title: Sodium arsenite and cadmium chloride induction of proteasomal inhibition and HSP accumulation in Xenopus laevis A6 kidney epithelial cells.
abstract: Sodium arsenite (NA) and cadmium chloride (CdCl(2)) are relatively abundant environmental toxicants that have multiple toxic effects including carcinogenesis, dysfunction of gene regulation and DNA and protein damage. In the present study, treatment of Xenopus laevis A6 kidney epithelial cells with concentrations of NA (20-30 μM) or CdCl(2) (100-200 μM) that induced HSP30 and HSP70 accumulation also produced an increase in the relative levels of ubiquitinated protein. Actin protein levels were unchanged in these experiments. In time course experiments, the levels of ubiquitinated protein and HSPs increased over a 24h exposure to NA or CdCl(2). Furthermore, treatment of cells with NA or CdCl(2) reduced the relative levels of proteasome chymotrypsin (CT)-like activity compared to control. Interestingly, pretreatment of cells with the HSP accumulation inhibitor, KNK437, prior to NA or CdCl(2) exposure decreased the relative levels of ubiquitinated protein as well as HSP30 and HSP70. A similar finding was made with ubiquitinated protein induced by proteasomal inhibitors, MG132 and celastrol, known to induce HSP accumulation in A6 cells. However, the NA- or CdCl(2)-induced decrease in proteasome CT-like activity was not altered by KNK437 pretreatment. This study has shown for the first time in poikilothermic vertebrates that NA and CdCl(2) can inhibit proteasomal activity and that there is a possible association between HSP accumulation and the mechanism of protein ubiquitination.
authors: Department of Biology, University of Waterloo, Waterloo, ON, Canada N2L 3G1.
authors: Jara J
authors: JJ
authors: Brunt
authors: Saad
authors: S
authors: Khan
authors: John J
authors: JJ
authors: Heikkila
mesh_terms: D000818:Animals; D018053:Arsenites / Q000633:toxicity*; D001559:Benzhydryl Compounds / Q000494:pharmacology; D019256:Cadmium Chloride / Q000633:toxicity*; D002460:Cell Line; D002918:Chymotrypsin / Q000037:antagonists & inhibitors / Q000378:metabolism; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004785:Environmental Pollutants / Q000633:toxicity; D004847:Epithelial Cells / Q000187:drug effects* / Q000378:metabolism; D050890:HSP30 Heat-Shock Proteins / Q000378:metabolism; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D006360:Heat-Shock Proteins / Q000378:metabolism*; D015151:Immunoblotting; D007668:Kidney / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D007976:Leupeptins / Q000494:pharmacology; D053978:Pentacyclic Triterpenes; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D061988:Proteasome Inhibitors; D011760:Pyrrolidinones / Q000494:pharmacology; D017670:Sodium Compounds / Q000633:toxicity*; D013997:Time Factors; D014315:Triterpenes / Q000494:pharmacology; D057149:Ubiquitinated Proteins / Q000378:metabolism; D054875:Ubiquitination / Q000187:drug effects; D029867:Xenopus Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D014982:Xenopus laevis
chemical_list: D018053:Arsenites; D001559:Benzhydryl Compounds; D015853:Cysteine Proteinase Inhibitors; D004785:Environmental Pollutants; D050890:HSP30 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins; D006360:Heat-Shock Proteins; C410027:KNK 437; D007976:Leupeptins; D053978:Pentacyclic Triterpenes; D061988:Proteasome Inhibitors; D011760:Pyrrolidinones; D017670:Sodium Compounds; D014315:Triterpenes; D057149:Ubiquitinated Proteins; D029867:Xenopus Proteins; C017947:sodium arsenite; D002918:Chymotrypsin; D046988:Proteasome Endopeptidase Complex; D019256:Cadmium Chloride; C050414:celastrol; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde