title: Involvement of AMP-activated protein kinase in TGF-β-stimulated VEGF             synthesis in osteoblasts.
abstract: It is generally recognized that AMP-activated protein kinase (AMPK) acts as a key regulator of energy homeostasis. We have previously shown that transforming growth factor-β (TGF-β) stimulates synthesis of vascular endothelial growth factor (VEGF) via p44/p42 mitogen-activated protein (MAP) kinase, stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK) and p38 MAP kinase in osteoblast-like MC3T3-E1 cells. In the present study, we investigated whether AMPK is involved in the TGF-β-stimulated VEGF synthesis in osteoblast-like MC3T3-E1 cells. TGF-β time-dependently induced the phosphorylation of the AMPK α-subunit (Thr172) and the AMPK β-subunit (Ser108). Compound C, an AMPK inhibitor, significantly reduced the TGF-β-stimulated VEGF release. The inhibitory effect of compound C was also observed in normal human osteoblasts (NHOst). Although compound C failed to affect the TGF-β-induced phosphorylation of SAPK/JNK, p38 MAP kinase or Smad2, it markedly suppressed the TGF-β-induced phosphorylation of both MEK1/2 and p44/p42 MAP kinase. In addition, compound C significantly suppressed the VEGF mRNA expression induced by TGF-β. Taken together, our results strongly suggest that AMPK is involved in TGF-β-stimulated VEGF synthesis, and that it functions at a point upstream of MEK1/2.
authors.affiliation: Department of Orthopedic Surgery, Nagoya City University Graduate                     School of Medical Sciences, Mizuho-Cho, Mizuho-Ku, Nagoya 467-8601, Japan.
authors.forename: Jun
authors.initials: J
authors.lastname: Mizutani
authors.forename: Haruhiko
authors.initials: H
authors.lastname: Tokuda
authors.forename: Rie
authors.initials: R
authors.lastname: Matsushima-Nishiwaki
authors.forename: Kenji
authors.initials: K
authors.lastname: Kato
authors.forename: Akira
authors.initials: A
authors.lastname: Kondo
authors.forename: Hideo
authors.initials: H
authors.lastname: Natsume
authors.forename: Osamu
authors.initials: O
authors.lastname: Kozawa
authors.forename: Takanobu
authors.initials: T
authors.lastname: Otsuka
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000378:metabolism*; D000818:Animals; D015153:Blotting, Western; D002460:Cell Line; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D051379:Mice; D010006:Osteoblasts / Q000378:metabolism*; D010766:Phosphorylation; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D060888:Real-Time Polymerase Chain Reaction; D015398:Signal Transduction; D051899:Smad2 Protein / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000378:metabolism*; D042461:Vascular Endothelial Growth Factor A / Q000096:biosynthesis*; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
chemical_list: D012333:RNA, Messenger; D051899:Smad2 Protein; C497783:Smad2 protein, mouse; D016212:Transforming Growth Factor beta; D042461:Vascular Endothelial Growth Factor A; D048031:JNK Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D055372:AMP-Activated Protein Kinases