Study of the regulation of spindle assembly checkpoint gene cdc20 and its role in genomic instability in Human cancer
IR@IICB: CSIR-Indian Institute of Chemical Biology, Kolkata
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| Title |
Study of the regulation of spindle assembly checkpoint gene cdc20 and
its role in genomic instability in
Human cancer
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| Creator |
Banerjee, Taraswi
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| Subject |
Molecular & Human Genetics
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| Description |
We have also investigated the transcriptional regulation of CDC20 in a normal
dividing cell. Since it has been known that CDC20 is expressed within the cell in a cyclic
manner with a peak in expression during pro-metaphase and the surge decreases by lateanaphase,
we reasoned that there must be a repressive effect on CDC20 throughout the rest
of the cell cycle to maintain its expression just at the basal level. To examine our hypothesis,
we treated cells with HDAC inhibitor Trichostatin A and found release in promoter activity,
indicating HDACs bind and repress the CDC20 promoter. WD40 domain containing proteins
have been implicated to act as transcriptional repressors and CDC20 being one such protein
we examined whether it could regulate its own expression. Interestingly, our studies revealed
that CDC20 could repress its own transcription. Further, we also showed that HDAC2 and
Histone 3 methylation at lysine 9 were involved in this CDC20 mediated regulation of its own
VIII
Summary
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promoter. Domain mapping of the CDC20 protein revealed that the WD40 domain was not
sufficient for this control and that the whole protein is necessary for the transcriptional
repression. The functional implication of this repression was further investigated in a time
course experiment using synchronized cells which indicated that the repression on the
CDC20 promoter by CDC20 itself was released during pro-metaphase when more of CDC20
protein was necessary within the cell to drive the cell from metaphase to anaphase. When
the levels of CDC20 are low in the cell the recruitment of CDC20 to its transcription
repression complex also increased, thereby implicating CDC20 to be one of the controls for
the cyclic expression of the protein. This differential promoter occupancy depending on the
cell cycle stage led us to investigate whether post translational modifications of CDC20 were
responsible in the mechanism. Our studies revealed that ubiquitinated form of CDC20 was
not able to bind to the CDC20 promoter whereas the deubiquitinated form was a strong
repressor for the promoter. This finding was in agreement with the expression pattern and
the promoter occupancy of CDC20, as revealed through our studies. During metaphase
CDC20 is ubiquitinated and is expressed in high amounts in the cell. During this phase we
find very little amount of CDC20 to be bound to its promoter. From anaphase, the CDC20
level decreases within the cell and it is no longer ubiquitinated and we find that the promoter
occupancy of the protein increases remarkably. All these taken together indicate that CDC20
plays a vital role in its own transcription and is capable of modulating its own expression by
differentially regulating its expression in a cell cycle dependent manner. The region of the
CDC20 promoter responsible for binding CDC20 is still under investigation and it would be
an interesting find, since, this is the first study implicating CDC20 in transcriptional regulation.
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| Date |
2009
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| Type |
Thesis
NonPeerReviewed |
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| Format |
application/pdf
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| Identifier |
http://www.eprints.iicb.res.in/13/1/complete_thesis.pdf
Banerjee, Taraswi (2009) Study of the regulation of spindle assembly checkpoint gene cdc20 and its role in genomic instability in Human cancer. PhD thesis, Jadavpur University. |
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| Relation |
http://www.eprints.iicb.res.in/13/
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