Signaling mechanisms responsible for lysophosphatidic acid-induced urokinase plasminogen activator expression in ovarian cancer cells.
Lysophosphatidic acid (LPA) enhances urokinase plasminogen activator (uPA) expression in ovarian cancer cells; however, the molecular mechanisms responsible for this event have not been investigated. In this study, we used the invasive ovarian cancer SK-OV-3 cell line to explore the signaling molecules and pathways essential for LPA-induced uPA up-regulation. With the aid of specific inhibitors and dominant negative forms of signaling molecules, we determined that the G(i)-associated pathway mediates this LPA-induced event. Moreover, constitutively active H-Ras and Raf-1-activating H-Ras mutant enhance uPA expression, whereas dominant negative H-Ras and Raf-1 block LPA-induced uPA up-regulation, suggesting that the Ras-Raf pathway works downstream of G(i) to mediate this LPA-induced process. Surprisingly, dominant negative MEK1 or Erk2 displays only marginal inhibitory effect on LPA-induced uPA up-regulation, suggesting that a signaling pathway distinct from Raf-MEK1/2-Erk is the prominent pathway responsible for this process. In this report, we demonstrate that LPA activates NF-kappaB in a Ras-Raf-dependent manner and that blocking NF-kappaB activation with either non-phosphorylable IkappaB or dominant negative IkappaB kinase abolished LPA-induced uPA up-regulation and uPA promoter activation. Furthermore, introducing mutations to knock out the NF-kappaB binding site of the uPA promoter results in over 80% reduction in LPA-induced uPA promoter activation, whereas this activity is largely intact with the promoter containing mutations in the AP1 binding sites. Thus these results suggest that the G(i)-Ras-Raf-NF-kappaB signaling cascade is responsible for LPA-induced uPA up-regulation in ovarian cancer cells.
Li
Hongbin
H
Department of Immunology and Molecular Biology, The Scripps Research Institute, 10550 N. Torrey Pines Rd., La Jolla, California 92037, USA.
Ye
Xiaoqin
X
Mahanivong
Chitladda
C
Bian
Dafang
D
Chun
Jerold
J
Huang
Shuang
S
D000256:Adenoviridae / Q000235:genetics; D000818:Animals; D001665:Binding Sites; D045744:Cell Line, Tumor; D005260:Female; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic; D005799:Genes, Dominant; D006801:Humans; D008246:Lysophospholipids / Q000378:metabolism*; D009154:Mutation; D016328:NF-kappa B / Q000378:metabolism; D009361:Neoplasm Invasiveness; D010051:Ovarian Neoplasms / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D011956:Receptors, Cell Surface / Q000378:metabolism; D055293:Receptors, Urokinase Plasminogen Activator; D015398:Signal Transduction; D014162:Transfection; D015854:Up-Regulation; D014568:Urokinase-Type Plasminogen Activator / Q000096:biosynthesis*; D048490:raf Kinases / Q000378:metabolism; D018631:ras Proteins / Q000378:metabolism
D008246:Lysophospholipids; D016328:NF-kappa B; C524898:PLAUR protein, human; D011956:Receptors, Cell Surface; D055293:Receptors, Urokinase Plasminogen Activator; D048490:raf Kinases; D014568:Urokinase-Type Plasminogen Activator; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D018631:ras Proteins; C032881:lysophosphatidic acid