A Study on an Intracellular Signaling Molecule, Phosphinositide 3-Kinase

研究了刺激GTP结合蛋白偶联受体激活细胞内磷脂酰肌醇3-激酶(PI-3-K)的机制。众所周知，胰岛素或生长因子受体的刺激通过产生与p85/p110亚型相关的酪氨酸磷酸化多肽来激活PI3-激酶。然而，在经fMLP刺激的中性粒细胞中没有发现这样的酪氨酸磷酸化蛋白，尽管可以观察到PI3-激酶的产物PIP_3在细胞中显著积聚。在本研究开始时，我们发现PI3-激酶活性的发生不受酪氨酸磷酸化蛋白的影响，但受到GTP结合蛋白的β亚基(Gbetagamma)的刺激。其他小组也得到了类似的结果，最近克隆了对Gbetagamma敏感的PI3-激酶的一个亚型(p110-Gamma)。这些研究似乎表明，GTP结合蛋白和酪氨酸激酶相互独立地发挥作用，并刺激不同亚型的PI3-激酶。然而，我们后来发现，胰岛素和fMLP共同刺激细胞会导致PIP_3的协同积聚。我们还发现，在无细胞系统中，PI3-激酶的出现可以被酪氨酸磷酸化肽和Gbetagamma协同激活。我们现在正在研究这种新型调控的生理作用。

The mechanism by which stimulation of GTP-binding protein-coupled receptors activates cellular phosphoinositide 3-kinase (PI 3-kinase) was examined. It is known that stimulation of insulin or growth factor receptors activates PI 3-kinase by producing tyrosine-phosphorylated peptide that associates with and stimulates the p85/p110 subtype of the enzyme. However, such a tyrosine-phosphorylated protein can not be found in the neutrophils stimulated by fMLP,in spite that a marked accumulation of PIP_3, a product of PI 3-kinase, can be observed in the cells. At the beginning of this study, we found the occurrence of PI 3 -kinase activity that is unaffected by tyrosine-phosphorylated proteins but is stimulated by betagamma subunits of GTP-binding proteins (Gbetagamma). Similar results were obtained by other groups and more recently one subtype of Gbetagamma-sensitive PI 3-kinase (p110gamma) was cloned. These studies seemed to indicate that GTP-binding proteins and tyrosine kinases act independently and stimulate the different subtypes of PI 3-kinase. We found later, however, that co-stimulation of cells with insulin and fMLP causes synergistic accumulation of PIP_3. We also found in cell-free systems the occurrence of PI 3-kinase that can be synergistically activated by tyrosine-phosphorylated peptide and Gbetagamma. We are now examining for a physiological role of this novel type of regulation.