Presentation Title

Targeting topoisomerase I SUMOylation in cancer therapy

Start Date

November 2016

End Date

November 2016

Location

HUB 302-62

Type of Presentation

Poster

Abstract

Topoisomerase I (TOP 1) relieves supercoiled DNA and removes helical constraints in order to facilitate DNA replication and RNA transcription. To do so, it binds to DNA, forming a TOP1-DNA covalent complex that cleaves one DNA strand, passages the other strand, religates the DNA, and releases TOP1. Sometimes, TOP1 can become trapped on the DNA due to an incomplete topoisomerase reaction or by treatment with TOP1 poisons, which are chemotherapeutic drugs to treat metastasized cancers. These trapped TOP1s can block transcription and replication, leading to genome instability and cell death. This damage can be prevented by catalytically suppressing TOP1 at the highly transcribed regions by RECQ5-dependent SUMO modifications at its K391 and K436 residues. In this study, we show a preliminary screening of small molecules that block K391/K436 SUMOylation in order to hypersensitize cells to TOP1 poisons. We have identified two compounds (#9 and #23) to be further tested as a cancer chemotherapeutic agent in combinational therapy. We treated HEK293T cells with either DMSO (control), #9, or #23, then performed a cell fractionation on them to collect whole cell extract (WCE), cytoplasmic (CYT), neoplasm (NE), RNase A sensitive (RNA+), and RNase A resistant (RNA-) fractions. Western blot analysis showed that most of the unmodified TOP1 molecules were found in the closed chromatin RNA- fraction at 100 kD. Also, we found #9 and #23 promoted TOP1 activity, evident from the reduced SUMOylated TOP1 present in the RNA+ fraction at 150 kD. This increase in activity may consequently increase TOP1 trapping and eventually kill the cell, so these two compounds could be potentially developed into a cancer therapy.

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Targeting topoisomerase I SUMOylation in cancer therapy

HUB 302-62

Topoisomerase I (TOP 1) relieves supercoiled DNA and removes helical constraints in order to facilitate DNA replication and RNA transcription. To do so, it binds to DNA, forming a TOP1-DNA covalent complex that cleaves one DNA strand, passages the other strand, religates the DNA, and releases TOP1. Sometimes, TOP1 can become trapped on the DNA due to an incomplete topoisomerase reaction or by treatment with TOP1 poisons, which are chemotherapeutic drugs to treat metastasized cancers. These trapped TOP1s can block transcription and replication, leading to genome instability and cell death. This damage can be prevented by catalytically suppressing TOP1 at the highly transcribed regions by RECQ5-dependent SUMO modifications at its K391 and K436 residues. In this study, we show a preliminary screening of small molecules that block K391/K436 SUMOylation in order to hypersensitize cells to TOP1 poisons. We have identified two compounds (#9 and #23) to be further tested as a cancer chemotherapeutic agent in combinational therapy. We treated HEK293T cells with either DMSO (control), #9, or #23, then performed a cell fractionation on them to collect whole cell extract (WCE), cytoplasmic (CYT), neoplasm (NE), RNase A sensitive (RNA+), and RNase A resistant (RNA-) fractions. Western blot analysis showed that most of the unmodified TOP1 molecules were found in the closed chromatin RNA- fraction at 100 kD. Also, we found #9 and #23 promoted TOP1 activity, evident from the reduced SUMOylated TOP1 present in the RNA+ fraction at 150 kD. This increase in activity may consequently increase TOP1 trapping and eventually kill the cell, so these two compounds could be potentially developed into a cancer therapy.