title: Limitation of individual folding resources in the ER leads to outcomes distinct from the unfolded protein response.
abstract: ER stress leads to upregulation of multiple folding and quality control components, known as the unfolded protein response (UPR). Glucose Regulated Protein 78 (GRP78) (also known as binding immunoglobulin protein, BiP, and HSPA5) and GRP94 are often upregulated coordinately as part of this homeostatic response. Given that endoplasmic reticulum (ER) chaperones have distinct sets of clients, we asked how cells respond to ablation of individual chaperones. The cellular responses to silencing BiP, GRP94, HSP47, PDIA6 and OS-9, were distinct. When BiP was silenced, a widespread UPR was observed, but when GRP94 was either inhibited or depleted by RNA interference (RNAi), the expression of only some genes was induced, notably those encoding BiP and protein disulfide isomerase A6 (PDIA6). Silencing of HSP47 or OS-9 did not lead to any compensatory induction of other genes. The selective response to GRP94 depletion was distinct from a typical ER stress response, both because other UPR target genes were not affected and because the canonical UPR signaling branches were not activated. The response to silencing of GRP94 did not preclude further UPR induction when chemical stress was imposed. Importantly, re-expression of wild-type GRP94 in the silenced cells prevented the upregulation of BiP and PDIA6, whereas re-expression of an ATPase-deficient GRP94 mutant did not, indicating that cells monitor the activity state of GRP94. These findings suggest that cells are able to distinguish among folding resources and generate distinct responses.
authors.affiliation: Department of Pathology and Laboratory Medicine, Children's Hospital of Philadelphia, PA 19104, USA.
authors.forename: Davide
authors.initials: D
authors.lastname: Eletto
authors.forename: Avinash
authors.initials: A
authors.lastname: Maganty
authors.forename: Daniela
authors.initials: D
authors.lastname: Eletto
authors.forename: Devin
authors.initials: D
authors.lastname: Dersh
authors.forename: Catherine
authors.initials: C
authors.lastname: Makarewich
authors.forename: Chhanda
authors.initials: C
authors.lastname: Biswas
authors.forename: James C
authors.initials: JC
authors.lastname: Paton
authors.forename: Adrienne W
authors.initials: AW
authors.lastname: Paton
authors.forename: Shirin
authors.initials: S
authors.lastname: Doroudgar
authors.forename: Christopher C
authors.initials: CC
authors.lastname: Glembotski
authors.forename: Yair
authors.initials: Y
authors.lastname: Argon
mesh_terms: D000818:Animals; D000091342:Endoplasmic Reticulum Chaperone BiP; D059865:Endoplasmic Reticulum Stress / Q000235:genetics; D020868:Gene Silencing; D006367:HeLa Cells; D006360:Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D041681:NIH 3T3 Cells; D019704:Protein Disulfide-Isomerases / Q000235:genetics / Q000378:metabolism; D017510:Protein Folding; D015398:Signal Transduction; D056811:Unfolded Protein Response / Q000235:genetics*
chemical_list: D000091342:Endoplasmic Reticulum Chaperone BiP; C000717247:HSPA5 protein, human; D006360:Heat-Shock Proteins; C000717248:Hspa5 protein, mouse; D008562:Membrane Glycoproteins; C053387:endoplasmin; C526507:Pdia6 protein, mouse; D019704:Protein Disulfide-Isomerases