Stimulatory effect of a phorbol ester on expression of insulin-like growth factor (IGF) binding protein-2 and level of IGF-I receptors in mouse osteoblastic MC3T3-E1 cells.
We examined the relationship between signal transduction and the expression of insulin-like growth factor I (IGF-I), IGF-I receptor level, and IGF binding proteins (IGFBPs) in murine clonal osteoblastic MC3T3-E1 cells. 12-O-Tetradecanoylphorbol-13-acetate (TPA), an activator of protein kinase C, decreased the secretion of immunoreactive IGF-I into the medium, whereas dibutyryl cAMP (Bt2cAMP) augmented the secretion. In contrast, TPA increased the level of type I IGF receptor on the cells. Furthermore, MC3T3-E1 cells produced and secreted at least three different IGFBPs with molecular masses of 24, 30, and 34 kDa, and the 24-kDa IGFBP was predominant under normal conditions. However, TPA specifically increased the secretion of the 34-kDa IGFBP. The N-terminal amino acid sequence of the purified 34-kDa IGFBP was nearly identical with that of rat IGFBP-2. Furthermore, the 34-kDa IGFBP was immunoreactive to anti-IGFBP-2 antiserum. The level of IGFBP-2 mRNA in the cells was increased by TPA, indicating that the increase in IGFBP-2 secretion results from the stimulation of IGFBP-2 production. In contrast, Bt2cAMP affected neither IGF-I receptor number nor the IGFBP secretion. These results indicate that the production of IGF-I and the expression of IGF-I receptors and IGFBP-2 are up-regulated by the activation of adenylate cyclase and protein kinase C, respectively, in osteoblastic MC3T3-E1 cells.
Hakeda
Y
Y
Department of Oral Anatomy, Meikai University School of Dentistry, Saitama, Japan.
Yoshizawa
K
K
Hurley
M
M
Kawaguchi
H
H
Tezuka
K
K
Tanaka
K
K
Satoh
T
T
Kumegawa
M
M
D000262:Adenylyl Cyclases / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D003994:Bucladesine / Q000494:pharmacology; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D004789:Enzyme Activation; D018971:Insulin-Like Growth Factor Binding Protein 2; D007335:Insulin-Like Growth Factor II / Q000032:analysis / Q000378:metabolism; D051379:Mice; D008969:Molecular Sequence Data; D010006:Osteoblasts / Q000737:chemistry* / Q000166:cytology* / Q000648:ultrastructure; D010703:Phorbol Esters / Q000494:pharmacology*; D011493:Protein Kinase C / Q000378:metabolism; D012333:RNA, Messenger / Q000032:analysis / Q000235:genetics; D017526:Receptor, IGF Type 1 / Q000032:analysis* / Q000235:genetics / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D002352:Carrier Proteins; D018971:Insulin-Like Growth Factor Binding Protein 2; D010703:Phorbol Esters; D012333:RNA, Messenger; D003994:Bucladesine; D007335:Insulin-Like Growth Factor II; D017526:Receptor, IGF Type 1; D011493:Protein Kinase C; D000262:Adenylyl Cyclases; D013755:Tetradecanoylphorbol Acetate