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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

MYC induction by 0.3 μM i-CDK9 can be subsequently shut off by 2 μM of the drug.DOI:http://dx.doi.org/10.7554/eLife.06535.014
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fig4s4: MYC induction by 0.3 μM i-CDK9 can be subsequently shut off by 2 μM of the drug.DOI:http://dx.doi.org/10.7554/eLife.06535.014

Mentions: The dependence on catalytically active P-TEFb for MYC induction was further demonstrated by the observation that the initial MYC induction by a low level (e.g., 0.3 μM) of i-CDK9 was subsequently shut off by a higher i-CDK9 concentration (e.g., 2 μM, see Figure 4—figure supplement 4). No MYC induction was detected also when 2 μM i-CDK9 was added into the medium at time zero (see Figure 7A below). Finally, the RNAi-mediated KD of cellular CDK9 and CycT1 levels also completely abolished the i-CDK9-induced MYC expression (Figure 4G). In contrast, KD of CDK12, another reported CTD kinase, failed to prevent i-CDK9 from inducing MYC (Figure 4H). Taken together, these data strongly support the notion that the i-CDK9 induction of MYC expression depends on the enhanced interaction of BRD4 with catalytically active P-TEFb released from 7SK snRNP as well as the binding of the BRD4-P-TEFb complex to acetylated MYC chromatin template.


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)

MYC induction by 0.3 μM i-CDK9 can be subsequently shut off by 2 μM of the drug.DOI:http://dx.doi.org/10.7554/eLife.06535.014
© Copyright Policy
Related In: Results  -  Collection

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

fig4s4: MYC induction by 0.3 μM i-CDK9 can be subsequently shut off by 2 μM of the drug.DOI:http://dx.doi.org/10.7554/eLife.06535.014
Mentions: The dependence on catalytically active P-TEFb for MYC induction was further demonstrated by the observation that the initial MYC induction by a low level (e.g., 0.3 μM) of i-CDK9 was subsequently shut off by a higher i-CDK9 concentration (e.g., 2 μM, see Figure 4—figure supplement 4). No MYC induction was detected also when 2 μM i-CDK9 was added into the medium at time zero (see Figure 7A below). Finally, the RNAi-mediated KD of cellular CDK9 and CycT1 levels also completely abolished the i-CDK9-induced MYC expression (Figure 4G). In contrast, KD of CDK12, another reported CTD kinase, failed to prevent i-CDK9 from inducing MYC (Figure 4H). Taken together, these data strongly support the notion that the i-CDK9 induction of MYC expression depends on the enhanced interaction of BRD4 with catalytically active P-TEFb released from 7SK snRNP as well as the binding of the BRD4-P-TEFb complex to acetylated MYC chromatin template.

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