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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

HEXIM1 expression is continuously suppressed throughout the entire course of i-CDK9 treatment of five different tumor cell lines.DOI:http://dx.doi.org/10.7554/eLife.06535.009
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fig3s2: HEXIM1 expression is continuously suppressed throughout the entire course of i-CDK9 treatment of five different tumor cell lines.DOI:http://dx.doi.org/10.7554/eLife.06535.009

Mentions: In addition to HeLa cells, a similar biphasic expression pattern was also observed in four other cell lines representing a wide spectrum of human cancers and MYC amplification states (Figure 3A; http://www.broadinstitute.org/ccle/home). Notably, the extent of the initial decrease and then subsequent induction of MYC mRNA production varied among the cell lines. For example, after 2 hr of i-CDK9 (0.5 µM) treatment, the MYC mRNA levels in U87MG (MYC copy number [CN] = 2) and HeLa (CN = 4) cells showed only a slight decrease compared to the DMSO control, whereas they were significantly reduced in A375 (CN = 2), NCIH441 (CN = 8), and A2058 (CN = 4) cells. Furthermore, the prolonged treatment for 8–16 hr caused the MYC mRNA to reach levels much higher than those in the control cells in all cell lines except NCIH441 (Figure 3A). Despite these variations, which could well be caused by differences in MYC mRNA stability in difference cell lines, it is clear that the induction of MYC expression in response to prolonged CDK9 inhibition by i-CDK9 is a general phenomenon likely caused by a common mechanism independent of the MYC amplification/expression levels. In contrast to MYC, another short-lived gene HEXIM1, which was previously shown to depend on active CDK9 for expression (He et al., 2006), was continuously suppressed throughout the entire 16 hr of i-CDK9 treatment in all five cell lines (Figure 3—figure supplement 2).


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)

HEXIM1 expression is continuously suppressed throughout the entire course of i-CDK9 treatment of five different tumor cell lines.DOI:http://dx.doi.org/10.7554/eLife.06535.009
© Copyright Policy
Related In: Results  -  Collection

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

fig3s2: HEXIM1 expression is continuously suppressed throughout the entire course of i-CDK9 treatment of five different tumor cell lines.DOI:http://dx.doi.org/10.7554/eLife.06535.009
Mentions: In addition to HeLa cells, a similar biphasic expression pattern was also observed in four other cell lines representing a wide spectrum of human cancers and MYC amplification states (Figure 3A; http://www.broadinstitute.org/ccle/home). Notably, the extent of the initial decrease and then subsequent induction of MYC mRNA production varied among the cell lines. For example, after 2 hr of i-CDK9 (0.5 µM) treatment, the MYC mRNA levels in U87MG (MYC copy number [CN] = 2) and HeLa (CN = 4) cells showed only a slight decrease compared to the DMSO control, whereas they were significantly reduced in A375 (CN = 2), NCIH441 (CN = 8), and A2058 (CN = 4) cells. Furthermore, the prolonged treatment for 8–16 hr caused the MYC mRNA to reach levels much higher than those in the control cells in all cell lines except NCIH441 (Figure 3A). Despite these variations, which could well be caused by differences in MYC mRNA stability in difference cell lines, it is clear that the induction of MYC expression in response to prolonged CDK9 inhibition by i-CDK9 is a general phenomenon likely caused by a common mechanism independent of the MYC amplification/expression levels. In contrast to MYC, another short-lived gene HEXIM1, which was previously shown to depend on active CDK9 for expression (He et al., 2006), was continuously suppressed throughout the entire 16 hr of i-CDK9 treatment in all five cell lines (Figure 3—figure supplement 2).

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