The effect of molecular crowding on the stability of human c-MYC promoter sequence i-motif at neutral pH

<p>The oncogene c-MYC has guanine-rich and complementary cytosine-rich sequences in its P1 promoter region. The P1 promoter is responsible for over 90% of the c-MYC expression. Downregulation of c-MYC expression represents a novel therapeutic approach to more than 50% of all cancers. A stable...

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Main Author: Cui, Jingjing
Other Authors: Edwin A. Lewis
Format: Others
Language:en
Published: MSSTATE 2013
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Online Access:http://sun.library.msstate.edu/ETD-db/theses/available/etd-07022013-134846/
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spelling ndltd-MSSTATE-oai-library.msstate.edu-etd-07022013-1348462015-03-17T15:54:59Z The effect of molecular crowding on the stability of human c-MYC promoter sequence i-motif at neutral pH Cui, Jingjing Chemistry <p>The oncogene c-MYC has guanine-rich and complementary cytosine-rich sequences in its P1 promoter region. The P1 promoter is responsible for over 90% of the c-MYC expression. Downregulation of c-MYC expression represents a novel therapeutic approach to more than 50% of all cancers. A stable i-motif formed by the c-MYC C-rich sequence would be an attractive target for cancer treatment. We have previously shown that c-MYC promoter sequences can form stable i-motifs in acidic solution (pH 4.5-5.5). The question is whether c-MYC promoter sequence i-motif will be stable at physiological pH. </p> <p> In this work, we have investigated the stability of mutant c-MYC i-motif in solutions having pH values from 4 to 7 and containing co-solutes or molecular crowding agents. The crowded nuclear environment was modeled by the addition of polyethylene glycol (PEG, having molecular weights from 200 to 12000 g/mol) at concentrations of 10% to 40% w/w. </p> <p> Circular dichroism spectroscopy (CD) and differential scanning calorimetry (DSC) were used to establish the presence and stability of c-MYC i-motifs in buffer solutions having pH values of 4 to 7. The results of these studies are: 1) the addition of up to 20% w/w glycerol does not increase i-motif stability, 2) the addition of 30% PEG results in an increase in i-motif stability to pH values as high as 6.7, 3) i-motif stability is increased with increased PEG concentration and increased PEG molecular weight, and 4) the effects of PEG size and concentration are not linear, with larger PEGs forming DNA/PEG complexes, which destabilize the i-motif. </p> <p> In summary, we have shown that the c-MYC i-motif can exist as a stable structure at pH as high as 6.7 in a crowded environment. Molecular crowding, largely an excluded volume effect, drives the formation of the more compact i-motif, even at higher pH values where the cytosine imino-nitrogen is deprotonated and neutral C-C pairs can form only two H-bonds. Based on this research, it seems possible that a stable c-MYC promoter sequence i-motif could form at physiological pH and would be a reasonable drug target for new cancer therapies. </p> Edwin A. Lewis Joseph P. Emerson William P. Henry Dongmao Zhang Jiaxu Li MSSTATE 2013-07-30 text application/pdf http://sun.library.msstate.edu/ETD-db/theses/available/etd-07022013-134846/ http://sun.library.msstate.edu/ETD-db/theses/available/etd-07022013-134846/ en unrestricted I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, Dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to Mississippi State University Libraries or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, Dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, Dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, Dissertation, or project report.
collection NDLTD
language en
format Others
sources NDLTD
topic Chemistry
spellingShingle Chemistry
Cui, Jingjing
The effect of molecular crowding on the stability of human c-MYC promoter sequence i-motif at neutral pH
description <p>The oncogene c-MYC has guanine-rich and complementary cytosine-rich sequences in its P1 promoter region. The P1 promoter is responsible for over 90% of the c-MYC expression. Downregulation of c-MYC expression represents a novel therapeutic approach to more than 50% of all cancers. A stable i-motif formed by the c-MYC C-rich sequence would be an attractive target for cancer treatment. We have previously shown that c-MYC promoter sequences can form stable i-motifs in acidic solution (pH 4.5-5.5). The question is whether c-MYC promoter sequence i-motif will be stable at physiological pH. </p> <p> In this work, we have investigated the stability of mutant c-MYC i-motif in solutions having pH values from 4 to 7 and containing co-solutes or molecular crowding agents. The crowded nuclear environment was modeled by the addition of polyethylene glycol (PEG, having molecular weights from 200 to 12000 g/mol) at concentrations of 10% to 40% w/w. </p> <p> Circular dichroism spectroscopy (CD) and differential scanning calorimetry (DSC) were used to establish the presence and stability of c-MYC i-motifs in buffer solutions having pH values of 4 to 7. The results of these studies are: 1) the addition of up to 20% w/w glycerol does not increase i-motif stability, 2) the addition of 30% PEG results in an increase in i-motif stability to pH values as high as 6.7, 3) i-motif stability is increased with increased PEG concentration and increased PEG molecular weight, and 4) the effects of PEG size and concentration are not linear, with larger PEGs forming DNA/PEG complexes, which destabilize the i-motif. </p> <p> In summary, we have shown that the c-MYC i-motif can exist as a stable structure at pH as high as 6.7 in a crowded environment. Molecular crowding, largely an excluded volume effect, drives the formation of the more compact i-motif, even at higher pH values where the cytosine imino-nitrogen is deprotonated and neutral C-C pairs can form only two H-bonds. Based on this research, it seems possible that a stable c-MYC promoter sequence i-motif could form at physiological pH and would be a reasonable drug target for new cancer therapies. </p>
author2 Edwin A. Lewis
author_facet Edwin A. Lewis
Cui, Jingjing
author Cui, Jingjing
author_sort Cui, Jingjing
title The effect of molecular crowding on the stability of human c-MYC promoter sequence i-motif at neutral pH
title_short The effect of molecular crowding on the stability of human c-MYC promoter sequence i-motif at neutral pH
title_full The effect of molecular crowding on the stability of human c-MYC promoter sequence i-motif at neutral pH
title_fullStr The effect of molecular crowding on the stability of human c-MYC promoter sequence i-motif at neutral pH
title_full_unstemmed The effect of molecular crowding on the stability of human c-MYC promoter sequence i-motif at neutral pH
title_sort effect of molecular crowding on the stability of human c-myc promoter sequence i-motif at neutral ph
publisher MSSTATE
publishDate 2013
url http://sun.library.msstate.edu/ETD-db/theses/available/etd-07022013-134846/
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