title: Heat shock protein 22 (HSPB8) limits TGF-β-stimulated migration of osteoblasts.
abstract: Heat shock proteins (HSPs) are induced in response to various physiological and environmental conditions such as chemical and heat stress, and recognized to function as molecular chaperones. HSP22 (HSPB8), a low-molecular weight HSP, is ubiquitously expressed in many cell types. However, the precise role of HSP22 in bone metabolism remains to be clarified. In the present study, we investigated whether HSP22 is implicated in the transforming growth factor-β (TGF-β)-stimulated migration of osteoblast-like MC3T3-E1 cells. Although protein levels of HSP22 were clearly detected in unstimulated MC3T3-E1 cells, TGF-β failed to induce the protein levels. The TGF-β-stimulated migration was significantly up-regulated by knockdown of HSP22 expression. The cell migration stimulated by platelet-derived growth factor-BB was also enhanced by HSP22 knockdown. SB203580, an inhibitor of p38 mitogen-activated protein kinase, PD98059, an inhibitor of MEK1/2, or SP600125, an inhibitor of stress-activated protein kinase/c-Jun N-terminal kinase had no effects on the TGF-β-induced migration. SIS3, a specific inhibitor of TGF-β-dependent Smad3 phosphorylation, significantly reduced the migration with or without TGF-β stimulation. Smad2, Smad3, Smad4 or Smad7 was not coimmunoprecipitated with HSP22. On the other hand, the TGF-β-induced Smad2 phosphorylation was enhanced by HSP22 down-regulation. The protein levels of TGF-β type II receptor (TGF-β RII) but not TGF-β type I receptor (TGF-β RI) was significantly up-regulated in HSP22 knockdown cells compared with those in the control cells. However, the levels of TGF-β RII mRNA in HSP22 knockdown cells were little different from those of the control cells. Neither TGF-β RI nor TGF-β RII was coimmunoprecipitated with HSP22. SIS3 reduced the amplification by HSP22 knockdown of the TGF-β-stimulated cell migration almost to the basal level. Our results strongly suggest that HSP22 functions as a negative regulator in the TGF-β-stimulated migration of osteoblasts via suppression of the Smad-dependent pathway, resulting from modulating the protein levels of TGF-β RII.
authors.affiliation: Department of Orthopedic Surgery, Nagoya City University Graduate School of Medical Sciences, Nagoya 467-8601, Japan; Department of Pharmacology, Gifu University Graduate School of Medicine, Gifu 501-1194, Japan.
authors.forename: Naohiro
authors.initials: N
authors.lastname: Yamamoto
authors.affiliation: Department of Pharmacology, Gifu University Graduate School of Medicine, Gifu 501-1194, Japan; Department of Clinical Laboratory, National Center for Geriatrics and Gerontology, Obu, Aichi 474-8511, Japan. Electronic address: tokuda@ncgg.go.jp.
authors.forename: Haruhiko
authors.initials: H
authors.lastname: Tokuda
authors.affiliation: Department of Orthopedic Surgery, Nagoya City University Graduate School of Medical Sciences, Nagoya 467-8601, Japan; Department of Pharmacology, Gifu University Graduate School of Medicine, Gifu 501-1194, Japan.
authors.forename: Gen
authors.initials: G
authors.lastname: Kuroyanagi
authors.affiliation: Department of Orthopedic Surgery, Nagoya City University Graduate School of Medical Sciences, Nagoya 467-8601, Japan; Department of Pharmacology, Gifu University Graduate School of Medicine, Gifu 501-1194, Japan.
authors.forename: Shingo
authors.initials: S
authors.lastname: Kainuma
authors.affiliation: Department of Pharmacology, Gifu University Graduate School of Medicine, Gifu 501-1194, Japan.
authors.forename: Rie
authors.initials: R
authors.lastname: Matsushima-Nishiwaki
authors.affiliation: Department of Orthopedic Surgery, Nagoya City University Graduate School of Medical Sciences, Nagoya 467-8601, Japan; Department of Pharmacology, Gifu University Graduate School of Medicine, Gifu 501-1194, Japan.
authors.forename: Kazuhiko
authors.initials: K
authors.lastname: Fujita
authors.affiliation: Department of Pharmacology, Gifu University Graduate School of Medicine, Gifu 501-1194, Japan.
authors.forename: Osamu
authors.initials: O
authors.lastname: Kozawa
authors.affiliation: Department of Orthopedic Surgery, Nagoya City University Graduate School of Medical Sciences, Nagoya 467-8601, Japan.
authors.forename: Takanobu
authors.initials: T
authors.lastname: Otsuka
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D002460:Cell Line; D002465:Cell Movement / Q000187:drug effects*; D055785:Gene Knockdown Techniques; D050886:HSP20 Heat-Shock Proteins / Q000378:metabolism*; D055551:HSP27 Heat-Shock Proteins / Q000378:metabolism; D006360:Heat-Shock Proteins; D007546:Isoquinolines / Q000494:pharmacology; D051379:Mice; D018832:Molecular Chaperones; D009124:Muscle Proteins / Q000378:metabolism*; D010006:Osteoblasts / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D011485:Protein Binding / Q000187:drug effects; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D011725:Pyridines / Q000494:pharmacology; D011758:Pyrroles / Q000494:pharmacology; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000378:metabolism; D000077293:Receptor, Transforming Growth Factor-beta Type I; D000077294:Receptor, Transforming Growth Factor-beta Type II; D018125:Receptors, Transforming Growth Factor beta / Q000235:genetics / Q000378:metabolism; D051785:Smad Proteins / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000494:pharmacology*
chemical_list: C508504:6,7-dimethyl-2-(2E)-3-(1-methyl-2-phenyl-1H-pyrrolo(2,3-b)pyridin-3-yl-prop-2-enoyl)-1,2,3,4-tetrahydroisoquinoline hydrochloride; D050886:HSP20 Heat-Shock Proteins; D055551:HSP27 Heat-Shock Proteins; D006360:Heat-Shock Proteins; C490206:Hspb8 protein, mouse; D007546:Isoquinolines; D018832:Molecular Chaperones; D009124:Muscle Proteins; D047428:Protein Kinase Inhibitors; D011725:Pyridines; D011758:Pyrroles; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D018125:Receptors, Transforming Growth Factor beta; D051785:Smad Proteins; D016212:Transforming Growth Factor beta; D017346:Protein Serine-Threonine Kinases; D000077293:Receptor, Transforming Growth Factor-beta Type I; D000077294:Receptor, Transforming Growth Factor-beta Type II
keywords: HSPB8; Heat shock protein 22; Migration; Osteoblast; Transforming growth factor-β