Chemical Proteomics of the Tumor Suppressor Fhit Covalently Bound to the Cofactor Ap3A Elucidates Its Inhibitory Action on Translation

The tumor suppressor protein fragile histidine triad (Fhit) is known to be associated with genomic instability and apoptosis. The tumor-suppressive function of Fhit depends on the interaction with the alarmone diadenosine triphosphate (Ap3A), a noncanonical nucleotide whose concentration increases upon cellular stress. How the Fhit–Ap3A complex exerts its signaling function is unknown. Here, guided by a chemical proteomics approach employing a synthetic stable Fhit–Ap3A complex, we found that the Fhit–Ap3A complex, but not Fhit or Ap3A alone, impedes translation. Our findings provide a mechanistic model in which Fhit translocates from the nucleolus into the cytosol upon stress to form an Fhit–Ap3A complex. The Fhit–Ap3A complex impedes translation both in vitro and in vivo, resulting in reduced cell viability. Overall, our findings provide a mechanistic model by which the tumor suppressor Fhit collaborates with the alarmone Ap3A to regulate cellular proliferation.肿瘤抑制蛋白脆性组氨酸三联体（fragile histidine triad, Fhit）已被证实与基因组不稳定性及细胞凋亡相关。Fhit的抑癌功能依赖于与警报素二腺苷三磷酸（diadenosine triphosphate, Ap3A）的相互作用——Ap3A是一种非经典核苷酸，其浓度会在细胞应激状态下升高。目前学界尚未明确Fhit-Ap3A复合物如何发挥其信号传导功能。本研究采用基于合成稳定Fhit-Ap3A复合物的化学蛋白质组学方法开展实验，发现Fhit-Ap3A复合物（而非单独的Fhit或Ap3A）可抑制蛋白质翻译。我们的研究提出了一套机制模型：当细胞受到应激时，Fhit会从核仁转位至细胞质基质，进而形成Fhit-Ap3A复合物；该复合物可在体外及体内均抑制蛋白质翻译，最终导致细胞活力降低。综上，本研究阐明了肿瘤抑制蛋白Fhit与警报素Ap3A协同调控细胞增殖的分子机制。