Evidence for modulation of osteocalcin containing gamma-carboxyglutamic acid residues synthesis by insulin-like growth factor-I and vitamin K2 in human osteosarcoma cell line MG-63.
The effect of insulin-like growth factor-I (IGF-I) and 2-methyl-3-all-trans-tetraphenyl-1,4-naphtoquinone (vitamin K2) on the synthesis of osteocalcin containing gamma-carboxyglutamic acid (Gla) residues which is the physiologically relevant form in bone metabolism was studied in cultured human osteoblast-like (MG-63) cells. Both IGF-I and vitamin K2 stimulated 1,25-dihydroxyvitamin D3 (1,25(OH)2D3)-induced osteocalcin containing Gla secretion in a concentration-dependent manner. This stimulatory effect of IGF-I and vitamin K2 was additive. Vitamin K2-enhanced osteocalcin containing Gla secretion was selectively suppressed by 3-(alpha-acetonyl-benzyl)-4-hydroxy-coumarin (warfarin). The stimulatory effect of IGF-I was completely abolished by the presence of cycloheximide; in contrast the effect of vitamin K2 was still observed in the presence of cycloheximide. Treatment of MG-63 cells with IGF-I caused an approximately 2.2-fold increase in osteocalcin mRNA levels (determined by reverse transcription-polymerase chain reaction). Vitamin K2 had no effect on either the stimulation of mRNA level by IGF-I or the basal level. IGF-I-stimulated osteocalcin containing Gla secretion was inhibited by one of its binding proteins (insulin-like growth factor binding protein-4) in a concentration-dependent manner. These findings suggest that the modes of action of IGF-I and vitamin K2 on 1.25(OH)2D3-induced osteocalcin containing Gla secretion in MG-63 cells are different.
Kudo
Y
Y
Department of Obstetrics and Gynecology, Tokyo Women's Medical College, Japan.
Iwashita
M
M
Takeda
Y
Y
Muraki
T
T
D015055:1-Carboxyglutamic Acid / Q000032:analysis*; D003513:Cycloheximide / Q000494:pharmacology; D006801:Humans; D018974:Insulin-Like Growth Factor Binding Protein 4 / Q000494:pharmacology; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D010006:Osteoblasts / Q000187:drug effects* / Q000378:metabolism; D015675:Osteocalcin / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D012516:Osteosarcoma; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D012333:RNA, Messenger / Q000096:biosynthesis; D013268:Stimulation, Chemical; D014407:Tumor Cells, Cultured; D014812:Vitamin K / Q000494:pharmacology*; D014859:Warfarin / Q000494:pharmacology
D018974:Insulin-Like Growth Factor Binding Protein 4; D011500:Protein Synthesis Inhibitors; D012333:RNA, Messenger; D015675:Osteocalcin; D014812:Vitamin K; D015055:1-Carboxyglutamic Acid; D014859:Warfarin; D007334:Insulin-Like Growth Factor I; D003513:Cycloheximide