Disease relevance of RN7SK

• The 7SK/P-TEFb interaction may serve as a principal control point for the induction of cellular and HIV-1 viral gene expression during stress-related responses [1].
• 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 [2].
• A major portion of nuclear P-TEFb is sequestered and inactivated by the coordinated actions of the 7SK snRNA and the HEXIM1 protein, whose induced dissociation from P-TEFb is crucial for stress-induced transcription and pathogenesis of cardiac hypertrophy [3].
• We have isolated and characterized two recombinant lambda phages containing sequences homologous to 7SK RNA which code for a RNA 330 nucleotides long in an "in vitro" transcription system [4].

High impact information on RN7SK

• RNA polymerase III transcription of adjacent plasmid sequences can be directed by this promoter in the complete absence of the 7SK RNA coding region, indicating that no internal promoter sequences are required [5].
• Cdk9 was limiting for cardiac growth, shown by suppressing its inhibitor (7SK) in culture and preventing downregulation of its activator (cyclin T1) in mouse myocardium.Note: In the AOP version of this article, the numbering of the author affiliations was incorrect [6].
• The 7SK small nuclear RNA inhibits the CDK9/cyclin T1 kinase to control transcription [1].
• 7SK is efficiently dissociated from P-TEFb by treatment of cells with ultraviolet irradiation and actinomycin D [1].
• 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 [7].

Biological context of RN7SK

• Brd4, HEXIM1, and 7SK are all implicated in regulating cell growth, which may result from their dynamic control of the general transcription factor P-TEFb [8].
• Since HEXIM1 expression is induced in cells treated with hexamethylene bisacetamide, a potent inducer of cell differentiation, targeting the general transcription factor P-TEFb by HEXIM1/7SK may contribute to the global control of cell growth and differentiation [9].
• Consistently, point mutations in an evolutionarily conserved motif (aa 202-205) were found to suppress P-TEFb binding and inhibition without affecting 7SK recognition [10].
• 7SK RNA has extensive sequence complementarity to U4 snRNA, within the U4/U6 base pairing domain, and also to U11 snRNA [11].
• 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 [2].

Anatomical context of RN7SK

• In growing HeLa cells, half of P-TEFb is kinase inactive and binds to the 7SK small nuclear RNA [12].
• CONCLUSION: Increased association of 7SK snRNA with P-TEFb in activated lymphocytes correlates with increased global transcription [13].
• OBJECTIVE: This study was undertaken to determine whether 7SK small nuclear RNA (snRNA), which has been proposed to function as an inhibitor of Tat cofactor P-TEFb, plays a role in transcriptional latency in T cells [13].
• The conserved 7SK snRNA gene localizes to human chromosome 6 by homolog exclusion probing of somatic cell hybrid RNA [14].
• DNA binding assays and microinjection of mutant genes into Xenopus oocytes showed the presence of Staf-responsive elements in the genes for human U4C, U6, Y4 and 7SK, Xenopus U1b1, U2, U5 and MRP and mouse U6 RNAs [15].

Associations of RN7SK with chemical compounds

• The large complex is composed of P-TEFb, 7SK small nuclear RNA, and hexamethylene bisacetamide-inducible protein 1 (Hexim1) [16].
• The 3'-terminal adenylic acid residue in several human small RNAs including signal recognition particle (SRP) RNA, nuclear 7SK RNA, U2 small nuclear RNA, and ribosomal 5S RNA is caused by a post-transcriptional adenylation event (Sinha, K., Gu, J., Chen, Y., and Reddy, R. (1998) J. Biol. Chem. 273, 6853-6859) [17].
• In this study, we have used dimethyl sulphate and DNase I treatment of HeLa cells and nuclei, respectively, followed by linker-mediated polymerase chain reaction, to obtain in vivo footprints of proteins binding to the promoter of the Pol III-transcribed 7SK gene [18].
• We describe the development of an inducible siRNA expression system that is based on the tetracycline repressor and eukaryotic RNA polymerase III promoters (U6 and 7SK) [19].

Physical interactions of RN7SK

• It is proposed that 7SK RNA binding to a HEXIM1 multimer promotes the simultaneous recruitment and hence inactivation of multiple P-TEFb units [20].
• Electrophoretic mobility shift assays and in vitro kinase assays demonstrate that HEXIM2 forms complexes containing 7SK and P-TEFb and, in conjunction with 7SK, inhibits P-TEFb kinase activity [21].
• Moreover, the arginine-rich motif within it is essential for its binding to 7SK snRNA, P-TEFb, and inhibition of transcription [22].

Regulatory relationships of RN7SK

• Deletion of the first 121 amino acids of HEXIM1 allowed it to inhibit P-TEFb partially in the absence of 7SK RNA [23].
• Here we show that, like HEXIM1, a highly homologous protein named HEXIM2 also possesses the ability to inactivate P-TEFb to suppress transcription through a 7SK-mediated interaction with P-TEFb [24].

Other interactions of RN7SK

• Inhibition of cellular transcription by chemical agents or ultraviolet irradiation trigger the complete disruption of the P-TEFb/7SK complex, and enhance CDK9 activity [25].
• Inhibition of transcription results in the release of both MAQ1 and 7SK RNA from P-TEFb [12].
• Positive transcription elongation factor b (P-TEFb) regulates eukaryotic gene expression at the level of elongation, and is itself controlled by the reversible association of 7SK RNA and an RNA-binding protein, HEXIM1 or HEXIM2 [23].
• Consistently, a minimal regulatory RNA composed of the 5' and 3' hairpins of 7SK can modulate polymerase II transcription in HeLa cells [2].
• The 7SK-binding motif in HEXIM1 contains clusters of positively charged residues reminiscent of the arginine-rich RNA-binding motif found in a wide variety of proteins [26].
• Through cooperatively dephosphorylating Cdk9 in response to Ca2+ signaling, PP2B and PP1alpha alter the P-TEFb functional equilibrium through releasing P-TEFb from 7SK snRNP for transcription [27].

Analytical, diagnostic and therapeutic context of RN7SK

• We mapped a productive human 7SK small nuclear RNA gene to human chromosome 6 by analyzing Northern blots derived from a panel of somatic cell hybrids that contain single human chromosomes [14].
• The organization of eight small nuclear ribonucleoproteins (the U1, U2, U4, U5, and U6 RNAs previously studied by others and three additional snRNAs, U11, U12, and 7SK) has been investigated in cultured human cells by fluorescence in situ hybridization with antisense DNA and 2'-O-Me RNA oligonucleotides [28].
• Southern blotting using a human 7SK pseudogene probe illuminated a series of multiple restriction fragments in mammalian genomes, with generally fewer fragments in the genomes of birds and reptiles and a single reactive fragment in DNA from terrapin (Pseudemys scripta elegans) and Xenopus laevis (South African clawed toad) [29].
• After an unsuccessful search for the 7SK RNA gene in four mouse genomic libraries, we used the inverse polymerase chain reaction (IPCR) on fractionated genomic DNA to characterize sequences containing complete copies of 7SK plus flanking regions for analysis of putative transcription regulatory sequences [30].

References