HMBA Releases P-TEFb from HEXIM1 and 7SK snRNA via PI3K/Akt and Activates HIV Transcription

Hexamethylene bisacetamide (HMBA) is a potent inducer of cell differentiation and HIV production in chronically infected cells. However, its mechanism of action remains poorly defined. In this study, we demonstrate that HMBA activates transiently the PI3K/Akt pathway, which leads to the phosphorylation of HEXIM1 and the subsequent release of active positive transcription elongation factor b (P-TEFb) from its transcriptionally inactive complex with HEXIM1 and 7SK small nuclear RNA (snRNA). As a result, P-TEFb is recruited to the HIV promoter to stimulate transcription elongation and viral production. Despite the continuous presence of HMBA, the released P-TEFb reassembles rapidly with 7SK snRNA and HEXIM1. In contrast, a mutant HEXIM1 protein that cannot be phosphorylated and released from P-TEFb and 7SK snRNA via the PI3K/Akt pathway antagonizes this HMBA-mediated induction of viral production. Thus, our studies reveal how HIV transcription is induced by HMBA and suggest how modifications in the equilibrium between active and inactive P-TEFb could contribute to cell differentiation

Ovarian carcinoma CDK12 mutations misregulate expression of DNA repair genes via deficient formation and function of the Cdk12/CycK complex

The Cdk12/CycK complex promotes expression of a subset of RNA polymerase II genes, including those of the DNA damage response. CDK12 is among only nine genes with recurrent somatic mutations in high-grade serous ovarian carcinoma. However, the influence of thesemutations on the Cdk12/CycK complex and their link to cancerogenesis remain ill-defined. Here, we show that most mutations prevent formation of the Cdk12/CycK complex, rendering the kinase inactive. By examining the mutations within the Cdk12/CycK structure, we find that they likely provoke structural rearrangements detrimental to Cdk12 activation. Our mRNA expression analysis of the patient samples containing the CDK12 mutations reveals coordinated downregulation of genes critical to the homologous recombination DNA repair pathway. Moreover, we establish that the Cdk12/CycK complex occupies these genes and promotes phosphorylation of RNA polymerase II at Ser2. Accordingly, we demonstrate that the mutant Cdk12 proteins fail to stimulate the faithful DNA double strand break repair via homologous recombination. Together, we provide the molecular basis of how mutated CDK12 ceases to function in ovarian carcinoma. We propose that CDK12 is a tumor suppressor of which the loss-of-function mutations may elicit defects in multiple DNA repair pathways, leading to genomic instability underlying the genesis of the cancer.Peer reviewe

P-TEFb Activation by RBM7 Shapes a Pro-survival Transcriptional Response to Genotoxic Stress

DNA damage response (DDR) involves dramatic transcriptional alterations, the mechanisms of which remain ill defined. Here, we show that following genotoxic stress, the RNA-binding motif protein 7 (RBM7) stimulates RNA polymerase II (Pol II) transcription and promotes cell viability by activating the positive transcription elongation factor b (P-TEFb) via its release from the inhibitory 7SK small nuclear ribonucleoprotein (7SK snRNP). This is mediated by activation of p38MAPK, which triggers enhanced binding of RBM7 with core subunits of 7SK snRNP. In turn, P-TEFb relocates to chromatin to induce transcription of short units, including key DDR genes and multiple classes of non-coding RNAs. Critically, interfering with the axis of RBM7 and P-TEFb provokes cellular hypersensitivity to DNA-damage-inducing agents due to activation of apoptosis. Our work uncovers the importance of stress-dependent stimulation of Pol II pause release, which enables a pro-survival transcriptional response that is crucial for cell fate upon genotoxic insult.Peer reviewe

Distal regulation of alternative splicing by splicing enhancer in equine β-casein intron 1

The complexity of cotranscriptional splicing is reflected in the coordinated interplay between various cis-elements and transacting factors. In this report, we demonstrated that a cis-element in intron 1 of the equine β-casein gene (intronic splicing enhancer 1, ISE1) increases the inclusion of all weak exons in its pre-mRNA. The ISE1 also functioned on a hybrid transcript, which was transcribed from the α-globin promoter, where it increased the inclusion of the human fibronectin EDA exon and the β-casein exon 5. The region of ISE1 necessary for its function included the same sequence as is found in some exonic splicing enhancers. Since the ISE1 influenced the splicing of the entire transcript from intron 1, we propose a model for the cotranscriptional splicing of β-casein mRNA, where the 5′ end of the growing transcript remains associated with the C-terminal domain of RNA polymerase II. Thus, the ISE1 remains in close proximity to the mRNA exit groove throughout transcription and influences all weak exons as soon as they are copied

