Abstract
Hypoxia appears to induce a program which shifts the cellular phenotype toward an increase in extracellular adenosine. Hypoxia-inducible factor-1 (HIF-1) is a key regulator of genes crucial to many aspects of cancer biology. Since in gliomas there is a strong correlation between HIF-1alpha expression, tumor grade and tumor vascularization, the aim of this study was to investigate whether adenosine may regulate HIF-1 in human glioblastoma cell lines. The results indicate that in the human hypoxic A172 and U87MG glioblastoma cell lines adenosine up-regulates HIF-1alpha protein expression via the A(3) receptor subtype. In particular, we investigated the effect of A(3) receptor antagonists on HIF-1 and vascular endothelial growth factor (VEGF) expression. We found that A(3) antagonists inhibit adenosine-induced HIF-1alpha and VEGF protein accumulation in the hypoxic cells. Investigations in the molecular mechanism showed that A(3) receptor stimulation activates p44/p42 and p38 MAPKs that are required for A(3)-induced increase of HIF-1alpha and VEGF. Further studies are required to demonstrate the in vivo relevance of these observations with regard to the proposed role for adenosine as a key element in hypoxia and in tumors.
MeSH terms
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Adenosine / pharmacology*
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Adenosine A3 Receptor Antagonists
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Blotting, Western
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Cell Hypoxia / physiology
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Cell Line, Tumor
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Dose-Response Relationship, Drug
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Enzyme-Linked Immunosorbent Assay
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Gene Expression Regulation, Neoplastic / drug effects*
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Gene Silencing
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Glioblastoma / drug therapy*
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Glioblastoma / metabolism
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Humans
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Hypoxia-Inducible Factor 1, alpha Subunit / genetics
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Hypoxia-Inducible Factor 1, alpha Subunit / metabolism*
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Mitogen-Activated Protein Kinase 1 / metabolism
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Mitogen-Activated Protein Kinase 3 / metabolism
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Phenylurea Compounds / pharmacology
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RNA, Messenger / metabolism
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RNA, Small Interfering / genetics
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RNA, Small Interfering / metabolism
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Receptor, Adenosine A3 / metabolism
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Reverse Transcriptase Polymerase Chain Reaction
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Triazoles / pharmacology
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Up-Regulation
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Vascular Endothelial Growth Factor A / genetics
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Vascular Endothelial Growth Factor A / metabolism*
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p38 Mitogen-Activated Protein Kinases / metabolism
Substances
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Adenosine A3 Receptor Antagonists
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HIF1A protein, human
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Hypoxia-Inducible Factor 1, alpha Subunit
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MRE 3008-F20
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Phenylurea Compounds
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RNA, Messenger
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RNA, Small Interfering
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Receptor, Adenosine A3
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Triazoles
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VEGFA protein, human
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Vascular Endothelial Growth Factor A
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Mitogen-Activated Protein Kinase 1
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Mitogen-Activated Protein Kinase 3
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p38 Mitogen-Activated Protein Kinases
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Adenosine