Analysis of serine protease Omi-mediated-signaling pathway which could affect both tumorigenesis and neurodegenerative disorder

众所周知，细胞凋亡是肿瘤发生的重要保障。丝氨酸蛋白酶Omi最初被认为是一种促凋亡分子。然而，最近的研究表明，Omi蛋白酶活性的丧失增加了应激诱导的细胞死亡的易感性，从而导致神经退行性疾病。这些复杂的发现表明，OMI的蛋白酶活性不仅参与了细胞的凋亡，而且还参与了细胞的稳态。然而，OMI用来介导这一新过程的靶点尚不清楚。以前，我们发现WARTS(WTS)/Lats1有丝分裂激酶与Omi的PDZ结构域相互作用，并促进其蛋白酶活性。我们现在报道WTS是Omi酶活性的底物，因此它不仅是该酶的调节因子，也是该酶的下游靶标。WTS需要与Omi PDZ结构域相互作用才能被蛋白降解。当caspase-9基因缺陷的小鼠胚胎成纤维细胞(MEF)用星形孢子素处理时，WTS被激活的内源性Omi蛋白降解，而不诱导细胞死亡，因此，WTS的蛋白水解酶活性并不一定是细胞死亡的必要条件。我们发现，尽管有丝分裂的持续时间没有显着变化，但HeLa细胞中OMi的缺失会导致细胞增殖加速。WTS的耗竭对S期的进展也有同样的影响。因此，OMI产生的WTS蛋白水解性片段(S)可能是G1/S进程的抑制因子。我们的数据揭示了Omi介导的WTS在间期对细胞周期进程的负调控中的作用，表明Omi除了凋亡之外还有另一种新的功能。

It is well known that apoptosis is a major safeguard to tumorigenesis. The serine protease Omi was initially regarded as a proapoptotic molecule. Recent studies, however, indicate that loss of Omi protease activity increases susceptibility to stress-induced cell death, resulting neurodegenerative disorder. These complicated findings suggest that protease activity of Omi is involved not only in apoptosis but also in cellular homeostasis. However, the targets which Omi uses to mediate this novel process are unknown. Previously, we showed that WARTS (WTS)/Lats1 mitotic kinase interacts with the PDZ domain of Omi and promotes its protease activity. We now report that WTS is a substrate for Omi protease activity, thus it is not only a regulator but also a downstream target of this protease. Interaction with Omi PDZ domain is required for WTS to be proteolysed. When caspase-9-deficient mouse embryonic fibroblasts (MEFs) were treated with staurosporine, WTS was proteolysed by activated endogenous Omi without induction of cell death Therefore, protease activity of Omi and proteolysis of WTS are not necessarily required for cell death. We found that depletion of Omi from HeLa cells results in accelerated cell proliferation despite no significant change in the duration of mitosis. The depletion of WTS showed the same effect on S phase progression. Therefore, WTS proteolytic fragment(s) generated by Omi may act as an inhibitor of G1/S progression. Our data reveal a role for Omi-mediated processing of WTS in negative regulation of cell cycle progression at interphase, suggesting a novel function of Omi other than apoptosis.