HIV latency: present knowledge and future directions

International audienceCurrent therapies do not eradicate HIV from infected patients. Indeed, HIV hides in a latent form insensitive to these therapies. Thus, one priority is to eliminate these latent reservoirs. But what mechanisms are responsible for latency and what are the reservoirs of latently infected cells? The present knowledge in terms of HIV latency is still incomplete and current therapeutic strategies fail to eradicate latently infected cells. This article reviews present research and discusses possible future strategies

Transcriptional Interference Antagonizes Proviral Gene Expression to Promote HIV Latency

International audienc

Kapa kazeinski gen (CSN3) pri konju

Kappa casein (K-CN) is milk protein that determines the size and specific function of the casein micelles, and its clevage by chymosine is responsible for milk coagulation. Any variation in gene promoter or coding sequence may change the expression of the gene or amino acid sequence, effecting functional properties of the protein. The mature k-cn is encoded by part of the exon 3 and the entire exon 4. Since exon 3 has 33 bp and exon 4 is 497 bp long, the major part of the protein is encoded by exon 4. In this study we identified two SNPs in exon 1 and two in exon 4 of the horse kappa casein gene(CSN3) and genotyped them in three horse breeds. The nucleotide sequence of the first exon was included in this study due to its possible role in the regulation of the CSN3 expression. Because these polymorphisms were analysed for the first time, we used a reference method (RFLP) or at least two other complementig methods (Bi-PASA/PIRA and ASA-PCR/PIRA), for molecular genetic analysis of above mentioned SNPs. The highest variation in genotype frequencies was present in Slovenian cold blood breed. SNPs in exon 4 cause amino acid (AA) change in the mature product, and may very well render chemical/functional properties of the protein. Analysis of the consequences caused bz changes in AA sequence, bz online avaible program tools, comfirmed our hypothesis.Kapa kazein (K-CN) je mlečni protein, ki določa velikost in specifično funkcijo kazeinskih micel, njegova razgradnja s kimozinom pa je odgovorna za koagulacijo mleka. Sprememba v promotorju ali kodirajoèem področju gena lahko vpliva na njegovo izražanje, oziroma spremeni aminokislinsko zaporedje, s tem pa vpliva na funkcionalnost proteina. Zrel K-CN protein je deloma kodiran z eksonom 3 in s celotnim eksonom 4. Zaporedje eksona 1 smo vključili v raziskavo, ker je moyno, da ima regulatorno vlogo. Ker je ekson 3 dolg 33 baznih parov, ekson 4 pa ima 497 baznih parov, je pretežni del proteina kodiran z eksonom 4. V tej študiji smo izvedli genetsko analizo dveh nukleotidnih zamenjav v eksonu 1 in dveh v eksonu 4 v genu za kapa kazein (CSN3) pri konju in jih genotipizirali pri treh pasmah. Ker ti polimorfizmi se nikoli niso bili analizirani, smo za genetsko molekularno analizo omenjenih polimorfizmov, uporabili referenčno metodo (RFLP) ali vsaj dve drugi dopolnjujoči metodi (Bi-PASA/PIRA in ASA-PCR/PIRA). Največja raznolikost genotipov je bila prisotna pri Slovenski hladnokrvni pasmi. Nukleotidni zamenjavi v eksonu 4 povzročita zamenjavo aminokislin v končnem produktu, kar pa lahko spremeni kemične/fukcionalne lastnosti proteina. Analiza posledic sprememb aminokislinske sekvence, s programi na internetu, je potrdila naso hipotezo

HMBA releases P-TEFb from HEXIM1 and 7SK snRNA via PI3K/Akt and activities HIV transcription

Hexamethylene bisacetamide (HMBA) is a potent inducer of cell differentiation and HIV production in chronically infected cells. However, its mechanism of action remains poorly defined. In this study, we demonstrate that HMBA activates transiently the PI3K/Act pathway, which leads to the phosphorylation of HEXIM1 and the subsequent release of active positive transcription elongation factor b (P-TEFb) from its transcriptionally inactivecomplex with HEXIM1 and 7SK small nuclear RNA (snRNA). As a result, P-TEFb is recruited tothe HIV promotoer to stimulate transcription elongation and viral production. Despite the continuous presence of HMBA, the released P-TEFb reassembles rapidly with 7SK sn RNA and HEXIM1. In contrast, a mutant HEXIM1 protein that cannot be phosphorrylated and released from P-TEFb and 7SK snRNA via the PI3K/Act pathway antagonizes this HMBA-mediated induction of viral production. Thus, our studies reveal how transcription is induced by HMBA and suggest how modifications in the equilibrium between active and inactive P-TEFb could contribute to cell differentiation