Kozawa O, Blume-Jensen P, Heldin C H, Rönnstrand L
Ludwig Institute for Cancer Research, Uppsala Branch, Biomedical Centre, Sweden.
Eur J Biochem. 1997 Aug 15;248(1):149-55. doi: 10.1111/j.1432-1033.1997.00149.x.
We have shown previously that the stem cell factor (SCF) receptor undergoes phosphorylation on serine residues following ligand stimulation, and that this phopshorylation is dependent mainly on the activity of protein kinase C (PKC). In the present study, we have further investigated the molecular mechanisms behind SCF-stimulated activation of PKC, and found that SCF does not activate phosphatidylinositol-specific phospholipase C. In contrast, phospholipase D (PLD) is activated in response to SCF in a dose-dependent manner. Activation of PLD was not inhibited by calphostin C, an inhibitor of PKC. On the other hand, inhibitors of phosphatidylinositol PtdIns 3'-kinase (PtdIns 3'-kinase), i.e. wortmannin and LY294002, inhibited SCF-induced PLD activation. Moreover, a mutant SCF receptor in which Tyr721, which is responsible for activation of PtdIns 3'-kinase, is mutated to a phenylalanine residue was unable to mediate activation of PLD. Thus, PtdIns 3'-kinase appears to be essential for SCF-induced PLD activation. Furthermore, we demonstrate that phosphatidic acid (PtdH), generated through the action of PLD in response to SCF, is metabolized to diacylglycerol by dephosphorylation. Diacylglycerol can then activate PKC, and, moreover, after deacylation by a diacylglycerol lipase, yield arachidonic acid, an important second messenger in cell signaling.
我们之前已经表明，干细胞因子（SCF）受体在配体刺激后丝氨酸残基会发生磷酸化，并且这种磷酸化主要依赖于蛋白激酶C（PKC）的活性。在本研究中，我们进一步研究了SCF刺激PKC激活背后的分子机制，发现SCF不会激活磷脂酰肌醇特异性磷脂酶C。相反，磷脂酶D（PLD）会以剂量依赖的方式响应SCF而被激活。PLD的激活不受PKC抑制剂钙泊三醇C的抑制。另一方面，磷脂酰肌醇3'-激酶（PtdIns 3'-激酶）的抑制剂，即渥曼青霉素和LY294002，抑制了SCF诱导的PLD激活。此外，一个将负责激活PtdIns 3'-激酶的Tyr721突变为苯丙氨酸残基的突变型SCF受体无法介导PLD的激活。因此，PtdIns 3'-激酶似乎是SCF诱导PLD激活所必需的。此外，我们证明，通过PLD响应SCF的作用而产生的磷脂酸（PtdH）通过去磷酸化代谢为二酰基甘油。二酰基甘油随后可以激活PKC，而且，在被二酰基甘油脂肪酶去酰化后，产生花生四烯酸，这是细胞信号传导中的一种重要第二信使。
