Protein kinases A and C positively regulate G protein-dependent activation of phosphatidylinositol-specific phospholipase C by tumor necrosis factor-alpha in MC3T3-E1 osteoblasts.
The role(s) of protein kinases in the regulation of G protein-dependent activation of phosphatidylinositol-specific phospholipase C by tumor necrosis factor-alpha was investigated in the osteoblast cell line MC3T3-E1. We have previously reported the stimulatory effects of tumor necrosis factor-alpha and A1F4-, an activator of G proteins, on this phospholipase pathway documented by a decrease in mass of PI and release of diacylglycerol. In this study, we further explored the mechanism(s) by which the tumor necrosis factor or A1F4(-)-promoted breakdown of phosphatidylinositol and the polyphosphoinositides by phospholipase C is regulated. Tumor necrosis factor-alpha was found to elicit a 4-5-fold increase in the formation of [3H]inositol-1,4-phosphate and [3H]inositol-1,4,5-phosphate; and a 36% increase in [3H]inositol-1-phosphate within 5 min in prelabeled cells. [3H]inositol-4-phosphate, a metabolite of [3H]inositol-1,4-phosphate and [3H]inositol-1,4,5-phosphate, was found to be the predominant phosphoinositol product of tumor necrosis factor-alpha and A1F4(-)-activated phospholipase C hydrolysis after 30 min. In addition, the preincubation of cells with pertussis toxin decreased the tumor necrosis factor-induced release of inositol phosphates by 53%. Inhibitors of protein kinase C, including Et-18-OMe and H-7, dramatically decreased the formation of [3H]inositol phosphates stimulated by either tumor necrosis factor-alpha or A1F4- by 90-100% but did not affect basal formation. The activation of cAMP-dependent protein kinase, or protein kinase A, by the treatment of cells with forskolin or 8-BrcAMP augmented basal, tumor necrosis factor-alpha and A1F4(-)-induced [3H]inositol phosphate formation. Therefore, we report that protein kinases can regulate tumor necrosis factor-alpha-initiated signalling at the cell surface in osteoblasts through effects on the coupling between receptor, G-protein and phosphatidylinositol-specific phospholipase C.
Rapuano
B E
BE
Division of Research, Cornell University Medical College, New York, NY, USA.
Bockman
R S
RS
D017607:Aluminum Compounds / Q000494:pharmacology; D000818:Animals; D002460:Cell Line; D005576:Colforsin / Q000494:pharmacology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D004789:Enzyme Activation; D005459:Fluorides / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000502:physiology*; D006801:Humans; D007295:Inositol Phosphates / Q000378:metabolism; D051379:Mice; D010006:Osteoblasts / Q000201:enzymology*; D043265:Phosphatidylinositol Diacylglycerol-Lyase; D054801:Phosphoinositide Phospholipase C; D010727:Phosphoric Diester Hydrolases / Q000378:metabolism*; D011493:Protein Kinase C / Q000378:metabolism*; D011994:Recombinant Proteins; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*
D017607:Aluminum Compounds; D007295:Inositol Phosphates; D011994:Recombinant Proteins; D014409:Tumor Necrosis Factor-alpha; D005576:Colforsin; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D010727:Phosphoric Diester Hydrolases; D054801:Phosphoinositide Phospholipase C; D019204:GTP-Binding Proteins; D043265:Phosphatidylinositol Diacylglycerol-Lyase; D005459:Fluorides; C032311:aluminum fluoride