A code of mono-phosphorylation modulates the function of RB. Sanidas et al.

Hyper-phosphorylation of RB controls its interaction with E2F and inhibits its tumor suppressor properties. However, during G1 active RB can be mono-phosphorylated on any one of 14 CDK phosphorylation sites. Here we used quantitative proteomics to profile protein complexes formed by each mono-phosphorylated RB isoform (mP-RB) and identified the associated transcriptional outputs. The results show that the 14 sites of mono-phosphorylation co-ordinate RB’s interactions and confer functional specificity. All 14 mP-RBs interact with E2F/DP proteins but they provide different shades of E2F regulation. RB mono-phosphorylation at S811, for example, alters RB transcriptional activity by promoting its association with NuRD complexes. The greatest functional differences between mP-RBs are evident beyond the cell cycle machinery. RB mono-phosphorylation at S811 or T826 stimulates the expression of oxidative phosphorylation genes, increasing cellular oxygen consumption. These results indicate that RB activation signals are integrated in a phosphorylation code that determines the diversity of RB activity.

RB蛋白的高磷酸化调控其与E2F的结合并抑制其肿瘤抑制特性。然而，在G1期，RB蛋白可在14个CDK磷酸化位点中的任何一个位点发生单磷酸化。本研究采用定量蛋白质组学技术对由每个单磷酸化RB异构体（mP-RB）形成的蛋白复合物进行表征，并确定了相关的转录输出。结果显示，14个单磷酸化位点共同调控RB的相互作用并赋予其功能特异性。所有14种mP-RB均与E2F/DP蛋白相互作用，但它们提供了不同层次的E2F调控。例如，RB蛋白在S811位点的单磷酸化通过促进其与NuRD复合物的结合，改变RB的转录活性。mP-RB之间的最大功能差异在细胞周期机制之外尤为明显。RB蛋白在S811或T826位点的单磷酸化刺激氧化磷酸化基因的表达，增加细胞氧消耗。这些结果表明，RB激活信号被整合到一个磷酸化代码中，该代码决定了RB活动的多样性。