Phosphatidylcholine-specific phospholipase C inhibitor, tricyclodecan-9-yl xanthogenate (D609), increases phospholipase D-mediated phosphatidylcholine hydrolysis in UMR-106 osteoblastic osteosarcoma cells.
Our previous studies have shown that parathyroid hormone (PTH) stimulates phosphatidylcholine (PC) hydrolysis by phospholipase D (PLD) and transphosphatidylation in UMR-106 osteoblastic cells. To determine whether phospholipase C (PLC) is also involved in the PTH-mediated PC hydrolysis, we used the inhibitor, tricyclodecan-9-yl xanthogenate (D609), a putatively selective antagonist of this pathway. Consistent with this proposed mechanism, D609 decreased (3)H-phosphocholine in extracts from UMR-106 cells prelabeled with (3)H-choline. Unexpectedly, D609 enhanced PC hydrolysis and transphosphatidylation, suggesting that either there was a compensatory increase in PLD activity when PLC was inhibited, or that D609 directly increased PLD activity. The D609-stimulated increase in PC hydrolysis was rapid, being seen as early as 2 min. The effect of D609 was temperature-sensitive, consistent with an enzymatic mechanism. The D609-stimulated increase in PC hydrolysis was PKC-independent, based upon the lack of effect of down-regulation of PKC by phorbol 12,13-dibutyrate on the response. The studies reveal a novel action of this inhibitor on signaling in osteoblastic cells which might influence downstream responses.
Singh
A T
AT
Department of Molecular Pharmacology and Biological Chemistry, Northwestern University Medical School, Chicago, IL 60611-3008, USA. a-singh@nwu.edu
Radeff
J M
JM
Kunnel
J G
JG
Stern
P H
PH
D000970:Antineoplastic Agents / Q000494:pharmacology*; D001859:Bone Neoplasms; D001952:Bridged-Ring Compounds / Q000494:pharmacology*; D002794:Choline / Q000378:metabolism; D015536:Down-Regulation; D004357:Drug Synergism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D006868:Hydrolysis / Q000187:drug effects; D007527:Isoenzymes / Q000037:antagonists & inhibitors; D009636:Norbornanes; D012516:Osteosarcoma; D010281:Parathyroid Hormone / Q000494:pharmacology; D010713:Phosphatidylcholines / Q000378:metabolism*; D015398:Signal Transduction; D013696:Temperature; D013859:Thiocarbamates; D013871:Thiones / Q000494:pharmacology*; D014316:Tritium; D014407:Tumor Cells, Cultured; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors*
D000970:Antineoplastic Agents; D001952:Bridged-Ring Compounds; D004791:Enzyme Inhibitors; D007527:Isoenzymes; D009636:Norbornanes; D010281:Parathyroid Hormone; D010713:Phosphatidylcholines; D013859:Thiocarbamates; D013871:Thiones; D014316:Tritium; C046498:tricyclodecane-9-yl-xanthogenate; D010738:Type C Phospholipases; D002794:Choline