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Scientific Report 2005
Immunology
Lysophosphatidic
Acid–Induced Expression of Urokinase in Ovarian Cancer Cells
H.
Li, C. Mahanivong, D. Bian, S. Huang
Ascites fluid and plasma of patients with ovarian cancer have high concentrations of lysophosphatidic
acid (LPA). In experimental models, LPA promotes invasion and metastasis of ovarian
cancer cells by enhancing cell migration, upregulating expression of angiogenic
factors, and promoting cell survival and proliferation. Recently, we focused on
how LPA affects the expression of urokinase, an invasion-associated protease, in
ovarian cancer cells.
We found that LPA can upregulate expression of urokinase in the majority of ovarian cancer cell
lines but not in any normal ovary surface epithelial cells. Using an invasive ovarian
cancer cell line as a model system, we explored the signaling molecules and pathways
essential for LPA-induced upregulation of urokinase. Using specific inhibitors and
dominant-negative forms of signaling molecules, we found that the pathway associated
with the GTP-binding protein Gi, but not the pathways associated with
the GTP-binding proteins G12/13 and Gq, mediates this LPA-induced
event. Moreover, both constitutively active H-Ras (V12) and Raf-1 (BXB) enhanced
urokinase expression, whereas dominant-negative H-Ras (N17) and Raf-1 (301A) blocked
LPA-induced urokinase upregulation, suggesting that the Ras-Raf pathway works downstream
of Gi to mediate this LPA-induced process. Surprisingly, dominant-negative
MAP kinase kinase (MEK) 1 or extracellular signal–regulated kinase (ERK) 2
had only a marginal inhibitory effect on LPA-induced urokinase upregulation, suggesting
that a signaling pathway distinct from Raf-MEK1/2-ERK is the prominent pathway responsible
for this process.
In other studies, we showed that LPA activates the transcription factor NF-κB in a Ras-Raf–dependent manner and that blocking NF-κB activation with either nonphophorylable IκB or dominant-negative IKKβ
abolished LPA-induced upregulation of urokinase and activation of the urokinase promoter. Furthermore, introducing mutations to delete the NF-κB binding site of the urokinase promoter resulted in more than an 80% reduction in LPA-induced activation of the promoter. In contrast, LPA-induced activation of the promoter was only moderately affected by introducing mutations in the AP1 binding sites of the promoter. These results suggest that the Gi–Ras–Raf–NF-κB signaling cascade is responsible for LPA-induced upregulation of urokinase in ovarian cancer cells.
Publications
Chen, L.-Y., Doerner, A., Lehmann, P.F., Huang, S., Zhong, G., Pan, Z.K. A novel protein kinase C (PKCε)
is required for fMet-Leu-Phe-induced activation of NF-κB in human peripheral blood monocytes. J. Biol. Chem. 280:22497, 2005.
Jing, Q., Huang, S., Guth, S., Zarubin, T., Motoyama, A., Chen, J., Di Padova, F., Lin, S.-C., Gram, H., Han, J.
Involvement of microRNA in AU-rich element-mediated mRNA instability. Cell 120:623, 2005.
Li, H., Ye, X., Mahanivong, C., Bian, D., Chun, J., Huang, S. Signaling mechanisms responsible for lysophosphatidic acid-induced urokinase plasminogen activator expression in ovarian cancer cells. J .Biol. Chem. 280:10564, 2005.
Yu, J., Bian, D., Mahanivong, C., Chang, R.K., Zhou, W., Huang, S. p38 Mitogen-activated protein kinase regulation of endothelial cell migration depends on urokinase plasminogen activator expression. J. Biol. Chem. 279:50446, 2004.
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