Thesis

MAP kinase phosphatase-2 in vascular smooth cell muscle function

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Awarding institution
  • University of Strathclyde
Date of award
  • 2013
Thesis identifier
  • T13743
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Abstract
  • The progression of major cardiovascular disorders are a consequence of a pathophysiological modification within the blood vessel; a process often driven by vascular smooth muscle cell hyperproliferation. A major mechanism by which smooth muscle cell proliferation occurs involves ligand-induced activation of MAP kinase signalling (Schad et al., 2011). MAP kinases have been noteworthy but troublesome targets in cardiovascular therapeutics; thus exploration of targeting endogenous regulatory dual specificity proteins namely MAP kinase phosphatases has been advancing in recent years. Mitogen-activated protein kinase phosphatase-2 (MKP-2) is a type 1 nuclear phosphatase with the ability to dephosphorylate and ultimately inactivate MAP kinases ERK and JNK in vitro (Lawan et al., 2012). Therefore, by the use of a novel MKP-2-/- mouse, we assess a role for MKP-2 in smooth muscle proliferation as a potential future therapeutic target in cardiovascular disease. Contrary to current literature, mouse aortic smooth muscle cells cultured from a novel Dusp4 knockout mouse exhibit no significant difference in MAP kinase signalling profiles when compared with wild-type. Interestingly however, a significant reduction in proliferation rate corresponded with MKP-2 knockout cells and further cell cycle investigation elucidated a significant accumulation of MKP-2-/- cells in G2/M phase of the cell cycle. With levels of p-cdc-2 comparable between MKP-2 wild-type and knockout cells, mitotic entry was unaffected by MKP-2 deficiency which therefore diverted our study downstream to cytokinesis. Utilising time-lapse microscopy, smooth muscle cells lacking in MKP-2 exhibited a delay in cytokinesis and failure in abscission, resulting in the dividing cells connected by an intercellular bridge. The molecular mechanism of cytokinesis requires phosphorylation of the mitotic kinase aurora B for successful division of two daughter cells. However nocodazole-arrest studies reveal MKP-2 is required for aurora B phosphorylation and its downstream target histone H3, thus identifying MKP-2 as essential in the effective completion of cytokinesis. Within this thesis, an early investigation into the possible use of Adv.WT-MKP-2 as a vascular therapeutic in human aortic smooth muscle cells (HASMCs) was conducted. The over-expression of MKP-2 negated ERK signalling and consequently resulted in a reduction in cellular proliferation. Furthermore, the reduction in cellular proliferation was shown to be caused by a G1/S accumulation in the cell cycle. Collectively, these data suggest a novel role for MKP-2 in mouse aortic smooth muscle cell proliferation, providing new insights into the understanding of MKP-2 in the completion of cytokinesis. Furthermore, MKP-2 kinase binding domain is required for successful completion of cytokinesis but may not involve the inactivation of ERK or JNK. Therefore, modification of MKP-2 expression or function may represent a new approach in reducing SMC hyperproliferation in vascular disease states.
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DOI
Date Created
  • 2013
Former identifier
  • 1032633

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