The yeast and mammalian isoforms of phosphatidylinositol transfer protein can all restore phospholipase C-mediated inositol lipid signaling in cytosol-depleted RBL-2H3 and HL-60 cells

The mammalian phosphatidylinositol transfer proteins (PITP) and the yeast Saccharomyces cerevisiae PITP (SEC14p) that show no sequence homology both catalyze exchange of phosphatidylinositol (PI) between membranes compartments in vitro. In HL-60 cells where the cytosolic proteins are depleted by permeabilization, exogenously added PITP alpha is required to restore G protein-mediated phospholipase C beta (PLC beta) signaling, Recently, a second mammalian PITP beta form has been described that shows 77% identity to rat PITP alpha, We have examined the ability of the two mammalian PITPs and SEC14p to restore PLC-mediated signaling in cytosol-depleted HL-60 and RBL-2H3 cells. Both PITP alpha and PITP beta isoforms as well as SEC14p restore G protein-mediated PLC beta signaling with a similar potency, In RBL-2H3 cells, crosslinking of the IgE receptor by antigen stimulates inositol lipid hydrolysis by tyrosine phosphorylation of PLC gamma 1, Permeabilization of RBL cells leads to loss of PLC gamma 1 as well as PITP into the extracellular medium and this coincides with loss of antigen-stimulated lipid hydrolysis. Both PLC gamma 1 and PITP were required to restore inositol lipid signaling, We conclude that (i) because the PI binding/transfer activities of PITP/SEC14p is the common feature shared by all three transfer proteins, it must be the relevant activity that determines their abilities to restore inositol lipid-mediated signaling and (ii) PITP is a general requirement for inositol lipid hydrolysis regardless of how and which isoform of PLC is activated by the appropriate agonist.