Transforming growth factor-beta (TGF-beta) activates cytosolic phospholipase A2alpha (cPLA2alpha)-mediated prostaglandin E2 (PGE)2/EP1 and peroxisome proliferator-activated receptor-gamma (PPAR-gamma)/Smad signaling pathways in human liver cancer cells. A novel mechanism for subversion of TGF-beta-induced mitoinhibition.
Transforming growth factor-beta (TGF-beta) potently inhibits the growth of human epithelial cells. However, neoplastic epithelial cells become resistant to TGF-beta-mediated mitoinhibition, and the mechanisms for this alteration during tumorigenesis are not fully understood. This study was designed to determine whether there is an association between the cytosolic phospholipase A2alpha (cPLA2alpha)-controlled eicosanoid metabolism and the growth response to TGF-beta in human liver cancer cells. TGF-beta treatment induced simultaneous Smad-mediated gene transcription and phosphorylation of cPLA2alpha. Whereas Smad activation inhibited tumor cell growth, phosphorylation of cPLA2 alpha promoted growth and counteracted Smad-mediated mitoinhibition. TGF-beta1 failed to prevent the growth of cells with high basal expression of cPLA2alpha, but inhibition of cPLA2 alpha, cyclooxygenase-2 (COX-2), or EP1 receptor restored mitoinhibition by TGF-beta1 in these cells. These results suggest that resistance of tumor cells to TGF-beta-mediated mitoinhibition involves activation of cPLA2alpha/COX-2/EP1 signaling. Furthermore, the TGF-beta1-induced Smad transcriptional activity and mitoinhibition were blocked by overexpression of cPLA2alpha or peroxisome proliferator-activated receptor-gamma (PPAR-gamma) but enhanced by depletion of cPLA2alpha or PPAR-gamma. These findings, along with the observations that cPLA2alpha activates PPAR-gamma and that PPAR-gamma binds Smad3, illustrate novel cPLA2alpha/COX-2/EP1 and cPLA2alpha/PPAR-gamma/Smad signaling pathways that counteract the mitoinhibition by TGF-beta in human cancer cells.
Han
Chang
C
Department of Pathology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15213, USA.
Demetris
A Jake
AJ
Liu
Youhua
Y
Shelhamer
James H
JH
Wu
Tong
T
D002455:Cell Division; D002460:Cell Line; D045744:Cell Line, Tumor; D051546:Cyclooxygenase 2; D003600:Cytosol / Q000201:enzymology*; D004268:DNA-Binding Proteins / Q000378:metabolism; D015232:Dinoprostone / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D015777:Eicosanoids / Q000378:metabolism; D004789:Enzyme Activation; D017930:Genes, Reporter; D054513:Group IV Phospholipases A2; D006801:Humans; D015151:Immunoblotting; D007527:Isoenzymes / Q000378:metabolism; D008099:Liver / Q000378:metabolism; D008113:Liver Neoplasms / Q000378:metabolism*; D008156:Luciferases / Q000378:metabolism; D008565:Membrane Proteins; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D008954:Models, Biological; D016376:Oligonucleotides, Antisense / Q000737:chemistry; D047495:PPAR gamma / Q000378:metabolism*; D010741:Phospholipases A / Q000378:metabolism*; D010766:Phosphorylation; D010957:Plasmids / Q000378:metabolism; D011451:Prostaglandin-Endoperoxide Synthases / Q000378:metabolism; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000378:metabolism; D018078:Receptors, Prostaglandin E / Q000378:metabolism; D058306:Receptors, Prostaglandin E, EP1 Subtype; D015398:Signal Transduction; D051899:Smad2 Protein; D013997:Time Factors; D015534:Trans-Activators / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism; D014162:Transfection; D016212:Transforming Growth Factor beta / Q000378:metabolism*; D053773:Transforming Growth Factor beta1; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
D004268:DNA-Binding Proteins; D015777:Eicosanoids; D007527:Isoenzymes; D008565:Membrane Proteins; D016376:Oligonucleotides, Antisense; D047495:PPAR gamma; C545635:PTGER1 protein, human; D034741:RNA, Small Interfering; D018078:Receptors, Prostaglandin E; D058306:Receptors, Prostaglandin E, EP1 Subtype; C497782:SMAD2 protein, human; D051899:Smad2 Protein; C508960:TGFB1 protein, human; D015534:Trans-Activators; D014157:Transcription Factors; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; D008156:Luciferases; D051546:Cyclooxygenase 2; C496540:PTGS2 protein, human; D011451:Prostaglandin-Endoperoxide Synthases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D048051:p38 Mitogen-Activated Protein Kinases; D010741:Phospholipases A; D054513:Group IV Phospholipases A2; D015232:Dinoprostone