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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

The i-CDK9-induced increase in CDK9's binding to the MYC locus is mostly BRD4-dependent.DOI:http://dx.doi.org/10.7554/eLife.06535.017
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fig5s1: The i-CDK9-induced increase in CDK9's binding to the MYC locus is mostly BRD4-dependent.DOI:http://dx.doi.org/10.7554/eLife.06535.017

Mentions: To further probe the molecular basis underlying MYC induction by i-CDK9, we performed the classic ChIP-qPCR analysis to examine the interactions of BRD4, CDK9, total Pol II, and the Ser2-phosphoryalted Pol II with the MYC locus before and after treatment with 0.3 μM i-CDK9 for 8 hr. The first noticeable major change caused by i-CDK9 is the significant increase in BRD4's occupancy across the entire MYC locus (Figure 5A,B), which explains why the MYC induction was highly sensitive to the BRD4 inhibitor JQ1 (Figure 4C) and shBRD4 (Figure 4B). Correlating with this increase and consistent with the i-CDK9-induced BRD4-P-TEFb interaction, there was also significantly elevated CDK9 binding to the MYC locus (Figure 5B). Although the elevation in CDK9 binding was mostly BRD4 dependent (Figure 5—figure supplement 1), the distribution pattern of CDK9 was somewhat different from that of BRD4 (Figure 5B). This difference could be caused by P-TEFb's dissociation from BRD4 and joining the Pol II elongation complex once it is recruited to the MYC chromatin template.10.7554/eLife.06535.016Figure 5.Treatment with i-CDK9 (0.3 μM for 8 hr) increases the levels of P-TEFb, BRD4, total Pol II, Pol II with pSer2 CTD and acetyl-H3/H4 at the MYC locus.


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)

The i-CDK9-induced increase in CDK9's binding to the MYC locus is mostly BRD4-dependent.DOI:http://dx.doi.org/10.7554/eLife.06535.017
© Copyright Policy
Related In: Results  -  Collection

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

fig5s1: The i-CDK9-induced increase in CDK9's binding to the MYC locus is mostly BRD4-dependent.DOI:http://dx.doi.org/10.7554/eLife.06535.017
Mentions: To further probe the molecular basis underlying MYC induction by i-CDK9, we performed the classic ChIP-qPCR analysis to examine the interactions of BRD4, CDK9, total Pol II, and the Ser2-phosphoryalted Pol II with the MYC locus before and after treatment with 0.3 μM i-CDK9 for 8 hr. The first noticeable major change caused by i-CDK9 is the significant increase in BRD4's occupancy across the entire MYC locus (Figure 5A,B), which explains why the MYC induction was highly sensitive to the BRD4 inhibitor JQ1 (Figure 4C) and shBRD4 (Figure 4B). Correlating with this increase and consistent with the i-CDK9-induced BRD4-P-TEFb interaction, there was also significantly elevated CDK9 binding to the MYC locus (Figure 5B). Although the elevation in CDK9 binding was mostly BRD4 dependent (Figure 5—figure supplement 1), the distribution pattern of CDK9 was somewhat different from that of BRD4 (Figure 5B). This difference could be caused by P-TEFb's dissociation from BRD4 and joining the Pol II elongation complex once it is recruited to the MYC chromatin template.10.7554/eLife.06535.016Figure 5.Treatment with i-CDK9 (0.3 μM for 8 hr) increases the levels of P-TEFb, BRD4, total Pol II, Pol II with pSer2 CTD and acetyl-H3/H4 at the MYC locus.

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