Geering Barbara, Cutillas Pedro R, Nock Gemma, Gharbi Severine I, Vanhaesebroeck Bart
Ludwig Institute for Cancer Research, 91 Riding House Street, London W1W 7BS, United Kingdom.
Proc Natl Acad Sci U S A. 2007 May 8;104(19):7809-14. doi: 10.1073/pnas.0700373104. Epub 2007 Apr 30.
Class IA phosphoinositide 3-kinases (PI3Ks) signal downstream of tyrosine kinases and Ras and control a wide variety of biological responses. In mammals, these heterodimeric PI3Ks consist of a p110 catalytic subunit (p110alpha, p110beta, or p110delta) bound to any of five distinct regulatory subunits (p85alpha, p85beta, p55gamma, p55alpha, and p50alpha, collectively referred to as "p85s"). The relative expression levels of p85 and p110 have been invoked to explain key features of PI3K signaling. For example, free (i.e., non-p110-bound) p85alpha has been proposed to negatively regulate PI3K signaling by competition with p85/p110 for recruitment to phosphotyrosine docking sites. Using affinity and ion exchange chromatography and quantitative mass spectrometry, we demonstrate that the p85 and p110 subunits are present in equimolar amounts in mammalian cell lines and tissues. No evidence for free p85 or p110 subunits could be obtained. Cell lines contain 10,000-15,000 p85/p110 complexes per cell, with p110beta and p110delta being the most prevalent catalytic subunits in nonleukocytes and leukocytes, respectively. These results argue against a role of free p85 in PI3K signaling and provide insights into the nonredundant functions of the different class IA PI3K isoforms.
IA类磷酸肌醇3激酶（PI3K）在酪氨酸激酶和Ras的下游发出信号，并控制多种生物学反应。在哺乳动物中，这些异二聚体PI3K由与五个不同调节亚基（p85α、p85β、p55γ、p55α和p50α，统称为“p85”）中的任何一个结合的p110催化亚基（p110α、p110β或p110δ）组成。p85和p110的相对表达水平已被用来解释PI3K信号传导的关键特征。例如，游离的（即未与p110结合的）p85α已被提出通过与p85/p110竞争募集到磷酸酪氨酸对接位点来负调节PI3K信号传导。使用亲和色谱、离子交换色谱和定量质谱分析，我们证明p85和p110亚基在哺乳动物细胞系和组织中以等摩尔量存在。未获得游离p85或p110亚基的证据。每个细胞系每个细胞含有10000 - 15000个p85/p110复合物，其中p110β和p110δ分别是非白细胞和白细胞中最普遍的催化亚基。这些结果反驳了游离p85在PI3K信号传导中的作用，并为不同IA类PI3K异构体的非冗余功能提供了见解。
