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IDENTIFCATION OF THE CAUSES OF CYTOKINESIS FAILURE IN CANCER CELLS

Sahasrabudhe, Ruta (2012) IDENTIFCATION OF THE CAUSES OF CYTOKINESIS FAILURE IN CANCER CELLS. Doctoral Dissertation, University of Pittsburgh.

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    Abstract

    Tetraploidy and chromosomal instability are common phenotypes of malignant cells and cytokinesis failure is a known source of tetraploidy. However, the causes of cytokinesis failure are not yet identified. An essential step in the process of cytokinesis is phosphorylation of myosin regulatory light chain (MLC), required for actin–myosin interaction and the formation of the cleavage furrow. Our data indicate that cancer cells are deficient in MLC phosphorylation and this deficiency is the cause of cytokinesis failure. Myosin light chain kinase (MLCK) is a key enzyme that phosphorylates MLC during cytokinesis and is inhibited in cancer cells. Aurora B kinase is an essential regulator of cytokinesis that is commonly over-expressed in cancer cells and can phosphorylate MLCK in vitro. Therefore we hypothesize that Aurora B over-expression is the cause of MLCK inhibition in cancer cells. Consistent with our hypothesis, we demonstrate that Aurora B kinase indeed is an MLCK inhibitor in vitro and in cultured mammalian cells. Cytokinesis failure resulting from Aurora B over-expression can largely be suppressed by constitutively active MLCK or phosphomimetic MLC and reducing protein levels of Aurora B in cancer cells increases MLCK activity and decreases cytokinesis failure. These data thus describe a novel pathway that drives Aurora B induced cytokinesis failure. Cytokinesis failure is often observed in only a subset of cancer cells but the trigger for this divisional failure in that subset is unknown. One strong possibility is the presence of lingering chromatin at the cleavage site that has been previously proposed to block cytokinesis completion. However, the mechanism linking lingering chromatin and cytokinesis failure is still a mystery. In this study we demonstrate that lingering chromatin causes cytokinesis failure by inducing over-expression of Aurora B and the resultant inhibition of MLCK and phosphorylated MLC. Together, my results define a novel pathway for Aurora B mediated regulation of cytokinesis and contribute to our understanding of the genomic destabilizing events of tumorigenesis.


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    Item Type: University of Pittsburgh ETD
    Creators/Authors:
    CreatorsEmailORCID
    Sahasrabudhe, Rutarms62@pitt.edu
    ETD Committee:
    ETD Committee TypeCommittee MemberEmailORCID
    Committee ChairSaunders, Williamwsaund@pitt.edu
    Committee MemberBrodsky, Jeffreyjbrodsky@pitt.edu
    Committee MemberKiselyov, Kirillkiselyov@pitt.edu
    Committee MemberProchownik, Edwardprochownikev@upmc.edu
    Committee MemberSchwacha, Anthonyschwacha@pitt.edu
    Title: IDENTIFCATION OF THE CAUSES OF CYTOKINESIS FAILURE IN CANCER CELLS
    Status: Published
    Abstract: Tetraploidy and chromosomal instability are common phenotypes of malignant cells and cytokinesis failure is a known source of tetraploidy. However, the causes of cytokinesis failure are not yet identified. An essential step in the process of cytokinesis is phosphorylation of myosin regulatory light chain (MLC), required for actin–myosin interaction and the formation of the cleavage furrow. Our data indicate that cancer cells are deficient in MLC phosphorylation and this deficiency is the cause of cytokinesis failure. Myosin light chain kinase (MLCK) is a key enzyme that phosphorylates MLC during cytokinesis and is inhibited in cancer cells. Aurora B kinase is an essential regulator of cytokinesis that is commonly over-expressed in cancer cells and can phosphorylate MLCK in vitro. Therefore we hypothesize that Aurora B over-expression is the cause of MLCK inhibition in cancer cells. Consistent with our hypothesis, we demonstrate that Aurora B kinase indeed is an MLCK inhibitor in vitro and in cultured mammalian cells. Cytokinesis failure resulting from Aurora B over-expression can largely be suppressed by constitutively active MLCK or phosphomimetic MLC and reducing protein levels of Aurora B in cancer cells increases MLCK activity and decreases cytokinesis failure. These data thus describe a novel pathway that drives Aurora B induced cytokinesis failure. Cytokinesis failure is often observed in only a subset of cancer cells but the trigger for this divisional failure in that subset is unknown. One strong possibility is the presence of lingering chromatin at the cleavage site that has been previously proposed to block cytokinesis completion. However, the mechanism linking lingering chromatin and cytokinesis failure is still a mystery. In this study we demonstrate that lingering chromatin causes cytokinesis failure by inducing over-expression of Aurora B and the resultant inhibition of MLCK and phosphorylated MLC. Together, my results define a novel pathway for Aurora B mediated regulation of cytokinesis and contribute to our understanding of the genomic destabilizing events of tumorigenesis.
    Date: 02 October 2012
    Date Type: Publication
    Defense Date: 24 May 2012
    Approval Date: 02 October 2012
    Submission Date: 05 June 2012
    Release Date: 02 October 2012
    Access Restriction: 5 year -- Restrict access to University of Pittsburgh for a period of 5 years.
    Patent pending: No
    Number of Pages: 178
    Institution: University of Pittsburgh
    Thesis Type: Doctoral Dissertation
    Refereed: Yes
    Degree: PhD - Doctor of Philosophy
    Uncontrolled Keywords: cancer, cytokinesis, MLCK, Aurora B kinase
    Schools and Programs: Dietrich School of Arts and Sciences > Biological Sciences
    Date Deposited: 02 Oct 2012 15:03
    Last Modified: 16 Jul 2014 17:06

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