Biochemical and functional investigation of the novel enzymatic activities of MESH1

细菌科普代谢应激的主要策略是通过由alarmone（p）ppGpp的积累触发的严格响应。虽然后生动物基因组也编码（p）ppGpp水解酶SpoT（MESH 1）的同源物，但在后生动物中既没有发现（p）ppGpp合成酶的同源物，也没有发现（p）ppGpp本身。因此，严格的反应被认为是不存在的后生动物。出乎意料的是，我们发现哺乳动物细胞中MESH 1的沉默引发了与细菌严格反应高度相似的细胞反应。这种反应的特点是短期的压力生存，可逆的增殖停滞以及广泛的转录和代谢重编程。由于在后生动物中未发现（p）ppGpp，我们假设Mesh 1通过独立于（p）ppGpp的机制介导新的细胞反应。在这个提议中，我们将研究MESH 1的新酶活性的生物化学，并建立它们对哺乳动物细胞对各种应激和刺激的反应的功能贡献。拟议的研究的成功执行将有助于阐明MESH 1的新的酶活性-细菌（p）ppGpp水解酶的哺乳动物直向同源物-有助于其在介导哺乳动物细胞对各种应激和刺激的反应中的生物学功能，并实现其在人类疾病中的治疗潜力。

The main strategy for bacteria to cope with metabolic stresses is through the stringent response triggered by the accumulation of the alarmone (p)ppGpp. While metazoan genomes also encode a homologue of the (p)ppGpp hydrolase SpoT (MESH1), neither a homologue of the (p)ppGpp synthetase nor (p)ppGpp itself has been found in metazoa. Therefore, the stringent response was thought to be absent in metazoa. Unexpectedly, we found that the silencing of MESH1 in mammalian cells triggered a cellular response highly similar to the bacterial stringent response. Such a response is characterized by the short-term stress survival, reversible proliferation arrest as well as extensive transcriptional and metabolic reprogramming. As (p)ppGpp is not found in metazoa, we hypothesize that Mesh1 mediates the novel cellular response by mechanisms independent of (p)ppGpp. In this proposal, we will investigate the biochemistry of the novel enzymatic activities of MESH1 and establish their functional contributions to the mammalian cells’ response to various stresses and stimuli. The successful execution of the proposed studies will help elucidate how the novel enzymatic activities of MESH1—the mammalian orthologue of the bacterial (p)ppGpp hydrolase—contribute to its biological function in mediating the mammalian cellular response to various stresses and stimuli and realize its therapeutic potential in human diseases.