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Compensatory induction of MYC expression by sustained CDK9 inhibition via a BRD4-dependent mechanism.

Lu H, Xue Y, Xue Y, Yu GK, Arias C, Lin J, Fong S, Faure M, Weisburd B, Ji X, Mercier A, Sutton J, Luo K, Gao Z, Zhou Q - Elife (2015)

Bottom Line: Here, we describe the development of i-CDK9 as such an inhibitor that potently suppresses CDK9 phosphorylation of substrates and causes genome-wide Pol II pausing.While most genes experience reduced expression, MYC and other primary response genes increase expression upon sustained i-CDK9 treatment.Essential for this increase, the bromodomain protein BRD4 captures P-TEFb from 7SK snRNP to deliver to target genes and also enhances CDK9's activity and resistance to inhibition.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States.

ABSTRACT
CDK9 is the kinase subunit of positive transcription elongation factor b (P-TEFb) that enables RNA polymerase (Pol) II's transition from promoter-proximal pausing to productive elongation. Although considerable interest exists in CDK9 as a therapeutic target, little progress has been made due to lack of highly selective inhibitors. Here, we describe the development of i-CDK9 as such an inhibitor that potently suppresses CDK9 phosphorylation of substrates and causes genome-wide Pol II pausing. While most genes experience reduced expression, MYC and other primary response genes increase expression upon sustained i-CDK9 treatment. Essential for this increase, the bromodomain protein BRD4 captures P-TEFb from 7SK snRNP to deliver to target genes and also enhances CDK9's activity and resistance to inhibition. Because the i-CDK9-induced MYC expression and binding to P-TEFb compensate for P-TEFb's loss of activity, only simultaneously inhibiting CDK9 and MYC/BRD4 can efficiently induce growth arrest and apoptosis of cancer cells, suggesting the potential of a combinatorial treatment strategy.

No MeSH data available.


Related in: MedlinePlus

DOI:http://dx.doi.org/10.7554/eLife.06535.024
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fig8: DOI:http://dx.doi.org/10.7554/eLife.06535.024

Mentions: Because CDK9 and BRD4 were recognized by their own specific antibodies in the ChIP assay, the somewhat bigger increase of the CDK9 signal compared to that of BRD4 may simply reflect the different dynamic ranges of recognition or sensitivities of the two antibodies. Based on the reviewer’s suggestion, we have plotted the pSer2/total Pol II ratios across the MYC locus under the DMSO and i-CDK9 conditions and the result is shown in Author response image 1. The ratio is uniformly higher across the entire MYC locus except for the extreme 3’ position (K) following the treatment with 0.3 mM i-CDK9 for 8 hr. This is consistent with the enhanced occupancy of the BRD4-P-TEFb complex at the locus and elevated transcriptional elongation under these conditions. However, no obvious shift of pSer2 toward the 5’ end was detected in the plot.10.7554/eLife.06535.024Author response image 1.


Compensatory induction of MYC expression by sustained CDK9 inhibition via a BRD4-dependent mechanism.

Lu H, Xue Y, Xue Y, Yu GK, Arias C, Lin J, Fong S, Faure M, Weisburd B, Ji X, Mercier A, Sutton J, Luo K, Gao Z, Zhou Q - Elife (2015)

DOI:http://dx.doi.org/10.7554/eLife.06535.024
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4490784&req=5

fig8: DOI:http://dx.doi.org/10.7554/eLife.06535.024
Mentions: Because CDK9 and BRD4 were recognized by their own specific antibodies in the ChIP assay, the somewhat bigger increase of the CDK9 signal compared to that of BRD4 may simply reflect the different dynamic ranges of recognition or sensitivities of the two antibodies. Based on the reviewer’s suggestion, we have plotted the pSer2/total Pol II ratios across the MYC locus under the DMSO and i-CDK9 conditions and the result is shown in Author response image 1. The ratio is uniformly higher across the entire MYC locus except for the extreme 3’ position (K) following the treatment with 0.3 mM i-CDK9 for 8 hr. This is consistent with the enhanced occupancy of the BRD4-P-TEFb complex at the locus and elevated transcriptional elongation under these conditions. However, no obvious shift of pSer2 toward the 5’ end was detected in the plot.10.7554/eLife.06535.024Author response image 1.

Bottom Line: Here, we describe the development of i-CDK9 as such an inhibitor that potently suppresses CDK9 phosphorylation of substrates and causes genome-wide Pol II pausing.While most genes experience reduced expression, MYC and other primary response genes increase expression upon sustained i-CDK9 treatment.Essential for this increase, the bromodomain protein BRD4 captures P-TEFb from 7SK snRNP to deliver to target genes and also enhances CDK9's activity and resistance to inhibition.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, United States.

ABSTRACT
CDK9 is the kinase subunit of positive transcription elongation factor b (P-TEFb) that enables RNA polymerase (Pol) II's transition from promoter-proximal pausing to productive elongation. Although considerable interest exists in CDK9 as a therapeutic target, little progress has been made due to lack of highly selective inhibitors. Here, we describe the development of i-CDK9 as such an inhibitor that potently suppresses CDK9 phosphorylation of substrates and causes genome-wide Pol II pausing. While most genes experience reduced expression, MYC and other primary response genes increase expression upon sustained i-CDK9 treatment. Essential for this increase, the bromodomain protein BRD4 captures P-TEFb from 7SK snRNP to deliver to target genes and also enhances CDK9's activity and resistance to inhibition. Because the i-CDK9-induced MYC expression and binding to P-TEFb compensate for P-TEFb's loss of activity, only simultaneously inhibiting CDK9 and MYC/BRD4 can efficiently induce growth arrest and apoptosis of cancer cells, suggesting the potential of a combinatorial treatment strategy.

No MeSH data available.


Related in: MedlinePlus