LPA-induced suppression of periostin in human osteosarcoma cells is mediated by the LPA(1)/Egr-1 axis.
Lysophosphatidic acid (LPA), a naturally occurring bioactive phospholipid, mediates a multitude of (patho)physiological events including activation of mitogen-activated protein kinases (MAPKs). As LPA may induce cellular reponses in human osteosarcoma, the present study aimed at investigating expression of various LPA receptors, LPA-mediated activation of MAPK via G-protein coupling, and expression of early response genes in a cellular model for human osteosarcoma. We show that MG-63 cells express three members of the endothelial differentiation gene (Edg) family of G-protein coupled receptor transcripts (LPA(1-3)) but only two (LPA(4/5)) out of three members of the non-Edg family LPA receptor transcripts. Stimulation of MG-63 cells with LPA or synthetic LPA receptor agonists resulted in p42/44 MAPK phosphorylation via LPA(1)-LPA(3) receptors. Using pharmacological inhibitors, we show that LPA-mediated phosphorylation of p42/44 MAPK by LPA receptor engagement is transmitted by G(αi)-dependent pathways through the Src family of tyrosine kinases. As a consequence, a rapid and transient upregulation of the zinc finger transcription factor early growth response-1 (Egr-1) was observed. Egr-1 expression was strictly mediated via G(αi)/Src/p42/44 MAPK pathway; no involvement of the G(αq/11)/PLC/PKC or the PLD/PI3 kinase/Akt pathways was found. LPA-induced expression of functional Egr-1 in MG-63 cells could be confirmed by electrophoretic mobility shift assay. LPA-induced Egr-1 upregulation was accompanied by a time-dependent decrease of periostin (previously called osteoblast-specific factor 2), a cell adhesion protein for pre-osteoblasts. Silencing of LPA(1) and/or Egr-1 in MG-63 cells reversed LPA-mediated suppression of periostin. We here demonstrate a crosslink between Egr-1 and periostin in cancer cells, in particular in human osteosarcoma.
Medical University of Graz, University Clinic of Pediatrics and Adolescent Medicine, Research Unit of Osteological Research and Analytical Mass Spectrometry, Auenbruggerplatz 30, A-8036 Graz, Austria. werner.windischhofer@medunigraz.at
Werner
W
Windischhofer
Evelyn
E
Huber
Christine
C
Rossmann
Michaela
M
Semlitsch
Kerstin
K
Kitz
Anamaria
A
Rauh
Trevor
T
Devaney
Hans-Jörg
HJ
Leis
Ernst
E
Malle
D015815:Cell Adhesion Molecules / Q000378:metabolism*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D004247:DNA / Q000378:metabolism; D051766:Early Growth Response Protein 1 / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D008246:Lysophospholipids / Q000494:pharmacology*; D020935:MAP Kinase Signaling System / Q000187:drug effects; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D012516:Osteosarcoma / Q000473:pathology*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D049368:Receptors, Lysophosphatidic Acid / Q000378:metabolism*
D015815:Cell Adhesion Molecules; C497325:EGR1 protein, human; D051766:Early Growth Response Protein 1; D008246:Lysophospholipids; C512835:POSTN protein, human; D012333:RNA, Messenger; D049368:Receptors, Lysophosphatidic Acid; D004247:DNA; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; C032881:lysophosphatidic acid