title: Characterization of cadmium chloride-induced BiP accumulation in Xenopus laevis A6 kidney epithelial cells.
abstract: Endoplasmic reticulum (ER) stress can result in the accumulation of unfolded/misfolded protein in the ER lumen, which can trigger the unfolded protein response (UPR) resulting in the activation of various genes including immunoglobulin-binding protein (BiP; also known as glucose-regulated protein 78 or HSPA5). BiP, an ER heat shock protein 70 (HSP70) family member, binds to unfolded protein, inhibits their aggregation and re-folds them in an ATP-dependent manner. While cadmium, an environmental contaminant, was shown to induce the accumulation of HSP70 in vertebrate cells, less information is available regarding the effect of this metal on BiP accumulation or function. In this study, cadmium chloride treatment of Xenopus laevis A6 kidney epithelial cells induced a dose- and time-dependent increase in BiP, HSP70 and heme oxygenase-1 (HO-1) accumulation. Exposure of cells to a relatively low cadmium concentration at a mild heat shock temperature of 30°C greatly enhanced BiP and HSP70 accumulation compared to cadmium at 22°C. Treatment of cells with the glutathione synthesis inhibitor, buthionine sulfoximine, enhanced cadmium-induced BiP and HSP70 accumulation. Immunocytochemistry revealed that cadmium-induced BiP accumulation occurred in a punctate pattern in the perinuclear region. In some cells treated with cadmium chloride or the proteasomal inhibitor, MG132, large BiP complexes were observed that co-localized with aggregated protein or aggresome-like structures. These BiP/aggresome-like structures were also observed in cells treated simultaneously with cadmium at 30°C or in the presence of buthionine sulfoximine. In amphibians, the association of BiP with unfolded protein and its possible role in aggresome function may be vital in the maintenance of cellular proteostasis.
authors.affiliation: Department of Biology, University of Waterloo, Waterloo, ON N2L 3G1, Canada.
authors.forename: Cody S
authors.initials: CS
authors.lastname: Shirriff
authors.affiliation: Department of Biology, University of Waterloo, Waterloo, ON N2L 3G1, Canada. Electronic address: heikkila@uwaterloo.ca.
authors.forename: John J
authors.initials: JJ
authors.lastname: Heikkila
mesh_terms: D000818:Animals; D019328:Buthionine Sulfoximine / Q000494:pharmacology; D019256:Cadmium Chloride / Q000633:toxicity*; D000001:Calcimycin / Q000494:pharmacology; D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D000091342:Endoplasmic Reticulum Chaperone BiP; D004785:Environmental Pollutants / Q000633:toxicity*; D004847:Epithelial Cells / Q000187:drug effects* / Q000378:metabolism; D005721:Glutamate-Cysteine Ligase / Q000037:antagonists & inhibitors / Q000378:metabolism; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D006360:Heat-Shock Proteins / Q000378:metabolism*; D018869:Heat-Shock Response; D051547:Heme Oxygenase-1 / Q000378:metabolism; D007668:Kidney / Q000187:drug effects* / Q000378:metabolism; D007976:Leupeptins / Q000494:pharmacology; D018384:Oxidative Stress; D061988:Proteasome Inhibitors / Q000494:pharmacology; D013997:Time Factors; D014415:Tunicamycin / Q000494:pharmacology; D056811:Unfolded Protein Response; D015854:Up-Regulation; D029867:Xenopus Proteins / Q000378:metabolism*; D014982:Xenopus laevis / Q000378:metabolism*
chemical_list: D000091342:Endoplasmic Reticulum Chaperone BiP; D004785:Environmental Pollutants; D018840:HSP70 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D007976:Leupeptins; D061988:Proteasome Inhibitors; D029867:Xenopus Proteins; D014415:Tunicamycin; D000001:Calcimycin; D019328:Buthionine Sulfoximine; D051547:Heme Oxygenase-1; D005721:Glutamate-Cysteine Ligase; D019256:Cadmium Chloride; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde
keywords: Aggregated protein; Aggresomes; Buthionine sulfoximine; GRP78; HO-1; HSP70; Heat shock; Unfolded protein response