Differential Effect of the Activation of Protein Kinase A on the Protein Synthesis and Secretion in the T‐Helper 2 Cell Line D10.G4.1

The authors analysed the effect of protein kinase A (PKA) activation on the protein synthesis and secretion in the T‐helper 2 cell line D10.G4.1 (D10) using an assay that allows the detection of almost all secreted proteins of a cell. IL‐4 and IL‐10 were quantified. Three groups of secretory products could be defined. The T‐cell receptor (TCR)‐induced production of the first group (A) of proteins including IL‐4 was enhanced by low concentrations of PKA activators. At higher concentrations the enhancement was less marked. The synthesis and secretion of a second group (B) of proteins including IL‐10 remained unaffected. The production of a third group (C) of proteins was inhibited in a concentration‐dependent manner. Biochemical analysis revealed a block of phospholipase C γ (PLCγ) activity by PKA activators. When D10 cells were stimulated by a phorbol ester plus calcium ionophore the production of group A proteins was enhanced almost fourfold, whereas production of group B proteins was unaffected by PKA activation. This effect was observed at all concentrations of various PKA activators tested. The secretion of group C proteins was no longer inhibited. The same results were obtained when analysing IL‐4 and IL‐10 m‐RNA by Northern blotting. The data demonstrate a lymphokine specific mode of action on a single cell basis. Furthermore, it suggests that the inhibitory action of PKA in D10 cells is due partly to blocking of PLCγ activity.