title: Complement-mediated activation of calcium-independent phospholipase A2γ: role of protein kinases and phosphorylation.
abstract: In experimental membranous nephropathy, complement C5b-9-induces glomerular epithelial cell (GEC) injury and proteinuria. The effects of C5b-9 are mediated via signaling pathways, including calcium-independent phospholipase A(2)γ (iPLA(2)γ), and mitogen-activated protein kinases (MAPKs) such as extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and p38. The iPLA(2)γ pathway is cytoprotective. This study addresses the mechanisms of iPLA(2)γ activation. iPLA(2)γ activity was monitored by quantifying prostaglandin E(2) (PGE(2)) production. In GECs, iPLA(2)γ localized at the endoplasmic reticulum and mitochondria. Complement-mediated production of PGE(2) was amplified in GECs that overexpress iPLA(2)γ, compared with control cells, and was blocked by the iPLA(2)γ inhibitor bromoenol lactone in both iPLA(2)γ-overexpressing and control GECs. In GECs that overexpress iPLA(2)γ, complement-mediated PGE(2) production was reduced by inhibitors of MAP/ERK kinase 1 (MEK1) and p38 but not JNK. In COS-1 cells that overexpress iPLA(2)γ and cyclooxygenase-1, PGE(2) production was induced by co-expression of constitutively active MEK1 or MAPK-interacting kinase 1 (MNK1) as well as by stimulation with epidermal growth factor (EGF) + ionomycin. Complement- and EGF + ionomycin-stimulated iPLA(2)γ activity was attenuated by the S511A/S515A double mutation. Moreover, complement and EGF + ionomycin enhanced phosphorylation of Ser-511. Thus, complement-mediated activation of iPLA(2)γ is mediated via ERK and p38 pathways, and phosphorylation of Ser-511 and/or Ser-515 plays a key role in the catalytic activity and signaling of iPLA(2)γ. Defining the mechanisms by which complement activates iPLA(2)γ provides opportunities for development of novel therapeutic approaches to GEC injury and proteinuria.
authors.affiliation: Department of Medicine, McGill University Health Centre, McGill University, Montreal, Quebec H3A 1A1, Canada.
authors.forename: Hanan
authors.initials: H
authors.lastname: Elimam
authors.forename: Joan
authors.initials: J
authors.lastname: Papillon
authors.forename: Tomoko
authors.initials: T
authors.lastname: Takano
authors.forename: Andrey V
authors.initials: AV
authors.lastname: Cybulsky
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D019556:COS Cells; D061207:Calcium Ionophores / Q000494:pharmacology; D002460:Cell Line; D002522:Chlorocebus aethiops; D015938:Complement Membrane Attack Complex / Q000378:metabolism* / Q000494:pharmacology; D051545:Cyclooxygenase 1 / Q000235:genetics / Q000378:metabolism; D015232:Dinoprostone / Q000235:genetics / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000201:enzymology / Q000235:genetics; D004815:Epidermal Growth Factor / Q000494:pharmacology; D015433:Glomerulonephritis, Membranous / Q000201:enzymology* / Q000235:genetics / Q000473:pathology; D054522:Group VI Phospholipases A2 / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007155:Immunologic Factors / Q000378:metabolism / Q000494:pharmacology; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism; D015759:Ionomycin / Q000494:pharmacology; D007678:Kidney Glomerulus / Q000201:enzymology* / Q000293:injuries / Q000473:pathology; D048369:MAP Kinase Kinase 1 / Q000235:genetics / Q000378:metabolism; D020125:Mutation, Missense; D010766:Phosphorylation / Q000187:drug effects / Q000235:genetics; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D011507:Proteinuria / Q000201:enzymology / Q000235:genetics; D051381:Rats
chemical_list: D061207:Calcium Ionophores; D015938:Complement Membrane Attack Complex; D007155:Immunologic Factors; D047908:Intracellular Signaling Peptides and Proteins; D015759:Ionomycin; D004815:Epidermal Growth Factor; D051545:Cyclooxygenase 1; C496511:PTGS1 protein, human; C491395:MKNK1 protein, human; D017346:Protein Serine-Threonine Kinases; D048369:MAP Kinase Kinase 1; C482125:MAP2K1 protein, human; D054522:Group VI Phospholipases A2; D015232:Dinoprostone