title: Serine protease Omi/HtrA2 targets WARTS kinase to control cell proliferation.
abstract: The serine protease Omi/HtrA2 was initially regarded as a proapoptotic molecule that proteolyses several proteins to induce cell death. Recent studies, however, indicate that loss of Omi protease activity increases susceptibility to stress-induced cell death. These complicated findings suggest that the 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)/large tumor-suppressor 1 mitotic kinase interacts with the protein/discs-large protein/zonula (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.
authors.affiliation: Department of Tumor Genetics and Biology, Graduate School of Medical Sciences, Kumamoto University, Honjo, Kumamoto, Japan. hsaya@gpo.kumamoto-u.ac.jp
authors.forename: S
authors.initials: S
authors.lastname: Kuninaka
authors.forename: S-I
authors.initials: SI
authors.lastname: Iida
authors.forename: T
authors.initials: T
authors.lastname: Hara
authors.forename: M
authors.initials: M
authors.lastname: Nomura
authors.forename: H
authors.initials: H
authors.lastname: Naoe
authors.forename: T
authors.initials: T
authors.lastname: Morisaki
authors.forename: M
authors.initials: M
authors.lastname: Nitta
authors.forename: Y
authors.initials: Y
authors.lastname: Arima
authors.forename: T
authors.initials: T
authors.lastname: Mimori
authors.forename: S
authors.initials: S
authors.lastname: Yonehara
authors.forename: H
authors.initials: H
authors.lastname: Saya
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000502:physiology; D019556:COS Cells; D049109:Cell Proliferation; D002522:Chlorocebus aethiops; D006367:HeLa Cells; D000074923:High-Temperature Requirement A Serine Peptidase 2; D006801:Humans; D007399:Interphase / Q000502:physiology; D024101:Mitochondrial Proteins / Q000502:physiology*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D012697:Serine Endopeptidases / Q000502:physiology*; D013379:Substrate Specificity
chemical_list: D024101:Mitochondrial Proteins; C092745:LATS1 protein, human; D017346:Protein Serine-Threonine Kinases; D012697:Serine Endopeptidases; C000615914:HTRA2 protein, human; D000074923:High-Temperature Requirement A Serine Peptidase 2; C000615915:Htra2 protein, mouse