Measurement of Phosphatidylinositol (PI) Hydrolysis in Activated T Lymphocytes
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T-cell activation by antigen-receptor ligation results in rapid activation of phospholipase-Cγ1 (PLC). Activated PLC hydrolyzes membrane inositol phospholipids (PIP 2 ) generating two second messengers: inositol(1,4,5)tris phosphate (IP 3 ) and diacylglycerol (DG) ( 1 ). IP 3 stimulates release of intracellularly stored Ca 2+ resulting in the initial intracellular Ca 2+ peak whereas, DAG activates protein kinase C (PKC) with an accompanying shift in that enzyme from cytosol to membrane (Fig. 1 ) ( 2 – 5 ).
Fig. 1. T-cell receptor signaling begins with the ligand-receptor interaction, resulting in activation of protein tyrosine kinases that phosphorylate PLC-γ1, resulting in PIP 2 turnover, increased intracellular calcium [Ca 2+ ] i , and protein kinase C (PKC) activation. PKC and [Ca 2+ ] i , participate in the regulation of interleukin 2 (IL-2) gene transcription and IL-2 receptor gene transcription in T cells ( 5 , 6 ).
