title: ERK pathway mediates P2X7 expression and cell death in renal interstitial fibroblasts exposed to necrotic renal epithelial cells.
abstract: We recently reported that necrotic renal proximal epithelial cells (RPTC) stimulate the expression of P2X7 receptor in renal fibroblasts and that P2X7 receptor mediates deleterious epithelial-fibroblast cross talk. The present study was carried out to investigate the signaling mechanism of necrotic RPTC-induced P2X7 expression in cultured renal interstitial fibroblasts (NRK-49F). Exposure of NRK-49F to necrotic RPTC supernatant (RPTC-Sup) induced a time- and dose-dependent phosphorylation of several signaling pathways including extracellular signal-regulated kinases (ERK1/2), p38, c-Jun N-terminal kinases (JNKs), and AKT in NRK-49F. Pharmacological inhibition of ERK1/2, but not p38, JNK, and AKT pathways, blocked RPTC-Sup-induced P2X7 expression and renal interstitial fibroblast death. Knockdown of ERK1/2 or MEK1, a direct upstream activator of ERK1/2, also reduced RPTC-Sup-induced P2X7 expression and cell death of renal fibroblasts. Conversely, overexpression of MEK1 enhanced these responses. Upon necrotic RPTC exposure, phosphorylation of Elk1, a transcriptional factor targeted by ERK1/2, was increased in NRK-49F, and knockdown of Elk1 by siRNA remarkably reduced RPTC-Sup-induced P2X7 expression as well as renal fibroblast death. Furthermore, silencing of MEK1 inhibited Elk1 phosphorylation in response to necrotic RPTC, whereas overexpression of MEK1 increased Elk1 phosphorylation. Taken together, these data reveal that necrotic RPTC induces P2X7 expression in renal fibroblasts through activation of the MEK1-ERK1/2-Elk1 signaling pathway.
authors.affiliation: Department of Medicine, Rhode Island Hospital, Warren Alpert Medical School of Brown University, Providence, USA.
authors.forename: Murugavel
authors.initials: M
authors.lastname: Ponnusamy
authors.forename: Na
authors.initials: N
authors.lastname: Liu
authors.forename: Rujun
authors.initials: R
authors.lastname: Gong
authors.forename: Haidong
authors.initials: H
authors.lastname: Yan
authors.forename: Shougang
authors.initials: S
authors.lastname: Zhuang
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D002450:Cell Communication / Q000502:physiology*; D002460:Cell Line; D004847:Epithelial Cells / Q000378:metabolism / Q000473:pathology*; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism*; D005347:Fibroblasts / Q000378:metabolism / Q000473:pathology*; D007673:Kidney Cortex Necrosis / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D007687:Kidney Tubules, Proximal / Q000378:metabolism / Q000473:pathology* / Q000503:physiopathology; D048369:MAP Kinase Kinase 1 / Q000037:antagonists & inhibitors / Q000378:metabolism; D048670:MAP Kinase Kinase 4 / Q000378:metabolism; D051379:Mice; D023421:Models, Animal; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D034741:RNA, Small Interfering / Q000494:pharmacology; D051381:Rats; D058486:Receptors, Purinergic P2X7 / Q000187:drug effects / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*; D050807:ets-Domain Protein Elk-1 / Q000378:metabolism; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
chemical_list: C494114:Elk1 protein, rat; D034741:RNA, Small Interfering; D058486:Receptors, Purinergic P2X7; D050807:ets-Domain Protein Elk-1; D051057:Proto-Oncogene Proteins c-akt; D048049:Extracellular Signal-Regulated MAP Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D048369:MAP Kinase Kinase 1; D048670:MAP Kinase Kinase 4