Article

Controlling the Elongation Phase of Transcription with P-TEFb

Department of Medicine, Microbiology and Immunology, Rosalind Russell Medical Research Center, University of California, San Francisco, San Francisco, California 94143, USA.
Molecular Cell (Impact Factor: 14.02). 09/2006; 23(3):297-305. DOI: 10.1016/j.molcel.2006.06.014
Source: PubMed

ABSTRACT

The positive transcription elongation factor b (P-TEFb) is a cyclin-dependent kinase that controls the elongation phase of transcription by RNA polymerase II (RNAPII). This process is made possible by the reversal of effects of negative elongation factors that include NELF and DSIF. In complex organisms, elongation control is critical for the regulated expression of most genes. In those organisms, the function of P-TEFb is influenced negatively by HEXIM proteins and 7SK snRNA and positively by a variety of recruiting factors. Phylogenetic analyses of the components of the human elongation control machinery indicate that the number of mechanisms utilized to regulate P-TEFb function increased as organisms developed more complex developmental patterns.

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    • "The paused Pol II elongation complex is proposed to serve as a temporal window for the recruitment of additional transcription factors and to allow well-regulated gene expression (Boettiger and Levine, 2009; Gilchrist et al., 2010; Henriques et al., 2013; Smith and Shilatifard, 2013). The transition from stalling to productive elongation requires the recruitment of cyclin-dependent kinase 9 (CDK9) containing positive transcription elongation factor b (P-TEFb) (Marshall et al., 1996), which phosphorylates DSIF, NELF, and the RPB1 CTD tail at serine 2, leading to the removal of NELF and switching DSIF from a negative to a positive elongation factor (Lin et al., 2010; Peterlin and Price, 2006; Smith and Shilatifard, 2013). Accordingly, blocking P-TEFb kinase activity with the CDK9 inhibitor flavopiridol inhibits release of paused Pol II into productive elongation (Rahl et al., 2010), but has no effect on elongating Pol II that is already in gene bodies (Jonkers et al., 2014). "
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    • "Accordingly, we found higher recruitment of P-TEFb to the HIV-1 LTR following cocaine treatment. The role of P-TEFb in facilitating the elongation phase of HIV-1 transcription is well established (Bourgeois et al., 2002; Fujinaga et al., 2004; Ivanov et al., 2000; Karn, 2011; Kim et al., 2002; Parada and Roeder, 1996; Peterlin and Price, 2006; Wei et al., 1998). Hence, our results demonstrate that cocaine enhances HIV-1 gene expression by inducing both the initiation and elongation phases of HIV-1 transcription by activating NF-ĸB and MSK1. "
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    ABSTRACT: Cocaine accelerates human immunodeficiency virus (HIV-1) replication by altering specific cell-signaling and epigenetic pathways. We have elucidated the underlying molecular mechanisms through which cocaine exerts its effect in myeloid cells, a major target of HIV-1 in central nervous system (CNS). We demonstrate that cocaine treatment promotes HIV-1 gene expression by activating both nuclear factor-kappa B (NF-ĸB) and mitogen- and stress-activated kinase 1 (MSK1). MSK1 subsequently catalyzes the phosphorylation of histone H3 at serine 10, and p65 subunit of NF-ĸB at 276th serine residue. These modifications enhance the interaction of NF-ĸB with P300 and promote the recruitment of the positive transcription elongation factor b (P-TEFb) to the HIV-1 LTR, supporting the development of an open/relaxed chromatin configuration, and facilitating the initiation and elongation phases of HIV-1 transcription. Results are also confirmed in primary monocyte derived macrophages (MDM). Overall, our study provides detailed insights into cocaine-driven HIV-1 transcription and replication. Copyright © 2015 Elsevier Inc. All rights reserved.
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    • "We therefore asked if the active subunit of the positive transcription elongation factor P-TEFb, CDK9, was recruited to p21 and puma genes. CDK9 phosphorylates the CTD of RNA Pol II primarily at serine on position two (serine 2) of its heptapeptide sequence, thereby transitioning the transcription machinery into productive transcriptional elongation[55]. Using chromatin immunoprecipitation analysis, we observed that ML-1, MANCA and A875 cell lines had comparable CDK9 recruitment at p21 and puma transcription start sites (TSS) after DNA damage (Figure 4A). This indicated that CDK9 was available to promote transcription elongation. "
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