Increased association of 7SK snRNA with Tat cofactor P-TEFb following activation of peripheral blood lymphocytes

Haaland, Richard E.; Herrmann, Christine; Rice, Andrew P.

doi:10.1097/00002030-200311210-00004

Cited by 37 publications

(44 citation statements)

References 24 publications

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“…The low expression level of HEXIM1 in these cells appears to play a role in the low level of P-TEFb found associated in the 7SK RNP. Our results are in agreement with previous studies where we reported that little P-TEFb can be found associated in the 7SK snRNA-HEXIM1 complex in resting PBLs (peripheral blood lymphocytes) and resting CD4 ϩ T cells; upon activation of the PBLs or resting CD4 ϩ T cells, we observed a large increase in the level of P-TEFb associated with 7SK snRNA and HEXIM1 (49). It is therefore unlikely that association of P-TEFb in the 7SK RNP complex is a mechanism that drives the establishment and maintenance of latency in resting memory CD4 ϩ T cells.…”

Section: Fig 6 In Resting Cd4supporting

confidence: 93%

Cyclin T1 and CDK9 T-Loop Phosphorylation Are Downregulated during Establishment of HIV-1 Latency in Primary Resting Memory CD4⁺T Cells

Budhiraja

Famiglietti

Bosque

et al. 2013

J Virol

109

110

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c P-TEFb, a cellular kinase composed of Cyclin T1 and CDK9, is essential for processive HIV-1 transcription. P-TEFb activity is dependent on phosphorylation of Thr186 in the CDK9 T loop. In resting CD4؉ T cells which are nonpermissive for HIV-1 replication, the levels of Cyclin T1 and T-loop-phosphorylated CDK9 are very low but increase significantly upon cellular activation. Little is known about how P-TEFb activity and expression are regulated in resting central memory CD4؉ T cells, one of the main reservoirs of latent HIV-1. We used an in vitro primary cell model of HIV-1 latency to show that P-TEFb availability in resting memory CD4؉ T cells is governed by the differential expression and phosphorylation of its subunits. This is in contrast to previous observations in dividing cells, where P-TEFb can be regulated by its sequestration in the 7SK RNP complex. We find that resting CD4؉ T cells, whether naïve or memory and independent of their infection status, have low levels of Cyclin T1 and Tloop-phosphorylated CDK9, which increase upon activation. We also show that the decrease in Cyclin T1 protein upon the acquisition of a memory phenotype is in part due to proteasome-mediated proteolysis and likely also to posttranscriptional downregulation by miR-150. We also found that HEXIM1 levels are very low in ex vivo-and in vitro-generated resting memory CD4 ؉ T cells, thus limiting the sequestration of P-TEFb in the 7SK RNP complex, indicating that this mechanism is unlikely to be a driver of viral latency in this cell type.

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Section: Fig 6 In Resting Cd4supporting

confidence: 93%

Cyclin T1 and CDK9 T-Loop Phosphorylation Are Downregulated during Establishment of HIV-1 Latency in Primary Resting Memory CD4⁺T Cells

Budhiraja

Famiglietti

Bosque

et al. 2013

J Virol

109

110

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“…Finally, the observation that overexpression of 7SK snRNA can inhibit Pol II transcription from the P-TEFb-dependent SV40 promoter indicates that 7SK, contrary to previous belief, is limiting for the formation of the 7SK/HEXIM1/P-TEFb complex. This is an unexpected finding, since 7SK is present in the nucleus in great excess compared to HEXIM1 and P-TEFb and only about 30% of 7SK is associated with HEXIM1 and P-TEFb (12). An interpretation of these results is that the major portion of 7SK is sequestered into another RNP complex, which prevents its interaction with HEXIM1 and/or PTEFb.…”

Section: Discussionmentioning

confidence: 89%

Regulation of Polymerase II Transcription by 7SK snRNA: Two Distinct RNA Elements Direct P-TEFb and HEXIM1 Binding

