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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

i-CDK9 does not affect the cellular levels of acetylated histones H3 and H4.DOI:http://dx.doi.org/10.7554/eLife.06535.019
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fig5s3: i-CDK9 does not affect the cellular levels of acetylated histones H3 and H4.DOI:http://dx.doi.org/10.7554/eLife.06535.019

Mentions: Finally, while the levels of acetylated histones H3 (Ac-H3) and H4 (Ac-H4) in whole cell extracts remained unchanged upon exposure to i-CDK9 (Figure 5—figure supplement 3), they were found to increase across the MYC locus especially at locations surrounding the major P1 promoter (Figure 5C). Although the underlying mechanism for this increase is unclear, it explains well the drug-promoted BRD4 binding to the MYC locus. Interestingly, even at early time points of i-CDK9 treatment (0, 1 and 2 hr) when MYC transcription was yet to be induced, the acetylation state of the MYC promoter was already different from that of the HEXIM1 promoter. As shown in Figure 5D, the levels of both Ac-H3 and Ac-H4 at the MYC promoter began to increase at this early stage, with the more robust increase observed for Ac-H4. In contrast, at the HEXIM1 promoter, i-CDK9 caused a drastic decrease in the Ac-H3 level but a small increase of Ac-H4. As for the BRD4 level, it displayed a marked decrease at the MYC promoter at 1 hr post i-CDK9 treatment, but began to rebound by 2 hr. At the HEXIM1 promoter, however, it showed a sustained reduction throughout the entire period (Figure 5D). It is likely that these early differences at the chromatin level predispose a transiently repressed gene such as MYC and a permanently repressed one such as HEXIM1 to completely different expression states later on during the i-CDK9 treatment.


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)

i-CDK9 does not affect the cellular levels of acetylated histones H3 and H4.DOI:http://dx.doi.org/10.7554/eLife.06535.019
© Copyright Policy
Related In: Results  -  Collection

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

fig5s3: i-CDK9 does not affect the cellular levels of acetylated histones H3 and H4.DOI:http://dx.doi.org/10.7554/eLife.06535.019
Mentions: Finally, while the levels of acetylated histones H3 (Ac-H3) and H4 (Ac-H4) in whole cell extracts remained unchanged upon exposure to i-CDK9 (Figure 5—figure supplement 3), they were found to increase across the MYC locus especially at locations surrounding the major P1 promoter (Figure 5C). Although the underlying mechanism for this increase is unclear, it explains well the drug-promoted BRD4 binding to the MYC locus. Interestingly, even at early time points of i-CDK9 treatment (0, 1 and 2 hr) when MYC transcription was yet to be induced, the acetylation state of the MYC promoter was already different from that of the HEXIM1 promoter. As shown in Figure 5D, the levels of both Ac-H3 and Ac-H4 at the MYC promoter began to increase at this early stage, with the more robust increase observed for Ac-H4. In contrast, at the HEXIM1 promoter, i-CDK9 caused a drastic decrease in the Ac-H3 level but a small increase of Ac-H4. As for the BRD4 level, it displayed a marked decrease at the MYC promoter at 1 hr post i-CDK9 treatment, but began to rebound by 2 hr. At the HEXIM1 promoter, however, it showed a sustained reduction throughout the entire period (Figure 5D). It is likely that these early differences at the chromatin level predispose a transiently repressed gene such as MYC and a permanently repressed one such as HEXIM1 to completely different expression states later on during the i-CDK9 treatment.

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