Phosphatidylcholine-specific phospholipase C, but not phospholipase D, is involved in pemphigus IgG-induced signal transduction

The precise mechanism of the acantholysis after pemphigus IgGs bind to desmoglein (Dsg) 3 and/or Dsg 1 on the cell surface is as yet unknown, We have previously reported that pemphigus IgG (P-IgG) causes a transient increase in intracellular calcium and inositol 1,4,5-trisphosphate concentration, and subsequent activation of protein kinase C (PKC) in DJM-1 cells, a squamous cell carcinoma line, In order to see whether phosphatidylcholine (PC)-specific phospholipase C (PLC) or phospholipase D (PLD) is involved in the P-IgG-induced signaling process, the production of 1,2-diacylglycerol (DAG) and phosphatidylbutanol (PBut), a potential marker for the determination of PLD activity in the presence of butanol, was determined in DJM-1 cells, A biphasic accumulation of DAG, which consisted of a first transient phase and a second sustained phase, was observed, The second phase of DAG accumulation was profoundly inhibited by pretreatment with D609, a selective inhibitor of PC-PLC, but not by propranolol, an inhibitor of phosphatidate phosphohydrolase, Pemphigus serum after preadsortion of antibodies to Dsg 3 and Dsg 1 with recombinant Dsg 3 and Dsg 1 did not show formation of DAG, PBut was not generated following the addition of P-IgG, In addition, the levels of [H-3]phosphocholine, a direct metabolite of PC-PLC, were elevated after the addition of P-IgG, These results suggest that the PC-PLC pathway plays a major role in P-IgG-induced transmembrane signaling by causing prolonged generation of DAG, which may lead to long-term activation of PKC.