Mechanism of inhibition by cyclic AMP of protein kinase C-triggered respiratory burst in Ehrlich ascites tumour cells.
The superoxide anion generation in Ehrlich ascites tumour (EAT) cells increased more than two-fold in the presence of the tumour promoter, tetradecanoyl phorbol myristate acetate (TPA). Epinephrine and dibutryl cAMP (Bt2 cAMP) inhibited in a dose-dependent manner, both basal and TPA-triggered superoxide generation in EAT cells. The kinetics of inhibition of superoxide generation showed a maximum inhibition between 30 and 40 min of preincubation with epinephrine or Bt2 cAMP of EAT cells and coincided with an increase in activity of a phosphoprotein phosphatase. In TPA-treated EAT cells, epinephrine or Bt2 cAMP increased the phosphatase activity in a dose-dependent manner. In vitro EGTA, EDTA and sodium fluoride inhibited phosphatase activity. Superoxide generation in response to TPA in Triton-permeabilized EAT cells was inhibited by inclusion of the phosphatase in the assay. Taken together, these results clearly suggest that the phosphatase activity in EAT cells develops as a result of protein kinase A (PKA) and protein kinase C (PKC)-mediated phosphorylation of the phosphatase which then mediates dephosphorylation of the PKC-triggered phosphorylation of proteins to inhibit respiratory burst. A cross-talk between PKA and PKC pathways negatively modulates superoxide generation in EAT cells.
Salimath
B P
BP
Department of Biochemistry, University of Mysore, India.
Savitha
G
G
D000818:Animals; D003994:Bucladesine / Q000494:pharmacology; D002286:Carcinoma, Ehrlich Tumor / Q000378:metabolism; D000242:Cyclic AMP / Q000494:pharmacology*; D004837:Epinephrine / Q000494:pharmacology; D007700:Kinetics; D051379:Mice; D010749:Phosphoprotein Phosphatases / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism*; D016897:Respiratory Burst / Q000187:drug effects*; D015398:Signal Transduction; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D003994:Bucladesine; D000242:Cyclic AMP; D011493:Protein Kinase C; D010749:Phosphoprotein Phosphatases; D013755:Tetradecanoylphorbol Acetate; D004837:Epinephrine