Interleukin-11 induces phosphatidic acid formation and activates MAP kinase in mouse 3T3-L1 cells

Interleukin-11 (IL-11) stimulated [3H]phosphatidic acid (PA) formation in [3H]arachidonic acid (AA) prelabelled quiescent mouse 3T3-L1 cells. When IL-11 stimulated 3T3-L1 cells were incubated with NaF, a phosphatidic acid phosphohydrolase (PAP) inhibitor, increased PA formation was observed. In the presence of ethanol, phosphatidylethanol accumulated at the expense of PA. These results indicated that the formation of PA upon IL-11 stimulation was a result of phospholipase D (PLD) activation. Endogenous accumulation of PA by NaF treatment or exogenously added PA enhanced tyrosine phosphorylation of two proteins of 44 KDa (p44) and 47 KDa (p47) whereas tyrosine phosphorylation of other proteins was not affected. Among various PA species, dipalmitoyl PA was found to be most effective in enhancing tyrosine phosphorylation of these proteins. p44 and p47 cross reacted with anti-MAP kinase monoclonal antibody (MoAb) in both immunoprecipitation and western blot analysis. Lysates from IL-11-induced or PA-induced cells stimulated phosphorylation of a synthetic peptide substrate for MAP kinase, indicating the activation of MAP kinase in the induced cells. These studies suggest that one of the cellular signalling mechanisms of IL-11 in 3T3-L1 cells involves the activation of phospholipase D to produce the second messenger PA. The increased level of PA enhances tyrosine phosphorylation of p44 and p47 which belong to the members of MAP kinase family and thus transduces some of the mitogenic signals of IL-11 in this cell line.