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Differential functional interplay of TOGp/XMAP215 and the KinI kinesin MCAK during interphase and mitosis.
Umeå University, Faculty of Medicine, Molecular Biology (Faculty of Medicine). (Gullberg)
Umeå University, Faculty of Medicine, Molecular Biology (Faculty of Medicine). (Gullberg)
Umeå University, Faculty of Medicine, Molecular Biology (Faculty of Medicine). (Gullberg)
2004 (English)In: EMBO J, ISSN 0261-4189, Vol. 23, no 3, 627-637 p.Article in journal (Refereed) Published
Abstract [en]

XMAP215/TOGp family members and KinI kinesins are conserved microtubule (MT)-regulatory proteins, and have been viewed as possessing prominent antagonistic stabilizing/destabilizing activities that must be balanced. Here, interdependencies between TOGp and the KinI kinesin MCAK were analyzed in human leukemia cells. A system was established that permits inducible overexpression in homogeneous cell populations that simultaneously synthesize interfering short hairpin RNAs. We present evidence that the functional interplay of TOGp and MCAK proteins is manifested as three distinct phenotypes during the cell cycle. The first involves a role for TOGp in protecting spindle MTs from MCAK activity at the centrosome, which appears essential to prevent the formation of disorganized multipolar spindles. The second phenotype involves TOGp-dependent counteraction of excessive MCAK activity during mitosis, which recapitulates the previously established plus-end specific counteractive activities in vitro. The third involves an unexpected destabilization of the interphase MTs by overexpressed TOGp, a phenotype that requires endogenous MCAK. We hypothesize that TOGp-dependent prevention of MCAK-mediated spindle disorganization, as evidenced by depletion experiments, reflects a primary physiological role for TOGp in human somatic cells.

Place, publisher, year, edition, pages
2004. Vol. 23, no 3, 627-637 p.
Keyword [en]
Humans, Interphase/*physiology, K562 Cells, Kinesin/*metabolism, Microtubule-Associated Proteins/*metabolism, Mitosis/*physiology, Mitotic Spindle Apparatus/*metabolism
URN: urn:nbn:se:umu:diva-16504DOI: 10.1038/sj.emboj.7600076PubMedID: 14749730OAI: diva2:156177
Available from: 2007-10-04 Created: 2007-10-04Bibliographically approved
In thesis
1. Regulation of tubulin heterodimer partitioning during interphase and mitosis
Open this publication in new window or tab >>Regulation of tubulin heterodimer partitioning during interphase and mitosis
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The microtubule cytoskeleton, which consists of dynamic polymers of alpha/beta tubulin heterodimers, organizes the cytoplasm and is essential for chromosome segregation during mitosis. My thesis addresses the significance and potential interplay between four distinct microtubule-regulatory proteins. The experimental approach included the development of a replicating vector system directing either constitutive expression of short hairpin RNAs or inducible ectopic expression, which allows stable depletion and/or conditional exchange of gene-products.

Based on the originally observed activities in frog egg extracts, MCAK and TOGp have been viewed as major antagonistic proteins that regulate microtubule-dynamics throughout the cell cycle. Surprisingly, while my thesis work confirmed an essential role of these proteins to ensure mitotic fidelity, tubulin subunits partitioning is not controlled by the endogenous levels of MCAK and TOGp in human somatic cells. Our major discovery in these studies is that the activities of both CaMKII and TOGp are essential for spindle bipolarity through a mechanism involving protection of spindle microtubules against MCAK activity at the centrosome.

In our search for the major antagonistic activities that regulates microtubule-dynamics in interphase cells, we found that the microtubule-destabilizing activity of Op18 is counteracted by MAP4. These studies also established Op18 and MAP4 as the predominant regulators of tubulin subunit partitioning in all three human cell model systems studied. Moreover, consistent with phosphorylation-inactivation of these two proteins during mitosis, we found that the microtubule-regulatory activities of both MAP4 and Op18 were only evident in interphase cells. Importantly, by employing a system for inducible gene product replacement, we found that site-specific phosphorylation-inactivation of Op18 is the direct cause of the demonstrated hyper-polymerization in response to T-cell antigen receptor triggering. This provides the first formally proven example of a signal transduction pathway for regulation of interphase microtubules.

Op18 is frequently upregulated in various types of human malignancies. In addition, a somatic mutation of Op18 has recently been identified in an adenocarcinoma. This thesis work revealed that the mutant Op18 protein exerts increased microtubule-destabilizing activity. The mutant Op18 protein was also shown to be partially resistant to phosphorylation-inactivation during mitosis, which was associated with increased chromosome segregation aberrancies. Interestingly, we also observed the same phenotype by overexpressing the wild type Op18 protein. Thus, either excessive levels of wild type Op18 or normal levels of mutated hyper-active Op18 seems likely to contribute to tumor progression by exacerbating chromosomal instability.

Place, publisher, year, edition, pages
Umeå: Molekylärbiologi (Medicinska fakulteten), 2008. 30 p.
Umeå University medical dissertations, ISSN 0346-6612 ; 1220
microtubule, mitotic spindle, signal transduction, phosphorylation, cancer
National Category
Biochemistry and Molecular Biology
urn:nbn:se:umu:diva-1923 (URN)978-91-7264-670-4 (ISBN)
Public defence
2008-12-16, Major groove, 6L, Umeå, 10:00 (English)
Available from: 2008-11-18 Created: 2008-11-18 Last updated: 2010-01-18Bibliographically approved

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Holmfeldt, PerStenmark, SonjaGullberg, Martin
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