Breakdown of phosphatidylinositol 4,5-bisphosphate in a T-cell leukaemia line stimulated by phytohaemagglutinin is not dependent on Ca2+ mobilization

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Abstract
Addition of phytohemagglutinin (PHA) to the [32P]Pi-prelabeled JURKAT cells, a human T cell leukemia line, resulted in a decrease of [32P]phosphatidylinositol-4,5-bisphosphate [PtdIns(4,5)P2] to .apprx. 35% of the control value. The decrease was almost complete within 30 s after the PHA addition. This decrease was followed by an increase in the 32P-labeling of phosphatidic acid (maximally 2.8-fold at 2 min). The stimulation of myo-[2-3H]inositol-prelabled JURKAT cells by PHA induced an accumulation of [2-3H]inositol trisphosphate in that presence of 5 mM-LiCl. The result indicates hydrolysis of PtdIns (4,5)P2 by a phospholipase C. The PHA stimulation of JURKAT cells induced about 6-fold increase in the cytosolic free Ca2+ concentration, [Ca2+]i, which was reported by Quin-2, a fluorescent Ca2+ indicator. Studies with particularly Ca2+-depleted JURKAT cells, with the Ca2+ ionophore A23187 [calcimycin], and with 8-(diethylamino)-octyl-3,4,5-trimethoxybenzoate indicate that the breakdown of PtdIns(4,5)P2 is not mediated through chnges of [Ca2+]i. The PHA-induced breakdown of PtdIns(4,5)P2 in JURKAT cells is not dependent on the Ca2+ mobilization.