Egloff

Herreweghe

Kiss

2006

Molecular and Cellular Biology

117

183

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The positive transcription elongation factor b (P-TEFb), a complex of Cdk9 and cyclin T1/T2, stimulates transcription by phosphorylating RNA polymerase II. The 7SK small nuclear RNA, in cooperation with HEXIM1 protein, functions as a general polymerase II transcription regulator by sequestering P-TEFb into a large kinase-inactive 7SK/HEXIM1/P-TEFb complex. Here, determination and characterization of the functionally essential elements of human 7SK snRNA directing HEXIM1 and P-TEFb binding led to a new model for the assembly of the 7SK/HEXIM1/P-TEFb regulatory complex. We demonstrate that two structurally and functionally distinct protein binding elements located in the 5-and 3-terminal hairpins of 7SK support the in vivo recruitment of HEXIM1 and P-TEFb. Consistently, a minimal regulatory RNA composed of the 5 and 3 hairpins of 7SK can modulate polymerase II transcription in HeLa cells. HEXIM1 binds independently and specifically to the G24-C48/G60-C87 distal segment of the 5 hairpin of 7SK. Binding of HEXIM1 is a prerequisite for association of P-TEFb with the G302-C324 apical region of the 3 hairpin of 7SK that is highly reminiscent of the human immunodeficiency virus transactivation-responsive RNA.Cyclic phosphorylation of the tandemly repeated YSPTSPS heptapeptide motif in the carboxy-terminal domain (CTD) of the largest subunit of RNA polymerase II (Pol II) is crucial for stimulating mRNA production (9, 14). For example, during the early stage of transcription, phosporylation of the CTD at serine 2 by the positive transcription elongation factor b (PTEFb) is essential for the transition from abortive to productive transcription elongation (5,7,30,35). P-TEFb is a general transcription factor that facilitates the production of fulllength mRNAs of most, if not all, protein-coding genes and also stimulates the Pol II-mediated synthesis of human immunodeficiency virus (HIV) transcripts from the 5Ј long terminal repeat of the integrated proviral genome (5, 29). P-TEFb is composed of a cyclin-dependent kinase, Cdk9, and the regulatory subunit cyclin (Cyc) T1, T2, or K (22, 33, 41; reviewed in reference 23). In human HeLa cells, about half of P-TEFb is associated with large ribonucleoprotein (RNP) complexes which also contain the 7SK small nuclear RNA (snRNA) and the HEXIM1 or HEXIM2 protein (3,17,20,36,37,39). In contrast to its free form, the 7SK/HEXIM1-associated fraction of P-TEFb shows little CTD kinase activity, indicating that the 7SK snRNA, in collaboration with HEXIM1, functions as an inhibitory factor of P-TEFb. Association of P-TEFb with 7SK/HEXIM1 is specific and reversible. Inhibition of transcription by chemical or UV treatment induces dissociation of P-TEFb from the kinase-inactive 7SK/ HEXIM1/P-TEFb complex (17,20,36,37). Consequently, increased accumulation of free P-TEFb facilitates CTD phosphorylation and mRNA production. Likewise, depletion of 7SK snRNA increases the CTD kinase activity of P-TEFb and stimulates transcription from Pol II-specific promoters, including the HIV long terminal repeat...

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“…Moreover, the P-TEFb distribution in a given cell type may also change according to its growth and differentiation status. For example, in quiescent peripheral blood lymphocytes (PBL), where transcriptional demand is low, the level of functional P-TEFb is kept very low through the suppression of CycT1 expression (33). Under these conditions, the expression of HEXIM1 is also very low (34), as there is no excessive P-TEFb activity that must be suppressed at this moment.…”

