IGF-I regulates tight-junction protein claudin-1 during differentiation of osteoblast-like MC3T3-E1 cells via a MAP-kinase pathway.
Insulin-like growth factor I (IGF-I) is expressed in many tissues, including bone, and acts on the proliferation and differentiation of osteoblasts as an autocrine/paracrine regulator. Tight-junction proteins have been detected in osteoblasts, and direct cell-to-cell interactions may modulate osteoblast function with respect, for example, to gap junctions. In order to investigate the regulation of expression of tight-junction molecules and of function during bone differentiation, osteoblast-like MC3T3-E1 cells and osteocyte-like MLO-Y4 cells were treated with IGF-I. In both MC3T3-E1 cells and MLO-Y4 cells, the tight-junction molecules occludin, claudin-1, -2, and -6, and the gap-junction molecule connexin 43 (Cx43) were detected by reverse transcription with polymerase chain reaction. In MC3T3-E1 cells but not MLO-Y4 cells, mRNAs of claudin-1, -2, and -6, Cx43, and type I collagen, and proteins of claudin-1 and Cx43 were increased after treatment with IGF-I. Such treatment significantly decreased paracellular permeability in MC3T3-E1 cells. The expression of claudin-1 in MC3T3-E1 cells after IGF-I treatment was mainly upregulated via a mitogen-activated protein (MAP)-kinase pathway and, in part, modulated by a PI3-kinase pathway, whereas Cx43 expression and the mediated gap-junctional intercellular communication protein did not contribute to the upregulation. Furthermore, in MC3T3-E1 cells during wound healing, upregulation of claudin-1 was observed together with an increase of IGF-I and type I collagen. These findings suggest that the induction of tight-junction protein claudin-1 and paracellular permeability during the differentiation of osteoblast-like MC3T3-E1 cells after treatment with IGF-I is regulated via a MAP-kinase pathway, but not with respect to gap junctions.
Department of Orthopaedic Surgery, Sapporo Medical University School of Medicine, S1, W17, Sapporo, 060-8556, Japan.
Naoko
N
Hatakeyama
Takashi
T
Kojima
Kousuke
K
Iba
Masaki
M
Murata
Mia M
MM
Thi
David C
DC
Spray
Makoto
M
Osanai
Hideki
H
Chiba
Sumio
S
Ishiai
Toshihiko
T
Yamashita
Norimasa
N
Sawada
D000818:Animals; D002454:Cell Differentiation / Q000187:drug effects; D002460:Cell Line; D002463:Cell Membrane Permeability / Q000187:drug effects; D062445:Claudin-1; D024042:Collagen Type I / Q000187:drug effects / Q000378:metabolism; D018031:Connexin 43 / Q000187:drug effects / Q000378:metabolism; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology / Q000502:physiology*; D008565:Membrane Proteins / Q000096:biosynthesis* / Q000187:drug effects / Q000378:metabolism; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000187:drug effects / Q000378:metabolism*; D062793:Occludin; D010006:Osteoblasts / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000187:drug effects / Q000378:metabolism; D015854:Up-Regulation / Q000187:drug effects; D014945:Wound Healing
D062445:Claudin-1; C568113:Cldn1 protein, mouse; D024042:Collagen Type I; D018031:Connexin 43; D008565:Membrane Proteins; D062793:Occludin; C568986:Ocln protein, mouse; D007334:Insulin-Like Growth Factor I; D019869:Phosphatidylinositol 3-Kinases; D020928:Mitogen-Activated Protein Kinases