Differential inhibitory effects of 2-azafluorenones on PI-PLC activation but not on PC-PLC- or PC-PLD-activation induced by histamine, PAF, PMA or A23187 in C6 glioma cells.
In this study, C6 glioma cells were used to test the effects of 2-azafluorenone and its related compounds on membrane phosphatidylinositol (PI) and phosphatidylcholine (PC) turnover.  An increase of [³H]-labeled inositol phosphate (IP1) formation by histamine (100 μM) or A23187 (100 nM) via the activation of phosphatidylinositol-specific phospholipase C (PI-PLC) to breakdown labeled substrate was observed, and this effect could be partially blocked by about half at 100 μM of 2-azafluorenones. Histamine induced the increase of IP1 formation, but failed to cause an increase in extracellularly releasing of [3H]choline metabolites, or intracellular accumulation of [³H]phosphscholine.  However, platelet activation factor (PAF) from 0.2 to 1 μM, and phorbol 12-myristate-13-acetate (PMA) at 1 μM caused an increase in extracellularly releasing of [³H]choline metabolites, and intracellular accumulation of [³H]phosphocholine via the activation on phosphatidylcholine (PC)-PLC.  These responses of PAF and PMA were not affected by 2-azafluorenone or 4-methyl-2-azafluorenone even at high concentration (10⁻⁴ M).  A23187 induced an increase of intracellular [³H]choline release via the activation of PCphospholipase D (PLD).  This increasing effect of 100 nM A23187 was not affected by 2-azafluorenone or 4-methyl-2-azafluorenone even at a high concentration of 10⁻⁴ M.  In summary, the inhibitory effect of 2-azafluorenone and its related compound 4-methyl-2-azafluorenone was observed selectively on PIPLC, but not on PC-PLC or PC-PLD based on changes of products after the activation of these enzymes.
Institute of Neuroscience, National Yang Ming University, Shih-Pai, Beitou Taipei 112, Taiwan, R.O.C.
Hai-Long
HL
Wang
Li-Chuan
LC
Wang
Jiann-Wu
JW
Wei
D000818:Animals; D000001:Calcimycin; D045744:Cell Line, Tumor; D004789:Enzyme Activation / Q000187:drug effects; D005449:Fluorenes / Q000494:pharmacology*; D006632:Histamine; D010713:Phosphatidylcholines / Q000378:metabolism; D010716:Phosphatidylinositols / Q000378:metabolism; D054801:Phosphoinositide Phospholipase C / Q000187:drug effects* / Q000378:metabolism; D010739:Phospholipase D / Q000187:drug effects* / Q000378:metabolism; D010972:Platelet Activating Factor; D051381:Rats; D013755:Tetradecanoylphorbol Acetate; D014316:Tritium; D010738:Type C Phospholipases / Q000187:drug effects* / Q000378:metabolism
D005449:Fluorenes; D010713:Phosphatidylcholines; D010716:Phosphatidylinositols; D010972:Platelet Activating Factor; D014316:Tritium; D000001:Calcimycin; D006632:Histamine; D010738:Type C Phospholipases; D054801:Phosphoinositide Phospholipase C; C105598:phosphatidylcholine-specific phospholipase C; D010739:Phospholipase D; D013755:Tetradecanoylphorbol Acetate