Michael F
authors.initials: MF
authors.lastname: Beers
authors.forename: Zea
authors.initials: Z
authors.lastname: Borok
mesh_terms: D000818:Animals; D017209:Apoptosis; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D000091342:Endoplasmic Reticulum Chaperone BiP; D004848:Epithelium / Q000473:pathology*; D005347:Fibroblasts / Q000378:metabolism; D005786:Gene Expression Regulation; D006801:Humans; D008297:Male; D008648:Mesoderm / Q000473:pathology*; D051379:Mice; D009154:Mutation; D011489:Protein Denaturation; D011650:Pulmonary Alveoli / Q000378:metabolism*; D011658:Pulmonary Fibrosis / Q000378:metabolism; D037721:Pulmonary Surfactant-Associated Protein C / Q000737:chemistry*; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D000091342:Endoplasmic Reticulum Chaperone BiP; C000717247:HSPA5 protein, human; C000717248:Hspa5 protein, mouse; D037721:Pulmonary Surfactant-Associated Protein C