Interaction between ROCK II and Nucleophosmin/B23 in the Regulation of Centrosome Duplication

Department of Cell Biology, University of Cincinnati College of Medicine, 3125 Eden Avenue, Cincinnati, OH 45267-0521, USA.
Molecular and Cellular Biology (Impact Factor: 4.78). 01/2007; 26(23):9016-34. DOI: 10.1128/MCB.01383-06
Source: PubMed


Nucleophosmin (NPM)/B23 has been implicated in the regulation of centrosome duplication. NPM/B23 localizes between two centrioles
in the unduplicated centrosome. Upon phosphorylation on Thr199 by cyclin-dependent kinase 2 (CDK2)/cyclin E, the majority of centrosomal NPM/B23 dissociates from centrosomes, but some
NPM/B23 phosphorylated on Thr199 remains at centrosomes. It has been shown that Thr199 phosphorylation of NPM/B23 is critical for the physical separation of the paired centrioles, an initial event of the centrosome
duplication process. Here, we identified ROCK II kinase, an effector of Rho small GTPase, as a protein that localizes to centrosomes
and physically interacts with NPM/B23. Expression of the constitutively active form of ROCK II promotes centrosome duplication,
while down-regulation of ROCK II expression results in the suppression of centrosome duplication, especially delaying the
initiation of centrosome duplication during the cell cycle. Moreover, ROCK II regulates centrosome duplication in its kinase
and centrosome localization activity-dependent manner. We further found that ROCK II kinase activity is significantly enhanced
by binding to NPM/B23 and that NPM/B23 acquires a higher binding affinity to ROCK II upon phosphorylation on Thr199. Moreover, physical interaction between ROCK II and NPM/B23 in vivo occurs in association with CDK2/cyclin E activation and
the emergence of Thr199-phosphorylated NPM/B23. All these findings point to ROCK II as the effector of the CDK2/cyclin E-NPM/B23 pathway in the regulation
of centrosome duplication.

Download full-text


Available from: Kozo Kaibuchi, Jul 02, 2014
22 Reads
  • Source
    • "Loss of RASSF1A or RAB6C [47],[48] or over-activation of Ras and Rho small GTPases [8],[49] induces centrosome amplification, multipolar spindles and aneuploidy. While mechanisms by which RAB6C prevents centrosome amplification are undefined, several of the other GTPases have been shown to act through pathways involving phosphorylated NPM-T199 [8],[50], similar to RABL6A. For instance, Ras promotes Cdk2 and Cdk4-mediated phosphorylation of NPM-T199 [8] whereas Rho A binds and partially activates the Rho associated kinase, ROCK II, priming it for super-activation by association with phosphorylated NPM-T199 [50]. "
    [Show abstract] [Hide abstract]
    ABSTRACT: RABL6A (RAB-like 6 isoform A) is a novel protein that was originally identified based on its association with the Alternative Reading Frame (ARF) tumor suppressor. ARF acts through multiple p53-dependent and p53-independent pathways to prevent cancer. How RABL6A functions, to what extent it depends on ARF and p53 activity, and its importance in normal cell biology are entirely unknown. We examined the biological consequences of RABL6A silencing in primary mouse embryo fibroblasts (MEFs) that express or lack ARF, p53 or both proteins. We found that RABL6A depletion caused centrosome amplification, aneuploidy and multinucleation in MEFs regardless of ARF and p53 status. The centrosome amplification in RABL6A depleted p53-/- MEFs resulted from centrosome reduplication via Cdk2-mediated hyperphosphorylation of nucleophosmin (NPM) at threonine-199. Thus, RABL6A prevents centrosome amplification through an ARF/p53-independent mechanism that restricts NPM-T199 phosphorylation. These findings demonstrate an essential role for RABL6A in centrosome regulation and maintenance of chromosome stability in non-transformed cells, key processes that ensure genomic integrity and prevent tumorigenesis.
    PLoS ONE 11/2013; 8(11):e80228. DOI:10.1371/journal.pone.0080228 · 3.23 Impact Factor
  • Source
    • "Reduced mRNA levels of RhoE further correlate with disease progression in breast and prostate cancer, possibly due to increased ROCK I activity (Pinner and Sahai 2008; Belgiovine et al. 2010). Similarly, morgana/chp-1 and nucleophosmin/B23 (NPM/ B23) compete for binding on ROCK II, thereby regulating ROCK II activity, centrosome duplication, and neoplastic transformation (Ma Z et al. 2006; Ferretti et al. 2010). Downregulation of endogenous ROCK inhibitors in cancer could potentiate more aggressive migratory and invasive behavior. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Cancer-associated changes in cellular behavior, such as modified cell-cell contact, increased migratory potential, and generation of cellular force, all require alteration of the cytoskeleton. Two homologous mammalian serine/threonine kinases, Rho-associated protein kinases (ROCK I and II), are key regulators of the actin cytoskeleton acting downstream of the small GTPase Rho. ROCK is associated with cancer progression, and ROCK protein expression is elevated in several types of cancer. ROCKs exist in a closed, inactive conformation under quiescent conditions, which is changed to an open, active conformation by the direct binding of guanosine triphosphate (GTP)–loaded Rho. In recent years, a number of ROCK isoform-specific binding partners have been found to modulate the kinase activity through direct interactions with the catalytic domain or via altered cellular localization of the kinases. Thus, these findings demonstrate additional modes to regulate ROCK activity. This review describes the molecular mechanisms of ROCK activity regulation in cancer, with emphasis on ROCK isoform-specific regulation and interaction partners, and discusses the potential of ROCKs as therapeutic targets in cancer.
    Journal of Histochemistry and Cytochemistry 11/2012; 61(3). DOI:10.1369/0022155412470834 · 1.96 Impact Factor
  • Source
    • "NPM was reported to have the ability to control centrosome duplication in association with ROCK2 (Ma et al., 2006b), a member of the Rho-associated, coiled-coil containing protein kinase family that is frequently overexpressed in cancer (Nishimura et al., 2003). After NPM phosphorylation by CDK2–cyclin E, the binding between NPM and ROCK2 increases and ROCK2 is activated at centrosomes, leading to centrosome duplication (Ma et al., 2006b). In ROCK2 activation, the binding of Rho small GTPase to the auto-inhibitory region is also required (Kanai et al., 2010). "
    Lung Diseases - Selected State of the Art Reviews, 03/2012; , ISBN: 978-953-51-0180-2
Show more