Regulation of phospholipase D activity in a human oligodendroglioma cell line (HOG).
Oligodendroglial cells express many specific proteins, such as myelin basic protein (MBP), which are physiologically phosphorylated by protein kinase C (PKC). Diacylglycerols are physiological activators of PKC and can be liberated from phospholipids by the direct receptor-mediated activation of phospholipase C (PL-C) or indirectly via the activation of phospholipase D (PL-D). In a well-characterized human oligodendroglioma (HOG) cell line, PL-C (measured by release of [3H]inositol phosphates) and PL-D (formation of [3H]myristoylated or palmitoylated phosphatidylethanol) were activated by both carbachol (blocked by pirenzepine, suggesting an M1 receptor) and histamine (H1 receptor) but not glutamate, bradykinin, or phenylephrine. PL-C stimulation by carbachol or histamine was completely inhibited by short-term treatment (< 30 min) with phorbol ester (TPA), a PKC activator. In contrast, PL-D activation by either carbachol or histamine was stimulated in additive fashion by TPA, suggesting at least two distinct mechanisms for PL-D activation. Down regulation of PKC by prolonged (24 hr) treatment with TPA reversed the inhibitory effects of TPA on PL-C and the stimulatory effects on PL-D. However, the PKC inhibitors H-7 and galactosylsphingosine did not inhibit the TPA-mediated stimulation of PLD while the less-specific PKC inhibitor, staurosporine, was only partially inhibitory. Preexposure of cells to carbachol, greatly reduced both PL-C and PL-D activation by carbachol, suggesting homologous desensitization. Time-course studies indicated that PL-D activation (10 sec or less) was at least as fast as PL-C activation, and the affinity of carbachol and histamine for the receptor coupled to either phospholipase (EC50 = 5-10 microM) was about the same.(ABSTRACT TRUNCATED AT 250 WORDS)
Dawson
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Department of Pediatrics, University of Chicago, IL 60637.
Dawson
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D000470:Alkaloids / Q000494:pharmacology; D002217:Carbachol / Q000494:pharmacology; D002855:Chromatography, Thin Layer; D015536:Down-Regulation / Q000187:drug effects; D004789:Enzyme Activation / Q000187:drug effects; D006632:Histamine / Q000494:pharmacology; D006801:Humans; D006868:Hydrolysis; D007295:Inositol Phosphates / Q000378:metabolism; D009423:Nervous System Neoplasms / Q000201:enzymology*; D009837:Oligodendroglioma / Q000201:enzymology*; D010168:Palmitates / Q000378:metabolism; D010703:Phorbol Esters / Q000494:pharmacology; D010739:Phospholipase D / Q000378:metabolism*; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D019311:Staurosporine; D014407:Tumor Cells, Cultured; D010738:Type C Phospholipases / Q000378:metabolism
D000470:Alkaloids; D007295:Inositol Phosphates; D010168:Palmitates; D010703:Phorbol Esters; D006632:Histamine; D002217:Carbachol; D011493:Protein Kinase C; D010738:Type C Phospholipases; D010739:Phospholipase D; D019311:Staurosporine