Change search
ReferencesLink to record
Permanent link

Direct link
Aneugenic activity of Op18/stathmin is potentiated by the somatic Q18-->e mutation in leukemic cells.
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)
Umeå University, Faculty of Medicine, Molecular Biology (Faculty of Medicine). (Gullberg)
2006 (English)In: Mol Biol Cell, ISSN 1059-1524, Vol. 17, no 7, 2921-2930 p.Article in journal (Refereed) Published
Abstract [en]

Op18/stathmin (Op18) is a phosphorylation-regulated microtubule destabilizer that is frequently overexpressed in tumors. The importance of Op18 in malignancy was recently suggested by identification of a somatic Q18-->E mutation of Op18 in an adenocarcinoma. We addressed the functional consequences of aberrant Op18 expression in leukemias by analyzing the cell cycle of K562 cells either depleted of Op18 by expression of interfering hairpin RNA or induced to express wild-type or Q18E substituted Op18. We show here that although Op18 depletion increases microtubule density during interphase, the density of mitotic spindles is essentially unaltered and cells divide normally. This is consistent with phosphorylation-inactivation of Op18 during mitosis. Overexpression of wild-type Op18 results in aneugenic activities, manifest as aberrant mitosis, polyploidization, and chromosome loss. One particularly significant finding was that the aneugenic activity of Op18 was dramatically increased by the Q18-->E mutation. The hyperactivity of mutant Op18 is apparent in its unphosphorylated state, and this mutation also suppresses phosphorylation-inactivation of the microtubule-destabilizing activity of Op18 without any apparent effect on its phosphorylation status. Thus, although Op18 is dispensable for mitosis, the hyperactive Q18-->E mutant, or overexpressed wild-type Op18, exerts aneugenic effects that are likely to contribute to chromosomal instability in tumors.

Place, publisher, year, edition, pages
2006. Vol. 17, no 7, 2921-2930 p.
Keyword [en]
Aneugens/metabolism, Cell Cycle/genetics, Chromosomal Instability, Humans, Leukemia/*genetics/metabolism/pathology, Microtubules/metabolism, Mitosis/genetics, Mitotic Spindle Apparatus/*metabolism, Mutation, Phosphorylation, RNA Interference, Stathmin/antagonists & inhibitors/*genetics/*metabolism, Tubulin/metabolism
URN: urn:nbn:se:umu:diva-16501DOI: 10.1091/mbc.E06-02-0165PubMedID: 16624860OAI: diva2:156174
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

Open Access in DiVA

No full text

Other links

Publisher's full textPubMed

Search in DiVA

By author/editor
Holmfeldt, PerBrännström, KristofferStenmark, SonjaGullberg, Martin
By organisation
Molecular Biology (Faculty of Medicine)

Search outside of DiVA

GoogleGoogle Scholar
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

Altmetric score

Total: 73 hits
ReferencesLink to record
Permanent link

Direct link