Co-regulation of p53 and PD-L1 by the VPRBP-USP2 axis in transcription and ubiquitylation

尽管p53在几乎50%的人类癌症中频繁突变，但许多人类肿瘤 保留野生型p53，但其活性通过多种机制下调。比如说， Mdm 2是p53的一个关键阻遏物，作为一种主要的E3连接酶，用于泛素化介导的 降解Mdm 2的抑制被广泛接受为用于治疗人类肿瘤的经验证的方法。 通过重新激活p53肿瘤抑制功能保留野生型p53的癌症。然而，尽管如此， 尽管在开发高效的Mdm 2抑制剂方面进行了大量的努力，但是它们中没有一个被 由于这些抑制剂在体内的毒性，被批准在治疗上非常有效。到 克服这一重大问题，有必要通过思考“开箱即用”来寻找候选人。 战略在本申请中，我们将VPRBP-USP 2轴确定为这样的候选轴。像Mdm 2一样， VPRBP可以通过转录抑制和泛素化介导抑制p53的功能。 降解有趣的是，与Mdm 2不同，VPRBP充当PD-L1的主调节因子。 USP 2严格控制VPRBP的稳定性。已显示阻断PD-L1/PD-1通路 在癌症患者中具有显著的抗肿瘤作用。有趣的是，临床研究表明， 通过抗PD 1或抗PD-L1抗体成功阻断PD 1-PD-L1具有正相关性 PD-L1在肿瘤细胞中的表达水平。因此，尽管高水平的PD-L1阻止了细胞毒性， T细胞有效地靶向肿瘤细胞，它显然也作为一个潜在的选择性标记 用于PD 1-PD-L1阻断治疗的患者分层。引人注目的是，我们的初步研究表明， 将VPRBP敲低/或USP 2抑制剂与抗PD-1抗体治疗组合， 在携带肿瘤的免疫功能正常的小鼠中显著增强肿瘤生长抑制 表达野生型p53。值得注意的是，与Mdm 2不同，USP 2基因的敲除没有明显的影响 对正常组织中的正常发育或细胞活力的影响。这些数据表明，USP 2是一种 激活p53介导的人肿瘤抑制作用的有希望的治疗靶点 癌症而不会对正常组织造成严重毒性。因此，解剖 VPRBP-USP 2轴在人类癌症中调节p53和PD-L1的精确机制 并为潜在的癌症治疗提供重要见解。在Aim 1中，我们将阐明 VPRBP/USP 2轴通过转录抑制调节p53和PD-L1的机制 和泛素化途径。在目标2中，将检查USP 2抑制剂的组合是否 (or VPRBP敲低）与抗PD-1治疗能够显著改善在抗PD-1治疗中的功效。 p53介导的体内肿瘤生长抑制通过无原因触发抗肿瘤免疫 严重毒性。

Although p53 is frequently mutated in almost 50% of human cancers, many human tumors retain wild-type p53 but its activities are downregulated through multiple mechanisms. For example, Mdm2 is a key repressor of p53 by acting as a major E3 ligase for ubiquitylation-mediated degradation. Inhibition of Mdm2 is well accepted as a validated approach for the treatment of human cancers retaining wild-type p53 by reactivating the p53 tumor suppressor function. Nevertheless, despite of intense efforts in developing highly potent Mdm2 inhibitors, none of them has been approved therapeutically very effective because of the toxicity of these inhibitors in vivo. To overcoming this major issue, it is necessary to search for a candidate by thinking about a ‘out of box’ strategy. In this application, we identify the VPRBP-USP2 axis as such a candidate. Like Mdm2, VPRBP can suppress p53 function by both transcriptional repression and ubiquitylation-mediated degradation. Interestingly, unlike Mdm2, VPRBP acts as a master regulator of PD-L1.Moreover, the stability of VPRBP is tightly control by USP2. Blocking the PD-L1/PD-1 pathway has been shown remarkable anti-tumor effects in cancer patients. Interestingly, clinical studies demonstrated that the success of PD1–PD-L1 blockade by either anti-PD1 or anti-PD-L1 antibody has a positive correlation with PD-L1 expression levels in tumor cells. Thus, although high levels of PD-L1 prevents cytotoxic T cells from effectively targeting tumor cells, it apparently also serves as a potential selective marker for patient stratification for PD1–PD-L1 blockade therapy. Strikingly, our preliminary studies showed that combining VPRBP knockdown/or USP2 inhibitors with an anti-PD-1 antibody treatment dramatically enhanced tumor growth suppression in the immune-proficient mice bearing the tumors expressing wild type p53. Notably, unlike Mdm2, knockout of the USP2 gene has no obvious effect on normal development or cell viability in normal tissues. These data suggest that USP2 is a promising therapeutic target for activating p53-mediated tumor suppressive effects in human cancers without causing severe toxicity to normal tissues. Thus, it is very important to dissect the precise mechanism of the VPRBP-USP2 axis in regulating both p53 and PD-L1 in human cancers and provide critical insights into potential cancer treatment. In Aim1, we will elucidate the molecular mechanism of the VPRBP/USP2 axis in regulating p53 and PD-L1 through transcription repression and the ubiquitylation pathway. In Aim 2, will examine whether the combination of USP2 inhibitors (or VPRBP knockdown) with the anti-PD-1 treatment is able to significantly improve the efficacy in p53-mediated tumor growth suppression in vivo by triggering anti-tumor immunity without cause severe toxicity.