Mechanism of Aurora-B Degradation and Its Dependency on Intact KEN and A-Boxes: Identification of an Aneuploidy-Promoting Property

Abstract

The kinase Aurora-B, a regulator of chromosome segregation and cytokinesis, is highly expressed in a variety of tumors. During the cell cycle, the level of this protein is tightly controlled, and its deregulated abundance is suspected to contribute to aneuploidy. Here, we provide evidence that Aurora-B is a short-lived protein degraded by the proteasome via the anaphase-promoting cyclosome complex (APC/c) pathway. Aurora-B interacts with the APC/c through the Cdc27 subunit, Aurora-B is ubiquitinated, and its level is increased upon treatment with inhibitors of the proteasome. Aurora-B binds in vivo to the degradation-targeting proteins Cdh1 and Cdc20, the overexpression of which accelerates Aurora-B degradation. Using deletions or point mutations of the five putative degradation signals in Aurora-B, we show that degradation of this protein does not depend on its D-boxes (RXXL), but it does require intact KEN boxes and A-boxes (QRVL) located within the first 65 amino acids. Cells transfected with wild-type or A-box-mutated or KEN box-mutated Aurora-B fused to green fluorescent protein display the protein localized to the chromosomes and then to the midzone during mitosis, but the mutated forms are detected at greater intensities. Hence, we identified the degradation pathway for Aurora-B as well as critical regions for its clearance. Intriguingly, overexpression of a stable form of Aurora-B alone induces aneuploidy and anchorage-independent growth.

FBXW7 is involved in Aurora B degradation

“…So far, there is evidence for the involvement of two ubiquitin E3 ligases involved in ubiquitin-mediated degradation of Aurora B: anaphase-promoting cyclosome complex (APC/c) 29,30 and a Cullin 3 (Cul3)-based E3 ligase with the substrate-specific adaptors KLHL9 and KLHL13. 31 Aurora B interacts with APC/c through the Cdc27 subunit.…”

Expression of the kinetochore protein Hec1 during the cell cycle in normal and cancer cells and its regulation by the pRb pathway

“…An increased recruitment of Hec1 at kinetochores was also observed in cancer cells. Most eukaryotic kinetochores are large protein assemblies containing multiple (15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30) attachment sites for the plus-end of spindle MT. 6,7 Between six and eight Ndc80 complexes are thought to encircle each attachment site and function as a dynamic grasp for MT.…”

Cell cycle regulation of the human Six1 homeoprotein is mediated by APCCdh1

“…Another degradation motif, the A-box (Q-R-V-L), is present in the Aurora kinases Aur-A and Aur-B, which also contain a functional KEN box (Crane et al, 2004;Nguyen et al, 2005). In Aur-A, a serine residue just downstream of the A-box is phosphorylated specifically in mitosis.…”