Coordination between the eIF2 kinase GCN2 and p53 signaling supports purine metabolism and the progression of prostate cancer

Cancers invoke various pathways to mitigate external and internal stresses to continue their growth and progression. We previously reported that the eIF2 kinase GCN2 and the integrated stress response are constitutively active in prostate cancer (PCa) and are required to maintain amino acid homeostasis needed to fuel tumor growth. However, although loss of GCN2 function reduces intracellular amino acid availability and PCa growth, there is no appreciable cell death. Here, we discovered that the loss of GCN2 in PCa induces prosenescent p53 signaling. This p53 activation occurred through GCN2 inhibition-dependent reductions in purine nucleotides that impaired ribosome biogenesis and, consequently, induced the impaired ribosome biogenesis checkpoint. p53 signaling induced cell cycle arrest and senescence that promoted the survival of GCN2-deficient PCa cells. Depletion of GCN2 combined with loss of p53 or pharmacological inhibition of de novo purine biosynthesis reduced proliferation and enhanced cell death in PCa cell lines, organoids, and xenograft models. Our findings highlight the coordinated interplay between GCN2 and p53 regulation during nutrient stress and provide insight into how they could be targeted in developing new therapeutic strategies for PCa. Overall design: To investigate how loss of p53 in combination with GCN2 inhibition affects gene expression in the human prostate cancer cell line LNCaP. We performed RNA-seq on wild-type (WT) and p53 KO LNCaP cells treated with the GCN2 inhibitor GCN2iB.

肿瘤可激活多条通路以抵御内外源性应激，从而维持其生长与进展。我们此前报道，eIF2激酶GCN2与整合应激反应（integrated stress response）在前列腺癌（prostate cancer, PCa）中呈组成型激活，且是维持肿瘤生长所需氨基酸稳态的必要条件。然而，尽管GCN2功能缺失会降低细胞内氨基酸可用性并抑制PCa生长，但并未引发明显的细胞死亡。本研究发现，PCa中GCN2缺失可诱导促衰老型p53信号通路激活。该p53激活通过GCN2抑制依赖的嘌呤核苷酸（purine nucleotides）水平降低实现：嘌呤核苷酸减少会损害核糖体生物发生（ribosome biogenesis），进而激活受损核糖体生物发生检查点（impaired ribosome biogenesis checkpoint）。p53信号通路可诱导细胞周期阻滞与细胞衰老，从而维持GCN2缺陷型PCa细胞的存活。联合敲除GCN2与p53，或通过药理学手段抑制嘌呤从头合成（de novo purine biosynthesis）通路，可在PCa细胞系、类器官及异种移植模型中降低细胞增殖并增强细胞死亡。本研究结果揭示了营养应激状态下GCN2与p53调控通路间的协同互作关系，并为靶向二者开发PCa新型治疗策略提供了理论依据。研究设计：为探究联合敲除p53与GCN2抑制对人前列腺癌细胞系LNCaP中基因表达的影响，本研究对经GCN2抑制剂GCN2iB处理的野生型（wild-type, WT）及p53敲除（p53 knockout, KO）LNCaP细胞进行了RNA测序（RNA-seq）。