Transcriptional regulation in mitosis and its implications in genomic instability and cancer

Chowdhury, Abhishek (2017) Transcriptional regulation in mitosis and its implications in genomic instability and cancer. PhD thesis, CU.


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    Roychoudhury, Susanta


    Cancer is a multifactorial multistage human disease with the highest morbidity worldwide. Aneuploidy climaxing in genomic instability is a leading hallmark of cancer progression. Alterations in mitotic pathways lead to aneuploidization of human cells. Proper progression of mitosis depends on orderly ubiquitination and subsequent degradation ofvarious mitotic inhibitors. At molecular level, Cdc20 activates E3 ubiquitin ligase Anaphase Promoting Complex/Cyclosome (APC/C) which along with E2 ubiquitin conjugating enzyme, UbcH10, executes the function of mitotic progression. APC/CCDC20 is negatively regulated by spindle assembly checkpoint (SAC) that ensures accurate segregation of chromosomes during mitosis. SAC comprises MAD and BUB family of proteins which sense lack of tension at improperly attached or unattached kinetochores of metaphase chromosomes. Upon prevalence of errors in kinetochore-spindle attachment, SAC assembles at the unattached kinetochores and generates a ―wait anaphase‖ signal. At the molecular level, an activated SAC sequesters Cdc20 into an inhibitory complex known as Mitotic Checkpoint Complex (MCC) which inhibits APC/C and pauses cells in mitosis till the kinetochore attachment errors get rectified. Upon amphitellic kinetochore-spindle attachment, MCC is disassembled by APC/C-UbcH10 mediated ubiquitination following which Cdc20 associates with APC/C and catalyses mitotic progression of cells. UbcH10 thus plays a pivotal role in mitotic regulation. Interestingly, UbcH10 is found to be one of the majorly deregulated proteins in most cancer types with no reported mutation or polymorphisms. Thus functional regulation of UbcH10 through proteasomal degradation is well studied but its transcriptional regulation is scarcely touched upon. The key role of UbcH10 in mitotic progression thus triggers interest in studying its transcriptional regulation in intricate details. Previous work from our lab reported a novel transcriptional regulatory role of Cdc20. Cdc20-APC/C-CBP complex upregulates UbcH10 through E2F1-DP1 heterodimer. E2F1 was observed to regulate UbcH10 expression in cell cycle dependent manner. Interestingly, Retinoblastoma (Rb) was observed to antagonize UbcH10 expresion. Rb and E2F1 exhibited mutually exclusive regulation of UbcH10 in G1 and G2/M phases of cell cycle respectively. Further, deregulated Rb-E2F1 pathway, through altered UbcH10 expression, contributed significantly to premature mitosis culminating in chromosomal errors and genomic instability. We thus explored a new facet of Rb functionality-its role in regulation of mitosis. UBCH10 expression is turned off during G1 phase. Rb, the master tumour suppressor, plays a pivotal role in this respect. Rb mediates its function by suppression of UbcH10 expression in G1 phase through the suppressive E2F family member-E2F4.The dissertation has explored that there is a novel dual suppressive complex involving Rb-E2F4 and DREAM which mediates UBCH10 repression. Rb and E2F4 collaborate to suppress UbcH10 expression through chromatin modifications. The negative control of UbcH10 monitors cellular proliferation which gets significantly enhanced in cancer progression due to inactivation of Rb. We further explored the novel chromatin modifying role of Anaphase promoting complex/Cyclosome(APC/C) .APC/C was found to modulate UbcH10 expression in G2/M phase through alteration in ubiquitination status of histone 2B. .H2B ubiquitination in conjuction with altered H3 acetylation changes the chromatin dynamics .The chromatin alterations hence potentially help in driving the expression of UbcH10 and has strong implications in monitoring of temporal mitotic division of duplicated chromosomes. Thus the thesis aims to explore the mechanistic regulation of mitosis through transcriptional pathwaysusing UbcH10 as a model gene of study.

    Item Type: Thesis (PhD)
    Subjects: Molecular & Human Genetics
    Divisions: Indian Institute of Chemical Biology
    Depositing User: Ms Sutapa Ganguly
    Date Deposited: 08 Mar 2017 15:11
    Last Modified: 08 Mar 2017 15:11

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