Section: Cells Strive To Maintain a Delicate Balance Between The Actimentioning

confidence: 99%

“…However, upon the activation of PBL, the level of CycT1 is rapidly induced, which results in an accumulation of functional P-TEFb. At the same time, the levels of HEIXM1 and 7SK are also up-regulated to allow formation of the 7SK snRNP (33). The simultaneous up-regulation of 7SK and HEXIM1 as the P-TEFb level increases in activated PBL suggests that once a fine balance between supply and demand for active P-TEFb is established in the cell, the P-TEFb activity is immediately kept under tight control by the opposing effects of 7SK/HEXIM1 and Brd4 to avoid excessive transcriptional activity.…”

Section: Cells Strive To Maintain a Delicate Balance Between The Actimentioning

confidence: 99%

The Yin and Yang of P-TEFb Regulation: Implications for Human Immunodeficiency Virus Gene Expression and Global Control of Cell Growth and Differentiation

Zhou

Yik

2006

Microbiol Mol Biol Rev

239

287

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SUMMARY The positive transcription elongation factor b (P-TEFb) stimulates transcriptional elongation by phosphorylating the carboxy-terminal domain of RNA polymerase II and antagonizing the effects of negative elongation factors. Not only is P-TEFb essential for transcription of the vast majority of cellular genes, but it is also a critical host cellular cofactor for the expression of the human immunodeficiency virus (HIV) type 1 genome. Given its important role in globally affecting transcription, P-TEFb's activity is dynamically controlled by both positive and negative regulators in order to achieve a functional equilibrium in sync with the overall transcriptional demand as well as the proliferative state of cells. Notably, this equilibrium can be shifted toward either the active or inactive state in response to diverse physiological stimuli that can ultimately affect the cellular decision between growth and differentiation. In this review, we examine the mechanisms by which the recently identified positive (the bromodomain protein Brd4) and negative (the noncoding 7SK small nuclear RNA and the HEXIM1 protein) regulators of P-TEFb affect the P-TEFb-dependent transcriptional elongation. We also discuss the consequences of perturbations of the dynamic associations of these regulators with P-TEFb in relation to the pathogenesis and progression of several major human diseases, such as cardiac hypertrophy, breast cancer, and HIV infection.

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Increased association of 7SK snRNA with Tat cofactor P-TEFb following activation of peripheral blood lymphocytes

Cited by 37 publications

References 24 publications

Cyclin T1 and CDK9 T-Loop Phosphorylation Are Downregulated during Establishment of HIV-1 Latency in Primary Resting Memory CD4⁺T Cells

Cyclin T1 and CDK9 T-Loop Phosphorylation Are Downregulated during Establishment of HIV-1 Latency in Primary Resting Memory CD4⁺T Cells

Regulation of Polymerase II Transcription by 7SK snRNA: Two Distinct RNA Elements Direct P-TEFb and HEXIM1 Binding

The Yin and Yang of P-TEFb Regulation: Implications for Human Immunodeficiency Virus Gene Expression and Global Control of Cell Growth and Differentiation

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Increased association of 7SK snRNA with Tat cofactor P-TEFb following activation of peripheral blood lymphocytes

Cited by 37 publications

References 24 publications

Cyclin T1 and CDK9 T-Loop Phosphorylation Are Downregulated during Establishment of HIV-1 Latency in Primary Resting Memory CD4+T Cells

Cyclin T1 and CDK9 T-Loop Phosphorylation Are Downregulated during Establishment of HIV-1 Latency in Primary Resting Memory CD4+T Cells

Regulation of Polymerase II Transcription by 7SK snRNA: Two Distinct RNA Elements Direct P-TEFb and HEXIM1 Binding

The Yin and Yang of P-TEFb Regulation: Implications for Human Immunodeficiency Virus Gene Expression and Global Control of Cell Growth and Differentiation

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Product

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Cyclin T1 and CDK9 T-Loop Phosphorylation Are Downregulated during Establishment of HIV-1 Latency in Primary Resting Memory CD4⁺T Cells

Cyclin T1 and CDK9 T-Loop Phosphorylation Are Downregulated during Establishment of HIV-1 Latency in Primary Resting Memory CD4⁺T Cells