| The Aurora kinases family, belonging to serine/threonine protein kinases, is currently one of the most intensely studied families that regulate many processes during cell division. In mammalian cells, it comprises Aurora A, B and C.Aurora A is localized at the spindle poles from prophase to telophase and has emerged as a critical factor in the assembly of the mitotic spindle. Depletion of Aurora A by RNAi (RNA interference) disrupts centrosomal recruitment of D-TACC (Drosophila transforming-acidic-coiled-coil protein), centrosomin in D. melanogaster and γ-tubulin in S. cerevisiae, leading to defects in microtubule and centrosome morphology. Over-expression of Aurora A causes an increase in centrosome number and aneuploidy, leading to the transformation of mammalian cells.Aurora B is a chromosomal passenger protein. It can phosphorylate Histone H3 in mammals. In D. melanogaster, H3 fails to be phosphorylated during mitosis after Aurora B was deleted by RNAi, and both chromosome condensation and segregtion are defective. In C. elegance, disruption of Aurora B by RNAi leads to polyploidy. Many lines of evidences show that Aurora B is associated with other two passenger proteins, Survivin and INCENP (inner centromere protein). Disruption of any one of these three proteins interferes with the localizations of the other two, indicating that their accurate targetings and functions during mitosis require each other. Intriguingly, each of Aurora B, Survivin and INCENP is detected to be over-expressed in many cancer cell lines. These facts lead to the idea that the coordinated increases in the complex and the enhanced Aurora B activity through increased expression of Survivin, are important to transformation or tumor formation.Although a large amount of research has been carried out on the highly conserved members of Aurora kinases family such as Ipllp (increase-in-ploidy 1) (Schizosaccharomyces cerevisiae), AIRs (Aurora/Ipllp related kinases) (Caenorhabditis elegans), Aurora and IAL (Drosophila melanogaster), pEGl and pEG2 (Xenopus laevis), human Aurora A and B, less is known about this third human Aurora kinase, Aurora C.Aurora C, highly expressed in mammalian testis, was first identified in a screen for kinases expressed in mouse sperm and eggs. Its gene maps to 19q13.43, a region often translocated or deleted in certain cancer tissues, and its protein product is also over-expressed in certain cancer cell lines and in primary colorectal cancers. AuroraC protein level is low during S phase and peaks at mitosis. In earlier study Aurora C appears at centrosomes in anaphase and remains there till cytokinesis. However, except for the results mentioned above, the real biological functions of Aurora C in mitosis remain problems. The details of the subcellular distribution of Aurora C and its distinct functions in normal and cancer cells have become the fascinating questions to be clarified.When Aurora C was amplified from human testis cDNA library, we accidentally obtained another new splicing variant except for the Aurora C cDNA that had been reported. This distinct splicing variant encodes an N-terminal shortened protein. We named this novel splicing variant Aurora C-SV (Splicing Variant). Through RT-PCR in 18 tissues, we found that Aurora C-SV, like Aurora C, is expressed the most in testis. Further more, using sensitive RT-PCR to amplify the C-terminal, we found that Aurora C is not only expressed highly in testis, but also among other 16 human tissues in a broad-spectrum way. The expression level of Aurora C does not change obviously in liver tumor and normal liver tissues. The in vitro kinase assay showed that both Aurora C and Aurora C-SV were able to phosphorylate MBP as Aurora A and B. Their D166Y and T179A mutant, respectively, lost the kinase activity.In order to characterize the subcellular localization of Aurora C, we transiently transfected HeLa cells with this kinase fused with EGFP. Aurora C was also shown, during mitosis, to have a chromosomal localization during prophase and metaphase, to move to the spindle midzone when the sister chromatids start to separate, to subsequently relocate to the cortex of the contractile ring during telophase, and to remain in the midbody during cytokinesis. So we thought Aurora C is a novel chromosomal passenger protein. Next, we also found that Aurora C is co-localized with Aurora B and Survivin in mitotic cells. Meanwhile, Aurora C can form into a complex with Aurora B and Survivin, and be directly associated with Survivin but not Aurora B.Like Aurora B, the kinase activity of Aurora C contributes to its proper localization. Both the catalytically inactive Aurora C and its WT (wild type) are demonstrated to lead to the multinucleation in cells, which gave us an indication that Aurora C is required for cytokinesis. Aurora C WT is able to rescue the multinucleation induced by catalytically inactive Aurora B, vice versa. And Aurora C WT is also able to rescue the multinucleation induced by Aurora B-targeting RNAi. Taken together, these results lead to the hypothesis that Aurora C might possess the similar function...
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