Mechanistic Analysis of the Role of Bromodomain-Containing Protein 4 (BRD4) in the BRD4-NUT Oncoprotein Induced Transcriptional Activation [Gene Regulation]

December 15th, 2014 by Wang, R., You, J.

NUT midline carcinoma (NMC) is a rare but highly aggressive cancer typically caused by the translocation t(15;19), which results in the formation of BRD4-NUT fusion oncoprotein. Previous studies have demonstrated that fusion of NUT protein with the double bromodomains of BRD4 may significantly alter cellular gene expression profile to contribute to NMC tumorigenesis. However, the mechanistic details of this BRD4-NUT function remains poorly understood. In this study, we examined the NUT function in transcriptional regulation by targeting it to a LacO transgene array integrated in U2OS 2-6-3 cells, which allow us to visualize how NUT alters in situ gene transcription dynamic. Using this system, we demonstrated that NUT protein tethered to the LacO locus recruits p300/CBP, induces histone hyperacetylation, and enriches BRD4 to the transgene array chromatin foci. We also discovered that, in BRD4-NUT expressed in NMC cells, the NUT moiety of the fusion protein anchored to chromatin by the double bromodomains also stimulates histone hyperacetylation, which causes BRD4 to bind tighter to chromatin. Consequently, multiple BRD4-interacting factors are recruited to the NUT-associated chromatin locus to activate in situ transgene expression. This gene transcription function was repressed by either expression of a dominant negative inhibitor of the p300-NUT interaction or treatment with (+)-JQ1, which dissociates BRD4 from the LacO chromatin locus. Our data supports a model in which BRD4-NUT-stimulated histone hyperacetylation recruits additional BRD4 and interacting partners to support transcriptional activation, which underlies the BRD4-NUT oncogenic mechanism in NMC.
  • Posted in Journal of Biological Chemistry, Publications
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