ROLE OF AU-RICH ELEMENT (ARE) BINDING PROTEIN HuR IN POST-TRANSCRIPTIONAL CONTROL OF GENE EXPRESSION IN MAMMALIAN CELLS

Mukherjee, Kamalika (2017) ROLE OF AU-RICH ELEMENT (ARE) BINDING PROTEIN HuR IN POST-TRANSCRIPTIONAL CONTROL OF GENE EXPRESSION IN MAMMALIAN CELLS. PhD thesis, University of Calcutta.

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    Supervisors

    SupervisorsEmail
    Bhattacharyya, Suvendra Nath

    Abstract

    miRNAs, the 22 nucleotide long but stable non-coding RNAs, form miRNP complexes with Argonaute proteins which thereby bind to the 3’UTR of target messages. miRNPs not only cause translational repression of target genes but also destabilize them. During stress, RNA binding protein, HuR, binds to the AU-rich elements of target mRNAs, stabilises them and facilitates their translation. Interestingly, a reduction in cellular miR-122 level of Huh7 cells upon amino acid starvation was observed, with an increase in extracellular vesicle (EV)-associated miR-122 level of starved cells. In this context a new role of ELAV protein HuR was identified. HuR accelerates the EVs-mediated export of miRNAs in human cells. The protein is both necessary and sufficient for the export of corresponding miRNAs. The mechanism behind this phenomenon was studied and it was found that in amino acid starved cells, HuR and miRNPs bind to the common target mRNAs in a mutually exclusive manner. HuR replaces miRNPs from target messages. HuR also reversibly binds with miRNAs and replaces them from Ago2 on endoplasmic reticulum. This HuR-miR-122 binding is specific for miR-122 and in this context and RRMIII of HuR is necessary for this HuRmiRNA binding. In this study it was also found that HuR undergoes ubiquitination on multivesicular bodies (MVBs). This ubiquitination further helps in HuRmiRNA unbinding on MVBs and the resulting HuR-unloaded miRNAs get exported out via EVs. It was known that, the 110 amino acids long segment required for ubiquitination of HuR, spans to its hinge region. Interestingly, the deletion mutant of HuR devoid of hinge region, failed to promote EV-mediated 2 miR-122 export. Therefore, both HuR-miR-122 binding and ubiquitinationmediated release are necessary for HuR-mediated extracellular export of miR122 via EVs. This EV-mediated extracellular export of miRNAs delimits the cellularmiRNA levels not only in starved hepatic cells but also in breast cancer cells and macrophage cells. Therefore, HuR, by modulating extracellular export of miRNAs, controls stress response in amino acid starved Huh7 cells. It further controls cell senescence in MDA-MB-231 breast cancer cells and proinflammatory miRNA levels in RAW 264.7 macrophage like cells.

    Item Type: Thesis (PhD)
    URI: http://www.eprints.iicb.res.in/id/eprint/2770
    Subjects: Molecular & Human Genetics
    Divisions: UNSPECIFIED
    Depositing User: Dr N C Ghosh
    Date Deposited: 18 Jun 2018 14:55
    Last Modified: 18 Jun 2018 14:55
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