Cell Cycle-dependent Expression and Spindle Pole Localization of a Novel Human Protein Kinase, Aik, Related to Aurora of Drosophila and Yeast Ipl1

doi:10.1074/jbc.272.21.13766

Cell Cycle-dependent Expression and Spindle Pole Localization of a Novel Human Protein Kinase, Aik, Related to Aurora of Drosophila and Yeast Ipl1*

From the Department of Molecular Pathobiochemistry, Gifu University School of Medicine, Tsukasamachi-40, Gifu 500 and the^‡Tsukuba Life Science Center, The Institute of Physical and Chemical Research (RIKEN), 3-1-1 Koyadai, Tsukuba, Ibaraki 305, Japan

Abstract

Mutations in Aurora of Drosophila and related Saccharomyces cerevisiae Ipl1 kinase are known to cause abnormal chromosome segregation. We have isolated a cDNA encoding a novel human protein kinase of 402 amino acids with a predicted molecular mass of 45.9 kDa, which shares high amino acid identities with the Aurora/Ipl1 protein kinase family; hence the cDNA is designated as aik(aurora/IPL1-related kinase). Amino acid sequence of C-terminal kinase domain of Aik shares 86, 86, 72, 59, and 49% identity with those of Xenopus XLP46APK and XLP46BPK, mouse STK-1, Aurora of Drosophila, and yeast Ipl1, respectively, whereas N-terminal domain of Aik shares high homology only with those of XLP46APK and XLP46BPK. Northern and Western blotting analyses revealed that Aik is expressed highly in testis and various proliferating cells including HeLa cells. In HeLa cells, the endogenous levels of aik mRNA and protein contents are tightly regulated during cell cycle progression. Both of these levels are low in G₁/S, accumulate during G₂/M, and reduce rapidly after mitosis. Its protein kinase activity is also enhanced at mitosis as inferred by exogenous casein phosphorylation. Immunofluorescence studies using a specific antibody have shown that Aik is localized to the spindle pole during mitosis, especially from prophase through anaphase. These results strongly suggest that Aik is a novel member of a protein kinase family possibly involved in a centrosome function(s) such as chromosome segregation or spindle formation.

Footnotes

↵* This work was supported in part by a grant-in-aid from the Ministry of Education, Science, Sports, and Culture of Japan, and grants from the Life Science Research Project of RIKEN and the Science and Technology Agency of Japan.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

The nucleotide sequence(s) reported in this paper has been submitted to the GenBank™/EMBL Data Bank with accession number(s) D84212.
↵§ To whom correspondence should be addressed. Tel.: 81-58-267-2367; Fax: 81-58-267-2950; E-mail: bunbyo{at}cc.gifu-u.ac.jp.
↵1 The abbreviations used are: PBS, phosphate-buffered saline; kb, kilobase pair(s); TBST, Tris-buffered saline plus Tween 20; DAPI, 4′,6-diamidino-2-phenylindole olihydrochloride.
↵2 An unpublished sequence of mouse Ayk1 (GenBank™ accession no. U80932) has recently been deposited that has high homology with the kinase.
↵3 A gene symbol of STK6 for Aik was obtained from the HUGO Nomenclature Committee of GDB.
- Received February 20, 1997.
- Revision received March 17, 1997.