Lysophosphatidylcholine is a regulator of tyrosine kinase activity and intracellular Ca²⁺ level in Jurkat T cell line

Lysophospholipids, particularly lysophosphatidylcholine (lyso-PC), have been implicated in modulating T cell functions at the sites of inflammation and atherosclerosis. Although the chemotactic and immunomodulatory effects are well documented, the exact signaling pathway of lyso-PC action is poorly defined. In this work, we studied the earliest biochemical events in T cells triggered by lyso-PC. A marked and immediate tyrosine phosphorylation was induced in the leukemic T cell line, Jurkat. Phosphorylation of cellular substrates included src family kinase, p56^lck and syk family kinase, ZAP70. The lyso-PC induced tyrosine phosphorylation was largely dependent on the presence of functional p56^lck. Tyrosine phosphorylation was followed by the elevation of intracellular Ca²⁺ concentration. The magnitude of the mobilization of the intracellular Ca²⁺ was similar in the absence of the p56^lck activity in JCaM1.6 cells as in Jurkat cells, however, it was slightly but reproducibly delayed compared to that in the wild type cells. Inhibition of the Ser/Thr kinases and tyrosine kinases with staurosporine and genistein, respectively, decreased the rise in the intracellular Ca ²⁺ content. Moreover, pertussis toxin completely blocked the Ca ²⁺ signal supporting the role of the G-protein coupled LPC receptor in this event.