title: Tributyltin-induced endoplasmic reticulum stress and its Ca(2+)-mediated mechanism.
abstract: Organotin compounds, especially tributyltin chloride (TBT), have been widely used in antifouling paints for marine vessels, but exhibit various toxicities in mammals. The endoplasmic reticulum (ER) is a multifunctional organelle that controls post-translational modification and intracellular Ca(2+) signaling. When the capacity of the quality control system of ER is exceeded under stress including ER Ca(2+) homeostasis disruption, ER functions are impaired and unfolded proteins are accumulated in ER lumen, which is called ER stress. Here, we examined whether TBT causes ER stress in human neuroblastoma SH-SY5Y cells. We found that 700nM TBT induced ER stress markers such as CHOP, GRP78, spliced XBP1 mRNA and phosphorylated eIF2α. TBT also decreased the cell viability both concentration- and time-dependently. Dibutyltin and monobutyltin did not induce ER stress markers. We hypothesized that TBT induces ER stress via Ca(2+) depletion, and to test this idea, we examined the effect of TBT on intracellular Ca(2+) concentration using fura-2 AM, a Ca(2+) fluorescent probe. TBT increased intracellular Ca(2+) concentration in a TBT-concentration-dependent manner, and Ca(2+) increase in 700nM TBT was mainly blocked by 50μM dantrolene, a ryanodine receptor antagonist (about 70% inhibition). Dantrolene also partially but significantly inhibited TBT-induced GRP78 expression and cell death. These results suggest that TBT increases intracellular Ca(2+) concentration by releasing Ca(2+) from ER, thereby causing ER stress.
authors.affiliation: Graduate School of Biomedical and Health Sciences, Hiroshima University, Hiroshima 734-8553, Japan.
authors.forename: Midori
authors.initials: M
authors.lastname: Isomura
authors.forename: Yaichiro
authors.initials: Y
authors.lastname: Kotake
authors.forename: Kyoichi
authors.initials: K
authors.lastname: Masuda
authors.forename: Masatsugu
authors.initials: M
authors.lastname: Miyara
authors.forename: Katsuhiro
authors.initials: K
authors.lastname: Okuda
authors.forename: Shigeyoshi
authors.initials: S
authors.lastname: Samizo
authors.forename: Seigo
authors.initials: S
authors.lastname: Sanoh
authors.forename: Toru
authors.initials: T
authors.lastname: Hosoi
authors.forename: Koichiro
authors.initials: K
authors.lastname: Ozawa
authors.forename: Shigeru
authors.initials: S
authors.lastname: Ohta
mesh_terms: D015153:Blotting, Western; D002118:Calcium / Q000502:physiology*; D020013:Calcium Signaling / Q000187:drug effects; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D004268:DNA-Binding Proteins / Q000378:metabolism; D003620:Dantrolene / Q000494:pharmacology; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism; D000091342:Endoplasmic Reticulum Chaperone BiP; D059865:Endoplasmic Reticulum Stress / Q000187:drug effects*; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases / Q000378:metabolism; D006801:Humans; D046228:Microarray Analysis; D009125:Muscle Relaxants, Central / Q000494:pharmacology; D016133:Polymerase Chain Reaction; D000071701:Regulatory Factor X Transcription Factors; D014157:Transcription Factors / Q000378:metabolism; D014220:Trialkyltin Compounds / Q000633:toxicity*; D000071717:X-Box Binding Protein 1
chemical_list: D004268:DNA-Binding Proteins; D000091342:Endoplasmic Reticulum Chaperone BiP; C000717247:HSPA5 protein, human; D009125:Muscle Relaxants, Central; D000071701:Regulatory Factor X Transcription Factors; D014157:Transcription Factors; D014220:Trialkyltin Compounds; D000071717:X-Box Binding Protein 1; C000605543:XBP1 protein, human; C011559:tributyltin; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases; D003620:Dantrolene; D002118:Calcium
keywords: 2-(4-iodophenyl)-3-(4-nitrophenyl)-5-(2,4-disulfophenyl)-2H-tetrazolium; 4′,6-diamidino-2-phenylindole dihydrochloride; BSA; CCCP; CHOP; Calcium; DAPI; DBT; DMEM; Dulbecco's modified Eagle's medium; EDTA; ER; ER-associated degradation; ERAD; Endoplasmic reticulum stress; Fura-2 AM; GAPDH; GRP78; GRP94; HBSS; HEPES-buffered salt solution; IP(3); MBT; Organotin; PBS; PBST; ROS; SERCA; TBT; TBTO; UPR; VDCC; WST-1; XBP1; bis(tri-n-butyltin) oxide; bovine serum albumin; c/EBP homologous protein; carbonyl cyanide m-chlorophenylhydrazone; dibutyltin; eIF2; endoplasmic reticulum; ethylenediaminetetraacetic acid; eukaryotic initiation factor 2; fura-2 acetoxymethylester; glucose-regulated protein 78kDa; glucose-regulated protein 94kDa; glycelaldehyde-3-phosphate dehydrogenase; inositol 1,4,5-triphosphate; monobutyltin; phosphate-buffered saline; phosphate-buffered saline containing Tween 20; reactive oxygen species; sarco/endoplasmic reticulum Ca(2+)-ATPase; tributyltin; unfolded protein response; voltage-dependent Ca(2+) channel; x-box binding protein 1