title: Bromodomain and extra-terminal (BET) bromodomain inhibition activate transcription via transient release of positive transcription elongation factor b (P-TEFb) from 7SK small nuclear ribonucleoprotein.
abstract: By phosphorylating elongation factors and the C-terminal domain of RNA polymerase II, the positive transcription elongation factor b (P-TEFb) is the critical kinase for transcription elongation and co-transcriptional processing of eukaryotic genes. It exists in inactive small nuclear ribonucleoprotein (7SK snRNP) and active (free P-TEFb) complexes in cells. The P-TEFb equilibrium determines the state of cellular activation, proliferation, and differentiation. Free P-TEFb, which is required for growth, can be recruited to RNA polymerase II via transcription factors, BRD4, or the super elongation complex (SEC). UV light, various signaling cascades, transcriptional blockade, or compounds such as hexamethylene bisacetamide (HMBA), suberoylanilide hydroxamic acid (SAHA), and other histone deacetylase inhibitors lead to a rapid release of free P-TEFb, followed by its reassembly into the 7SK snRNP. As a consequence, transcription of HEXIM1, a critical 7SK snRNP subunit, and HIV is induced. In this study, we found that a bromodomain and extra-terminal (BET) bromodomain inhibitor, JQ1, which inhibits BRD4 by blocking its association with chromatin, also leads to the rapid release of free P-TEFb from the 7SK snRNP. Indeed, JQ1 transiently increased levels of free P-TEFb and BRD4·P-TEFb and SEC·P-TEFb complexes in cells. As a consequence, the levels of HEXIM1 and HIV proteins rose. Importantly, the knockdown of ELL2, a subunit of the SEC, blocked the ability of JQ1 to increase HIV transcription. Finally, the effects of JQ1 and HMBA or SAHA on the P-TEFb equilibrium were cooperative. We conclude that HMBA, SAHA, and JQ1 affect transcription elongation by a similar and convergent mechanism.
authors.affiliation: Department of Medicine, University of California, San Francisco, California 94143-0703, USA.
authors.forename: Koen
authors.initials: K
authors.lastname: Bartholomeeusen
authors.forename: Yanhui
authors.initials: Y
authors.lastname: Xiang
authors.forename: Koh
authors.initials: K
authors.lastname: Fujinaga
authors.forename: B Matija
authors.initials: BM
authors.lastname: Peterlin
mesh_terms: D000081:Acetamides / Q000494:pharmacology; D001381:Azepines / Q000494:pharmacology; D018797:Cell Cycle Proteins; D002460:Cell Line; D055785:Gene Knockdown Techniques; D015497:HIV-1 / Q000235:genetics / Q000378:metabolism; D006801:Humans; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D042925:Positive Transcriptional Elongation Factor B / Q000235:genetics / Q000378:metabolism*; D012319:RNA Polymerase II / Q000235:genetics / Q000378:metabolism*; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D017411:Ribonucleoproteins, Small Nuclear / Q000235:genetics / Q000378:metabolism*; D061805:Transcription Elongation, Genetic; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D035602:Transcriptional Elongation Factors / Q000235:genetics / Q000378:metabolism; D014230:Triazoles / Q000494:pharmacology; D014466:Ultraviolet Rays; D014764:Viral Proteins / Q000235:genetics / Q000378:metabolism; D000092468:Bromodomain Containing Proteins
chemical_list: D000081:Acetamides; D001381:Azepines; D018797:Cell Cycle Proteins; D009687:Nuclear Proteins; D042925:Positive Transcriptional Elongation Factor B; D012319:RNA Polymerase II; D016601:RNA-Binding Proteins; D017411:Ribonucleoproteins, Small Nuclear; D014157:Transcription Factors; D035602:Transcriptional Elongation Factors; D014230:Triazoles; D014764:Viral Proteins; C561695:(+)-JQ1 compound; C441289:BRD4 protein, human; D000092468:Bromodomain Containing Proteins; C447613:ELL2 protein, human; C476123:HEXIM1 protein, human; C014026:hexamethylene bisacetamide