Biomedical subjects

Toru Hirota

Publications and source records attributed to Toru Hirota.

21 records · Page 2Linked to original sources

PubMed2003

CENP-A phosphorylation by Aurora-A in prophase is required for enrichment of Aurora-B at inner centromeres and for kinetochore function.

The Aurora (Ipl1)-related kinases are universal regulators of mitosis. We now show that Aurora-A, in addition to Aurora-B, regulates kinetochore function in human cells. A two-hybrid screen identified the kinetochore component CENP-A as a protein that interacts with Aurora-A. Aurora-A phosphorylated CENP-A in vitro on Ser-7, a residue also known to be targeted by Aurora-B. Depletion of Aurora-A or Aurora-B by RNA interference revealed that CENP-A is initially phosphorylated in prophase in a manner dependent on Aurora-A, and that this reaction appears to be required for the subsequent Aurora-B-dependent phosphorylation of CENP-A as well as for the restriction of Aurora-B to the inner centromere in prometaphase. Prevention of CENP-A phosphorylation also led to chromosome misalignment during mitosis as a result of a defect in kinetochore attachment to microtubules. Our observations suggest that phosphorylation of CENP-A on Ser-7 by Aurora-A in prophase is essential for kinetochore function.

Amino Acid Sequence↗

PubMed2002

WARTS tumor suppressor is phosphorylated by Cdc2/cyclin B at spindle poles during mitosis.

Identification of physiological substrates for Cdc2/cyclin B is crucial for understanding the functional link between mitotic events and Cdc2/cyclin B activation. A human homologue of the Drosophila warts tumor suppressor, termed WARTS, is a serine/threonine kinase and a dynamic component of the mitotic apparatus. We have found that Cdc2/cyclin B forms a complex with a fraction of WARTS in the centrosome and phosphorylates the Ser613 site of WARTS during mitosis. Immunocytochemical analysis has shown that the S613-phosphorylated WARTS appears in the spindle poles at prometaphase and disappears at telophase. Our findings suggest that Cdc/cyclin B regulates functions of WARTS on the mitotic apparatus.

Amino Acid Sequence↗

PubMed2002

Roles of aurora-A kinase in mitotic entry and G2 checkpoint in mammalian cells.

BACKGROUND: Various mitotic events are controlled by Cdc2-cyclin B and other mitotic kinases. Aurora/Ipl1-related mitotic kinases were proved to play key roles in mitotic progression in diverse lower organisms. Aurora-A is a mammalian counterpart of aurora/Ipl1-related kinases and is thought to be a potential oncogene. However, the regulation of aurora-A activation and the commitment of aurora-A in the progression of G2-M phase are largely unknown in mammalian cells. RESULTS: We demonstrated that aurora-A is activated depending on the activation of Cdc2-cyclin B in mammalian cells. Since Cdc2-cyclin B does not directly phosphorylate aurora-A, indirect pathways such as the inhibition of PP1 by Cdc2-cyclin B may act for the activation of aurora-A kinase. Microinjection of anti-aurora-A antibodies into HeLa cells at late G2 phase caused a significant delay in mitotic entry. Furthermore, aurora-A activation at G2-M transition was inhibited by DNA damage, and the over-expression of aurora-A induced the abrogation of the DNA damage-induced G2 checkpoint. CONCLUSIONS: Aurora-A is activated downstream of Cdc2-cyclin B and plays crucial roles in proper mitotic entry and G2 checkpoint control. Dysregulation of aurora-A induces abnormal G2-M transition in mammalian cells and may lead to chromosome instability, which results in the development and progression of malignant tumours.

Animals↗