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Hanna-Stina Martinsson Ahlzén
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| Project Overview |
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| Background |
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Cancer, which is the second leading cause of death in the industrial world, is caused by genetic alterations that result in uncontrolled cell growth. Among the most frequently upregulated genes in many cancer types are CKS1 and CKS2, which encode cyclin dependent kinase-associated proteins Cks1 and Cks2. Upregulation of CKS gene expression has been found in breast, colon, gastric, ovary, and lung carcinomas as well as in leukemias and lymphomas. Moreover, CKS transcriptional upregulation has been shown to correlate with poor prognosis in breast cancer. Despite the strong correlation it is not clear if and how upregulation CKS contributes to cancer. |
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Cks proteins are evolutionarily conserved from yeast to man and interact with cyclin dependent kinases (Cdks). Loss of Cks function has been shown to arrest cells in M-phase in yeast and in Xenopus egg extracts. On a molecular level, Cks has been shown to enhance the phosphorylation of various mitotic Cdk substrates in Xenopus and to promote the degradation of the B-type cyclin Clb2 and the anaphase inhibitor Pds1 in budding yeast. More importantly it has been shown that an important function of Cks in budding yeast is to act as an essential co-activator of CDC20 transcription, which encodes a. Cdc20 is a substrate recognition factor and activator of the APC/Cyclosome complex, which polyubiquitinylates specific mitotic regulators, thereby targeting them for destruction and promoting passage through M-phase. It has also been shown that theCks1/Cdc28 complex has a role in transcriptional control. This role of Cks1/Cdc28 is independent of both the Cdc28 kinase function and cell cycle position and appears to involve chromatin remodelling. |
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In contrast to yeast, humans and mice encode two Cks orthologs, Cks1 and Cks2. Mice nullizygous for either gene are viable, whereas deletion of both copies leads to embryonic lethality. CKS1 inactivation leads to abnormally small mice that are deficient in the degradation of the G1/S Cdk inhibitor p27Kip1. Mice lacking CKS2 are normal except for being sterile in both sexes. Sterility is due to failure of germ cells to progress past the first meiotic metaphase. The meiotic arrest results from a lack of CKS1 expression in germ cells. This result together with the observation that mice lacking both CKS genes die at an early stage of embryogenesis, indicates that Cks1 and Cks2 share a so far unknown essential function in mammalian cells. |
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The specific goals of this project are to investigate the role of Cks proteins in the mammalian cell cycle and to characterize the role of Cks proteins in transcription in mammalian cells. Another objective of this project is to examine how artificially altering the Cks1 and Cks2 expression levels in mammalian cells effects gene transcription. Knowledge about the role of the Cks proteins in mammals and how altering their expression affects genetranscription is critical for elucidating the relationship between deregulation of Cks protein expression and cancer. |
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The role of Cks proteins in the mammalian cell cycle and transcription |
To address these questions we investigated the phenotype of CKS1-/- CKS2-/- nullizygous mice and of mouse and human cell lines depleted of Cks proteins by RNA interference. The nullizygous mice die before implantation in the morula stage which is one of the earliest times for embryonic lethality reported for cell cycle genes. To investigate the function of Cks proteins in somatic mammalian cells Cks proteins were depleted using RNAi. We found that in the absence of Cks proteins the cells stopped proliferating. In HeLa cells the arrested cells underwent apoptosis. In the case of MEFs the cells arrested in the G2 phase of the cell cycle. The arrest was followed by rereplication without cell division leading to polyploidy due to a defect in transcribing the CCNB1, CCNA2 and CDK1 genes. Trying to mimic this phenotype we found that depleting the MEFs of cyclin B gave a similar phenotype as the Cks depleted cells and we also discovered that ectopically expressing cyclin B in Cks depleted cells restores cell proliferation. Using ChIP analysis we found that Cdk1 binds to the promoters and ORFs of CCNB1 and CDK1 genes in cell cycle specific fashion that correlates with their transcription. |
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| Curriculum Vitae |
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Hanna-Stina Martinsson Ahlzén
Research Associate
The Scripps Research Institute
Department of Molecular Biology
10550 North Torrey Pines Road, MB-7
La Jolla CA 92037
Phone: 858-784-2304
Fax: 858-784-2781
Email: hanmar@scripps.edu |
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| Education |
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Undergraduate studies, Biochemistry
Uppsala Universitet, Uppsala, Sweden
January 1995 – June 1999
Ph.D., Pathology, cytology and experimental pathology
Karolinska Institutet, Stockholm, Sweden
October 2005
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| Research and Professional Experience |
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| 2005-present |
Research Associate, Department of Molecular Biology, The Scripps Research Institute, La Jolla, California, Laboratory of Steven I Reed |
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| 2000-2005 |
Graduate Student, Department of Oncology-Pathology, Karolinska Institutet, Stockholm, Sweden, Advisors: Anders Zetterberg and Maria Starborg |
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| July-Dec. 1999 |
Biochemist, Medicarb AB, Bromma, Sweden |
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| Honors |
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| July – Nov. 2005 |
Postgraduate studentship from The Board for Postgraduate Education |
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| Publications |
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Martinsson Ahlzén H-S, Liberal V, Grünenfelder B, Chaves SR, Spruck CH and Reed SI, “Cyclin-dependent kinase proteins Cks1 and Cks2 are essential during early embryogenesis and for cell cycle progression in somatic cells”, Mol Cell Biol., 2008;28:5698-5709
Cosaceanu D, Carapancea M, Alexandru O, Budiu R, Martinsson H-S, Starborg M, Vrabete M, Kanter L, Lewensohn R and Dricu A, “Comparison of three approaches for inhibiting insuline-like growth factor I receptor and their effects on NSCLC cell lines in vitro”, Growth Factors 2007;25(1):1-8
Erlandsson F, Martinsson-Ahlzén H-S, Walling KL, Hellström AC, Andersson S and Zetterberg A, ”Parallell cyclin E and cyclin A expression in neoplastic lesions of the uterine cervix”, Br. J. Cancer 2006;94(7):1045-50
Martinsson H-S, Starborg M, Erlandsson F and Zetterberg A, “Single cell analysis of G1 checkpoints – The relationship between the restriction point and phosphorylation of pRb”, Exp. Cell Res 2005;305(2);383-91
Martinsson H-S, Zickert P, Starborg M, Larsson O and Zetterberg A, “Changes in cell shape and anchorage in relation to the restriction point”, J. Cell Physiol. 2005;203(1);23-34
Fristedt U, Weinander R, Martinsson H-S and Persson BL, “Characterisation of purified and unidirectionally reconstituted Pho84 phosphate permease of Saccharomyces cerevisiae”, FEBS Lett. 1999;458;1-5 |
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