Demonstration of cell-specific phosphorylation of LTC4 synthase

PMA-induced leukotriene C4 synthase (LTC4S) phosphorylation was investigated over a period of 8 h in a monocytic cell line (THP-1). The level of LTC4S phosphorylation was increased 3-5 fold over a 4 h period decreasing to basal levels after 8 h. This phosphorylation event was found to be specific to THP-1 cells as there was a lack of LTC4S phosphorylation in both COS-7 and K-562 cells, and was also found to be dependent on the cellular confluency. In the presence of specific protein kinase C (PKC) inhibitors, a dose-dependent inhibition of the phosphorylation of LTC4S became evident, an effect not seen with PKA and tyrosine kinase inhibitors. This represents the first direct demonstration of LTC4S phosphorylation in whole cells.