title: Okadaic acid stimulates caspase-like activities and induces apoptosis of cultured rat mesangial cells.
abstract: Glomerular mesangial cells play an important role in the development of glomerulosclerosis. Mesangial cell apoptosis has been shown to be involved in different stages of development of glomerulonephritis. The aim of the present study was to evaluate the effect of inhibition of serine/threonine phosphatases by okadaic acid, a shell fish toxin, on rat mesangial cell apoptosis and to examine the molecular mechanisms particularly the role of caspases. Okadaic acid significantly induced mesangial cell apoptosis, as measured by an increase in cytoplasmic nucleosome-associated DNA fragmentation. The induction of apoptosis was dependent on protein synthesis, because cyclohexamide, a protein synthesis inhibitor, blocked okadaic acid-induced apoptosis. In addition, okadaic acid stimulated caspase activities (as measured by caspase substrate peptide hydrolysis) in cultured rat mesangial cells at different time points. After 12 h treatment, okadaic acid caused a modest increase in caspase-8 (IETD-pNAse) (159.3 +/- 6.7%) activity, while after 18 h treatment, okadaic acid caused a significant increase in caspase-3 (DEVD-pNAse) (906 +/- 245%) activity. Okadaic acid-stimulated caspase-3 activity was inhibited by Z-IETD-FMK (caspase-8 inhibitor) suggesting that the caspase-3 activity is downstream of caspase-8 activity. Both caspase-3 and caspase-8 inhibitors blocked okadaic acid-stimulated apoptosis. These data suggest that inhibition of protein phosphatases by okadaic acid induces apoptosis in rat mesangial cells by activating caspase-3- and -8-like activities and that caspase-3-like activity is downstream of caspase-8-like activity.
authors.affiliation: Department of Physiology, Michigan State University, East Lansing, MI, USA.
authors.forename: Narayanan
authors.initials: N
authors.lastname: Parameswaran
authors.forename: William S
authors.initials: WS
authors.lastname: Spielman
authors.forename: David P
authors.initials: DP
authors.lastname: Brooks
authors.forename: Ponnal
authors.initials: P
authors.lastname: Nambi
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D053148:Caspase 3; D053181:Caspase 8; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism*; D002478:Cells, Cultured; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D004797:Enzyme-Linked Immunosorbent Assay; D005920:Glomerular Mesangium / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D006868:Hydrolysis / Q000187:drug effects; D019319:Okadaic Acid / Q000494:pharmacology*; D009842:Oligopeptides / Q000494:pharmacology; D051381:Rats
chemical_list: D061945:Caspase Inhibitors; D015853:Cysteine Proteinase Inhibitors; D009842:Oligopeptides; C425644:isoleucyl-glutamyl-threonyl-aspartic acid fluoromethyl ketone; D019319:Okadaic Acid; C505410:Casp3 protein, rat; C505528:Casp8 protein, rat; D053148:Caspase 3; D053181:Caspase 8; D020169:Caspases