Stabilization of hypoxia-inducible factor-1alpha is involved in the hypoxic stimuli-induced expression of vascular endothelial growth factor in osteoblastic cells.
It has been suggested that blood vessel formation is an important event coupled to bone formation. The expression of vascular endothelial growth factor (VEGF), a potent angiogenic factor, has been shown to be greatly stimulated in osteoblasts by hypoxic stimuli such as deprivation of oxygen and treatment with cobalt. In other cell types, hypoxia-inducible factor-1 (HIF-1) that binds hypoxia-response element (HRE) has been shown to mediate gene expression induced by hypoxic stimuli. In this study, we investigated the effects of hypoxic stimuli on HIF-1, HRE, and VEGF in osteoblastic cell lines. Exposure of these cells to hypoxia or cobalt resulted in a great increase in the protein level of HIF-1alpha and the gene expression of VEGF. Transforming growth factor-beta1, prostaglandin E2, dexamethasone, and 1,25-dihydroxyvitamin D3 that have been shown to regulate VEGF gene expression in osteoblasts had no effect on HIF-1alpha induction. Blocking the enzymatic activity of phosphatidylinositol 3-kinase, p38, MEK-1 did not have any effect on the cobalt-stimulated increase of HIF-1alpha in these cells. In contrast, N-acetylcysteine (NAC), a scavenger of reactive oxygen species, abolished the cobalt induction of HIF-1alpha and that of the VEGF and a HRE-driven reporter genes. However, the hypoxia responses were not affected by NAC. These findings suggest that hypoxia and cobalt can induce VEGF gene expression in osteoblasts by increasing the level of HIF-1alpha protein through different mechanisms.
Kim
Hong-Hee
HH
National Research Laboratory for Bone Metabolism, Chosun University, Kwangju, Korea.
Lee
Shee Eun
SE
Chung
Woon Jae
WJ
Choi
Youngyeon
Y
Kwack
KyuBum
K
Kim
Si Wouk
SW
Kim
Myong Soo
MS
Park
Hyunsung
H
Lee
Zang Hee
ZH
D000111:Acetylcysteine / Q000737:chemistry; D015153:Blotting, Western; D002117:Calcitriol / Q000494:pharmacology; D002460:Cell Line; D003035:Cobalt / Q000494:pharmacology; D003907:Dexamethasone / Q000494:pharmacology; D015232:Dinoprostone / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D016228:Endothelial Growth Factors / Q000096:biosynthesis* / Q000737:chemistry; D016166:Free Radical Scavengers / Q000494:pharmacology; D015870:Gene Expression; D005938:Glucocorticoids / Q000494:pharmacology; D006801:Humans; D000860:Hypoxia; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D008156:Luciferases / Q000378:metabolism; D008222:Lymphokines / Q000096:biosynthesis* / Q000737:chemistry; D048728:MAP Kinase Kinase Kinase 1; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D010006:Osteoblasts / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D017382:Reactive Oxygen Species; D020218:Response Elements; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013997:Time Factors; D014157:Transcription Factors / Q000737:chemistry* / Q000378:metabolism*; D014162:Transfection; D016212:Transforming Growth Factor beta / Q000494:pharmacology; D053773:Transforming Growth Factor beta1; D015854:Up-Regulation; D042461:Vascular Endothelial Growth Factor A; D042442:Vascular Endothelial Growth Factors; D048051:p38 Mitogen-Activated Protein Kinases
D000111:Acetylcysteine; D002117:Calcitriol; D003035:Cobalt; D003907:Dexamethasone; D015232:Dinoprostone; D016228:Endothelial Growth Factors; D016166:Free Radical Scavengers; D005938:Glucocorticoids; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D008156:Luciferases; D008222:Lymphokines; D048728:MAP Kinase Kinase Kinase 1; D020928:Mitogen-Activated Protein Kinases; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D012333:RNA, Messenger; D017382:Reactive Oxygen Species; D014157:Transcription Factors; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; D042461:Vascular Endothelial Growth Factor A; D042442:Vascular Endothelial Growth Factors; D048051:p38 Mitogen-Activated Protein Kinases; C497442:HIF1A protein, human; C508960:TGFB1 protein, human; C482576:MAP3K1 protein, human