Insulin-like growth factor-I stimulates diacylglycerol production via multiple pathways in Balb/c 3T3 cells.
We previously reported that insulin-like growth factor-I (IGF-I) induced sustained calcium cycling across the plasma membrane in primed competent Balb/c 3T3 cells (Kojima, I., Matsunaga, H., Kurokawa, K., Ogata, E., and Nishimoto, I. (1989) J. Biol. Chem. 263, 16561-16567). The present study was conducted to examine whether IGF-I affected cellular metabolism of 1,2-diacylglycerol (1,2-DAG). In primed competent cells prelabeled with [3H]myristate, 1 nM IGF-I caused a 50% increase in [3H]DAG within 10 min. This increase in [3H]DAG was accompanied by 1) a decrease in radioactivity in the glycosylphosphatidylinositol fraction in [3H]glucosamine-labeled cells and a concomitant increase in [3H]inositol-glycan, and 2) a decrease in [3H]phosphatidylcholine and a concomitant elevation of [3H]phosphorylcholine in [3H]choline-labeled cells. When [3H]choline-labeled cells were treated with 10 nM 12-O-tetradecanoylphorbol-4-acetate (TPA), [3H]phosphatidylcholine was reduced by 50%. The TPA-induced reduction of [3H]phosphatidylcholine was completely blocked by 50 microM sphingosine and 50 microM H-7, inhibitors of protein kinase C. Both sphingosine and H-7 attenuated IGF-I-mediated reduction of [3H]phosphatidylcholine. In addition, treatment with IGF-I for 3 h or more resulted in sustained increase in 1,2-DAG mass, which was attenuated by cycloheximide. The increase in DAG mass was accompanied by enhanced incorporation of [14C]glucose into 1,2-DAG. These results indicate that, in primed competent Balb/c 3T3 cells, IGF-I stimulates 1,2-DAG production via multiple pathways and that IGF-I may induce breakdown of phosphatidylcholine by a mechanism involving protein kinase C.
Kojima
I
I
Institute of Endocrinology, Gumma University, Maebashi, Japan.
Kitaoka
M
M
Ogata
E
E
D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D000818:Animals; D016718:Arachidonic Acid; D001095:Arachidonic Acids / Q000378:metabolism; D002460:Cell Line; D004075:Diglycerides / Q000096:biosynthesis*; D005947:Glucose / Q000378:metabolism; D005990:Glycerol / Q000378:metabolism; D007294:Inositol / Q000378:metabolism; D007306:Insecticides / Q000494:pharmacology; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D007546:Isoquinolines / Q000494:pharmacology; D007700:Kinetics; D051379:Mice; D008807:Mice, Inbred BALB C; D019814:Myristic Acid; D009227:Myristic Acids / Q000378:metabolism; D010710:Phosphates / Q000378:metabolism; D010879:Piperazines / Q000494:pharmacology; D047428:Protein Kinase Inhibitors; D011722:Pyrethrins / Q000494:pharmacology; D013110:Sphingosine / Q000494:pharmacology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D001095:Arachidonic Acids; D004075:Diglycerides; D007306:Insecticides; D007546:Isoquinolines; D009227:Myristic Acids; D010710:Phosphates; D010879:Piperazines; D047428:Protein Kinase Inhibitors; D011722:Pyrethrins; D019814:Myristic Acid; D016718:Arachidonic Acid; D007294:Inositol; D007334:Insulin-Like Growth Factor I; D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D005947:Glucose; D013110:Sphingosine; D013755:Tetradecanoylphorbol Acetate; D005990:Glycerol; C009424:tetramethrin