title: Angiotensin II-induced down-regulation of inositol trisphosphate receptors in WB rat liver epithelial cells. Evidence for involvement of the proteasome pathway.
abstract: Chronic stimulation of WB rat liver epithelial cells by angiotensin II (Ang II) resulted in the down-regulation of both type I and type III myo-inositol 1,4,5-trisphosphate receptors (IP3Rs). Stimulation with vasopressin, bradykinin, epidermal growth factor, or 12-O-tetradecanoylphorbol-13-acetate was without effect. Ang II-induced down-regulation of IP3Rs could be detected within 2 h and resulted in an inhibition of IP3-induced Ca2+ release from permeabilized cells. IP3R down-regulation was reversible, and both homo- and heterooligomers of IP3Rs were equally susceptible to Ang II-induced degradation. Chloroquine and NH4Cl increased the basal levels of IP3Rs by 2-fold, suggesting that the basal turnover of IP3Rs occurs via a lysosomal pathway. However, Ang II-induced degradation of IP3R was not affected by these inhibitors, suggesting that stimulated degradation of IP3Rs occurs via a non-lysosomal pathway. The cysteine protease and proteasomal inhibitor N-acetyl-Leu-Leu-norleucinal completely prevented Ang II-mediated down-regulation of IP3Rs, whereas the structural analog N-acetyl-Leu-Leu-methioninal was without effect. Lactacystin, a highly specific proteasome inhibitor, also blocked Ang II-mediated IP3R degradation. Stimulation with Ang II increased the amount of IP3R immunoprecipitated by anti-ubiquitin antibodies. We conclude that Ang II-stimulated IP3R degradation involves enhanced ubiquitination of the protein and degradation by the proteasome pathway.
authors.affiliation: Department of Pathology, Thomas Jefferson University School of Medicine, Philadelphia, Pennsylvania 19107, USA.
authors.forename: S
authors.initials: S
authors.lastname: Bokkala
authors.forename: S K
authors.initials: SK
authors.lastname: Joseph
mesh_terms: D000111:Acetylcysteine / Q000031:analogs & derivatives / Q000494:pharmacology; D000804:Angiotensin II / Q000494:pharmacology*; D000818:Animals; D015220:Calcium Channels / Q000378:metabolism*; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation / Q000187:drug effects*; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism*; D053496:Inositol 1,4,5-Trisphosphate Receptors; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D009097:Multienzyme Complexes / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex; D051381:Rats; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism*; D014452:Ubiquitins / Q000378:metabolism
chemical_list: D015220:Calcium Channels; D015853:Cysteine Proteinase Inhibitors; D053496:Inositol 1,4,5-Trisphosphate Receptors; D009097:Multienzyme Complexes; D018160:Receptors, Cytoplasmic and Nuclear; D014452:Ubiquitins; D000804:Angiotensin II; C067713:lactacystin; D015544:Inositol 1,4,5-Trisphosphate; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; D000111:Acetylcysteine