Aurora A Kinase Amplifies a Midzone Phosphorylation Gradient to Promote High-Fidelity Cytokinesis

Aurora kinases: Generators of spatial control during mitosis

Cell division events require regulatory systems to ensure that events happen in a distinct order. The classic view of temporal control of the cell cycle posits that cells order events by linking them to changes in Cyclin Dependent Kinase (CDK) activities. However, a new paradigm is emerging from studies of anaphase where chromatids separate at the central metaphase plate and then move to opposite poles of the cell. These studies suggest that distinct events are ordered depending upon the location of each chromosome along its journey from the central metaphase plate to the elongated spindle poles. This system is dependent upon a gradient of Aurora B kinase activity that emerges during anaphase and acts as a spatial beacon to control numerous anaphase/telophase events and cytokinesis. Recent studies also suggest that Aurora A kinase activity specifies proximity of chromosomes or proteins to spindle poles during prometaphase. Together these studies argue that a key role for Aurora kinases is to provide spatial information that controls events depending upon the location of chromosomes or proteins along the mitotic spindle.

Insights into the non-mitotic functions of Aurora kinase A: more than just cell division

AURKA is a serine/threonine kinase overexpressed in several cancers. Originally identified as a protein with multifaceted roles during mitosis, improvements in quantitative microscopy uncovered several non-mitotic roles as well. In physiological conditions, AURKA regulates cilia disassembly, neurite extension, cell motility, DNA replication and senescence programs. In cancer-like contexts, AURKA actively promotes DNA repair, it acts as a transcription factor, promotes cell migration and invasion, and it localises at mitochondria to regulate mitochondrial dynamics and ATP production. Here we review the non-mitotic roles of AURKA, and its partners outside of cell division. In addition, we give an insight into how structural data and quantitative fluorescence microscopy allowed to understand AURKA activation and its interaction with new substrates, highlighting future developments in fluorescence microscopy needed to better understand AURKA functions in vivo. Last, we will recapitulate the most significant AURKA inhibitors currently in clinical trials, and we will explore how the non-mitotic roles of the kinase may provide new insights to ameliorate current pharmacological strategies against AURKA overexpression.

Classical and Emerging Regulatory Mechanisms of Cytokinesis in Animal Cells

The primary goal of cytokinesis is to produce two daughter cells, each having a full set of chromosomes. To achieve this, cells assemble a dynamic structure between segregated sister chromatids called the contractile ring, which is made up of filamentous actin, myosin-II, and other regulatory proteins. Constriction of the actomyosin ring generates a cleavage furrow that divides the cytoplasm to produce two daughter cells. Decades of research have identified key regulators and underlying molecular mechanisms; however, many fundamental questions remain unanswered and are still being actively investigated. This review summarizes the key findings, computational modeling, and recent advances in understanding of the molecular mechanisms that control the formation of the cleavage furrow and cytokinesis.

Microtubule plus-ends act as physical signaling hubs to activate RhoA during cytokinesis

Microtubules (MTs) are essential for cleavage furrow positioning during cytokinesis, but the mechanisms by which MT-derived signals spatially define regions of cortical contractility are unresolved. In this study cytokinesis regulators visualized in Drosophila melanogaster (Dm) cells were found to localize to and track MT plus-ends during cytokinesis. The RhoA GEF Pebble (Dm ECT2) did not evidently tip-track, but rather localized rapidly to cortical sites contacted by MT plus-tips, resulting in RhoA activation and enrichment of myosin-regulatory light chain. The MT plus-end localization of centralspindlin was compromised following EB1 depletion, which resulted in a higher incidence of cytokinesis failure. Centralspindlin plus-tip localization depended on the C-terminus and a putative EB1-interaction motif (hxxPTxh) in RacGAP50C. We propose that MT plus-end-associated centralspindlin recruits a cortical pool of Dm ECT2 upon physical contact to activate RhoA and to trigger localized contractility.

Regulation and Assembly of Actomyosin Contractile Rings in Cytokinesis and Cell Repair

Cytokinesis and single-cell wound repair both involve contractile assemblies of filamentous actin (F-actin) and myosin II organized into characteristic ring-like arrays. The assembly of these actomyosin contractile rings (CRs) is specified spatially and temporally by small Rho GTPases, which trigger local actin polymerization and myosin II contractility via a variety of downstream effectors. We now have a much clearer view of the Rho GTPase signaling cascade that leads to the formation of CRs, but some factors involved in CR positioning, assembly, and function remain poorly understood. Recent studies show that this regulation is multifactorial and goes beyond the long-established Ca²⁺ -dependent processes. There is substantial evidence that the Ca²⁺ -independent changes in cell shape, tension, and plasma membrane composition that characterize cytokinesis and single-cell wound repair also regulate CR formation. Elucidating the regulation and mechanistic properties of CRs is important to our understanding of basic cell biology and holds potential for therapeutic applications in human disease. In this review, we present a primer on the factors influencing and regulating CR positioning, assembly, and contraction as they occur in a variety of cytokinetic and single-cell wound repair models. Anat Rec, 301:2051-2066, 2018. © 2018 Wiley Periodicals, Inc.