The canonical model of agonist-stimulated phosphatidylinositol-3-OH kinase (PI3K)–Akt signalling proposes that PI3K is activated at the plasma membrane, where receptors are activated and phosphatidylinositol-4,5-bisphosphate is concentrated. Here we show that phosphatidylinositol-3,4,5-trisphosphate generation and activated Akt are instead largely confined to intracellular membranes upon receptor tyrosine kinase activation. Microtubule-associated protein 4 (MAP4) interacts with and controls localization of membrane vesicle-associated PI3Kα to microtubules. The microtubule-binding domain of MAP4 binds directly to the C2 domain of the p110α catalytic subunit. MAP4 controls the interaction of PI3Kα with activated receptors at endosomal compartments along microtubules. Loss of MAP4 results in the loss of PI3Kα targeting and loss of PI3K–Akt signalling downstream of multiple agonists. The MAP4–PI3Kα assembly defines a mechanism for spatial control of agonist-stimulated PI3K–Akt signalling at internal membrane compartments linked to the microtubule network.

激动剂刺激的磷脂酰肌醇 3-OH 激酶 (PI3K)–Akt 信号传导的典型模型表明 PI3K 在质膜上被激活，在那里受体被激活并且磷脂酰肌醇 4,5-二磷酸被浓缩。在这里，我们表明，在受体酪氨酸激酶激活后，磷脂酰肌醇-3,4,5-三磷酸生成和激活的 Akt 主要限于细胞内膜。微管相关蛋白 4 (MAP4) 与膜囊泡相关 PI3Kα 相互作用并控制其定位到微管。MAP4 的微管结合域直接与 p110α 催化亚基的 C2 域结合。MAP4 控制 PI3Kα 与沿微管的内体区室中活化受体的相互作用。MAP4 的缺失导致 PI3Kα 靶向的缺失和多种激动剂下游 PI3K-Akt 信号的缺失。MAP4-PI3Kα 组件定义了一种在与微管网络相连的内膜隔室中对激动剂刺激的 PI3K-Akt 信号进行空间控制的机制。