Phosphoinositide 3-kinase in rat liver nuclei.
Phosphoinositide 3-kinase in rat liver nuclei.
复制标题
大鼠肝核中的磷酸肌醇 3-激酶。
DOI：
10.1021/bi972551g
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发表时间：
1998
期刊：
影响因子：
--
通讯作者：
Chen,CS
中科院分区：
文献类型：
--
作者：
Lu,PJ;Hsu,AL;Wang,DS;Yan,HY;Yin,HL;Chen,CS
本研究的生化和免疫化学数据显示，大鼠肝细胞核中存在p85/p110磷脂酰肌醇3-激酶(PI-3-Kinase)。用[γ-32P]三磷酸腺苷孵育完整肝细胞核进行32P标记，可形成[32P]磷脂酰肌醇3，4，5-三磷酸[PtdIns(3，4，5)P3]，并伴随少量[32P]磷脂酰肌醇3-磷酸[PtdIns(3)P]。亚核部分的研究表明，等电点3-激酶并不局限于核膜。核可溶部分还含有磷脂酰肌醇3-激酶和一系列肌醇代谢酶，包括磷脂酶C(PLC)、磷脂酰肌醇磷酸酶和二酰甘油(DAG)酶。因此，磷脂酰肌醇4，5-二磷酸[PtdIns(4，5)P2]与核提取物在[γ-32P]存在下以相互依赖的方式产生一系列32P标记的D-3磷脂酰肌醇和磷脂酸(PA)。根据免疫反应性和动力学行为，核内PI3-激酶与PI3-激酶α相似，但不完全相同，约占细胞内总PI3-激酶的5%。此外，我们还验证了PtdIns(4，5)P2结合蛋白通过控制底物可获得性来部分调节核内PI3K的前提。鉴于其独特的钙依赖的PtdIns(4，5)P2结合能力，研究了核肌动蛋白调节蛋白CAPG对PI3-激酶活性的影响。体外实验数据表明，CAPG对细胞核PI3K的抑制作用是由CAPG的PKC磷酸化和[Ca~(2+)]升高引起的。这种依赖于CAPG的调节在核PLC和PI 3-激酶通路之间提供了一种可信的联系，用于交叉通讯。综上所述，这些发现为大鼠肝细胞核中存在自主的PI3-激酶循环提供了明确的数据。PI3K的核定位可能有助于更好地理解其在响应不同生理刺激时将信号从质膜传递到细胞核的功能。
Biochemical and immunochemical data from the present investigation reveal the existence of a p85/p110 phosphoinositide 3-kinase (PI 3-kinase) in rat liver nuclei.32P-Labeling of membrane phosphoinositides by incubating intact nuclei with [γ-32P]ATP results in the formation of [32P]phosphatidyl-inositol 3,4,5-trisphosphate [PtdIns(3,4,5)P3], accompanied by small quantities of [32P]phosphatidylinositol 3-phosphate [PtdIns(3)P]. Studies with subnuclear fractions indicate that the PI 3-kinase is not confined to nuclear membranes. The nuclear soluble fraction also contains PI 3-kinase and an array of inositide-metabolizing enzymes, including phospholipase C (PLC), phosphoinositide phosphatase, and diacylglycerol (DAG) kinase. As a result, exposure of phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2] to the nuclear extract in the presence of [γ-32P]ATP generates a series of32P-labeled D-3 phosphoinositides and phosphatidic acid (PA) in an interdependent manner. On the basis of the immunological reactivity and kinetic behavior, the nuclear PI 3-kinase is analogous, if not identical, to PI 3-kinase α, and constitutes about 5% of the total PI 3-kinase in the cell. Moreover, we test the premise that nuclear PI 3-kinase may, in part, be regulated through the control of substrate availability by PtdIns(4,5)P2-binding proteins. Effect of CapG, a nuclear actin-regulatory protein, on PI 3-kinase activity is examined in view of its unique Ca2+-dependent PtdIns(4,5)P2-binding capability. In vitro data show that the CapG-mediated inhibition of nuclear PI 3-kinase is prompted by PKC phosphorylation of CapG and elevated [Ca2+]. This CapG-dependent regulation provides a plausible link between nuclear PLC and PI 3-kinase pathways for cross-communications. Taken together, these findings provide definite data concerning the presence of an autonomous PI 3-kinase cycle in rat liver nuclei. The nuclear location of PI 3-kinase may lead to a better understanding regarding its functional role in transducing signals from the plasma membrane to the nucleus in response to diverse physiological stimuli.