Modulation of Phosphorylation of Tocopherol and Phosphatidylinositol by hTAP1/SEC14L2-Mediated Lipid Exchange
Figure 4
Stimulation of phosphatidylinositol-3-phosphate kinase gamma (PI3Kγ) activity with different tocopherol analogues.
(A) In vitro PI3Kγ activity is modulated by recombinant hTAP1 (4 µg) in a tocopherol analogue specific manner. PI3Kγ activity was assessed as described in materials and methods and the mean±SEM results plotted (n = 3, *P<0.05 relative to untreated control (c) without hTAP1; #P<0.05 relative to αT in the presence of hTAP1). αT, βT, γT, δT: α-, β-, γ-, δ-tocopherols, respectively. W: wortmannin. (B) In vitro PI3Kγ activity is inhibited by wortmannin (W) (1 µM), and stimulated by αT (50 µM) and more by αTP (50 µM). Recombinant hTAP1 (4 µg) inhibits PI3Kγ activity possibly by forming a stalled/inactive complex; addition of αT or αTP reverts the inhibition by hTAP1, possibly by promoting dissociation of the inactive complex and/or competing with bound phosphatidylinositol allowing its egress from the hTAP1 binding site and the transfer to the enzyme. PI3Kγ activity was assessed as described in materials and methods, the control set to 100% and the mean±SEM plotted (n = 3, *P<0.05 relative to control (c)).