Yu J, Wjasow C, Backer J M
Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
J Biol Chem. 1998 Nov 13;273(46):30199-203. doi: 10.1074/jbc.273.46.30199.
Our previous studies on the p85/p110alpha phosphatidylinositol 3-kinase showed that the p85 regulatory subunit inhibits the p110alpha catalytic subunit, and that phosphopeptide activation of p85/p110alpha dimers reflects a disinhibition of p110alpha (Yu, J., Zhang, Y., McIlroy, J., Rordorf-Nikolic, T., Orr, G. A., and Backer, J. M. (1998) Mol. Cell. Biol. 18, 1379-1387). We now define the domains of p85 required for inhibition of p110alpha. The iSH2 domain of p85 is sufficient to bind p110alpha but does not inhibit it. Inhibition of p110alpha requires the presence of the nSH2 domain linked to the iSH2 domain. Phosphopeptides increase the activity of nSH2/iSH2-p110alpha dimers, demonstrating that the nSH2 domain mediates both inhibition of p110alpha and disinhibition by phosphopeptides. In contrast, phosphopeptides did not increase the activity of iSH2/cSH2-p110alpha dimers, or dimers composed of p110alpha and an nSH2/iSH2/cSH2 construct containing a mutant nSH2 domain. Phosphopeptide binding to the cSH2 domain increased p110alpha activity only in the context of an intact p85 containing both the nSH2 domain and residues 1-322 (the SH3, proline-rich and breakpoint cluster region-homolgy domains). These data suggest that the nSH2 domain of p85 is a direct regulator of p110alpha activity. Regulation of p110alpha by phosphopeptide binding to the cSH2 domain occurs by a mechanism that requires the additional presence of the nSH2 domain and residues 1-322 of p85.
我们之前对p85/p110α磷脂酰肌醇3激酶的研究表明，p85调节亚基会抑制p110α催化亚基，并且p85/p110α二聚体的磷酸肽激活反映了对p110α的去抑制作用（于杰、张宇、麦基尔罗伊、罗德多夫-尼科利奇、奥尔、贝克尔（1998年），《分子细胞生物学》18卷，第1379 - 1387页）。我们现在确定了抑制p110α所需的p85结构域。p85的iSH2结构域足以结合p110α，但不会抑制它。抑制p110α需要与iSH2结构域相连的nSH2结构域的存在。磷酸肽会增加nSH2/iSH2 - p110α二聚体的活性，表明nSH2结构域介导了对p110α的抑制作用以及磷酸肽的去抑制作用。相比之下，磷酸肽不会增加iSH2/cSH2 - p110α二聚体或由p110α和包含突变nSH2结构域的nSH2/iSH2/cSH2构建体组成的二聚体的活性。磷酸肽与cSH2结构域的结合仅在含有nSH2结构域和1 - 322位残基（SH3、富含脯氨酸和断裂点簇区域同源结构域）的完整p85的情况下才会增加p110α的活性。这些数据表明，p85的nSH2结构域是p110α活性的直接调节因子。通过磷酸肽与cSH2结构域结合对p110α的调节是通过一种需要p85的nSH2结构域和1 - 322位残基额外存在的机制发生的。
