Activation of p38 MAPK and/or JNK contributes to increased levels of VEGF secretion in human malignant glioma cells.
Malignant gliomas are typically angiogenic and secrete high levels of VEGF. Hypoxia has been identified as an important regulator of VEGF. However, malignant gliomas express high levels of VEGF in both hypoxic perinecrotic and vital tumor areas. In this study, we examined intracellular signaling pathways involved in the secretion of VEGF in glioma cells under normoxic conditions. Human malignant glioma cell lines, T98G, U373MG, U87MG, and A172, and human fetal lung fibroblasts (HFL) were cultured both with and without IL-1beta under normoxic conditions. VEGF, IL-1, IL-6, and TNF-alpha were measured with ELISA. VEGF mRNA levels were estimated by RT-PCR. Inhibitors of COX-2, MAPK, and phosphatidyl inositol 3-kinase (PI3-K), and blocking antibodies to TGF-beta II and TNF-alpha, or IL-1 receptor antagonist, were used to examine their effects on VEGF secretion. Phosphorylation of MAPK was examined by immunoblotting. The basal levels of VEGF secretion were significantly higher in U87MG, U373MG, and T98G, than HFL. IL-1beta significantly stimulated VEGF secretion in these glioma cells. Inhibitors of p38 MAPK and/or JNK significantly suppressed VEGF secretion both in the presence and absence of IL-1beta, while inhibitors of COX-2, ERK1/2, and PI3-K did not. Constitutive phosphorylation of p38 MAPK and JNK was observed in these glioma cells. The levels of IL-1beta in U87MG were significantly higher than in other glioma cell lines, and IL-1 receptor antagonist suppressed basal secretion of VEGF from U87MG. In conclusion, p38 MAPK and JNK pathways play an important role in VEGF secretion from malignant glioma cells under normoxic conditions, possibly contributing to VEGF-induced angiogenesis in malignant gliomas at vital tumor areas where there is no hypoxia.
Yoshino
Yoshikazu
Y
Department of Neurosurgery, Graduate School, Tokyo Medical and Dental University, Tokyo 113-8519, Japan. yyoshino@tdmc.hosp.go.jp
Aoyagi
Masaru
M
Tamaki
Masashi
M
Duan
Lian
L
Morimoto
Takashi
T
Ohno
Kikuo
K
D001932:Brain Neoplasms / Q000201:enzymology / Q000378:metabolism*; D045744:Cell Line, Tumor; D051546:Cyclooxygenase 2 / Q000378:metabolism; D004789:Enzyme Activation; D005910:Glioma / Q000201:enzymology / Q000378:metabolism*; D006801:Humans; D053583:Interleukin-1beta / Q000494:pharmacology; D048670:MAP Kinase Kinase 4 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D008565:Membrane Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000037:antagonists & inhibitors / Q000378:metabolism; D010766:Phosphorylation; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism*; D048051:p38 Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*
D053583:Interleukin-1beta; D008565:Membrane Proteins; D047428:Protein Kinase Inhibitors; D042461:Vascular Endothelial Growth Factor A; D051546:Cyclooxygenase 2; C496540:PTGS2 protein, human; D048052:Mitogen-Activated Protein Kinase 3; D048051:p38 Mitogen-Activated Protein Kinases; D048670:MAP Kinase Kinase 4