Activation of phosphatidylinositol 3-kinase by concanavalin A through dual signaling pathways, G-protein-coupled and phosphotyrosine-related, and an essential role of the G-protein-coupled signals for the lectin-induced respiratory burst in human monocytic THP-1 cells.
Stimulation of monocytic THP-1 cells by a lectin, concanavalin A (Con A), resulted in protein-tyrosine phosphorylation and association of some of the thus phosphorylated proteins with the 85 kDa regulatory subunit of PtdIns 3-kinase. Both actions of Con A were not inhibited by wortmannin, a PtdIns 3-kinase inhibitor, or by prior exposure of cells to pertussis toxin which uncouples certain G-proteins from receptors. The binding of PtdIns 3-kinase to the tyrosine-phosphorylated proteins increased upon Con A stimulation; there was a marked increase in the enzymic activity in the anti-phosphotyrosine immuno-precipitates from Con A-treated cells. The increase was abolished by wortmannin but not affected by pertussis toxin. The incorporation of 32P into PtdInsP3 also increased during incubation of [32P]P(i)-prelabelled cells with Con A, reflecting activation of whole-cell PtdIns 3-kinase which could not be accounted for solely by the increase in the phosphotyrosine-bound enzyme activity from the following aspects: (1) different concentration dependencies for Con A; and (2) almost total susceptibility of the incorporation to pertussis toxin. This notion appears to be supported by different time courses between increases in PtdInsP3 production and the phosphotyrosine-bound activity. The susceptibility to the toxin may reflect involvement of the toxin-sensitive G-proteins. In contrast, insulin-induced increases in PtdInsP3 production, as well as increases in phosphotyrosine-bound PtdIns 3-kinase activity, were blocked by wortmannin, but never affected by prior exposure of cells to pertussis toxin, excluding a possible involvement of G-proteins in the insulin-induced activation. Con-A-induced O2- production was almost inhibited by either pertussis toxin or wortmannin. These results suggest that oligomerization of cell-surface glycoproteins with Con A gives rise to activation of G-protein(s) and certain tyrosine kinase(s), both of which were responsible for PtdIns 3-kinase activation; the G-protein-mediated activation led to the respiratory burst.
Matsuo
T
T
Ui Laboratory, Institute of Physical and Chemical Research, Wako-shi, Japan.
Hazeki
K
K
Hazeki
O
O
Katada
T
T
Ui
M
M
D000595:Amino Acid Sequence; D000730:Androstadienes / Q000494:pharmacology; D002460:Cell Line; D003208:Concanavalin A / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006801:Humans; D007328:Insulin / Q000494:pharmacology; D055504:Insulin Receptor Substrate Proteins; D007700:Kinetics; D008562:Membrane Glycoproteins / Q000378:metabolism; D008969:Molecular Sequence Data; D009000:Monocytes / Q000187:drug effects / Q000378:metabolism*; D037342:Pertussis Toxin; D019869:Phosphatidylinositol 3-Kinases; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000037:antagonists & inhibitors / Q000378:metabolism*; D019000:Phosphotyrosine / Q000378:metabolism; D016897:Respiratory Burst; D015398:Signal Transduction; D010566:Virulence Factors, Bordetella / Q000494:pharmacology; D000077191:Wortmannin
D000730:Androstadienes; D004791:Enzyme Inhibitors; C526292:IRS1 protein, human; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; D008562:Membrane Glycoproteins; D010750:Phosphoproteins; D010566:Virulence Factors, Bordetella; D003208:Concanavalin A; D019000:Phosphotyrosine; D037342:Pertussis Toxin; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor); D019204:GTP-Binding Proteins; D000077191:Wortmannin