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In-Vivo Quantitative Proteomics Reveals a Key Contribution of Post-Transcriptional Mechanisms to the Circadian Regulation of Liver Metabolism  [PDF]
Maria S. Robles,Jürgen Cox,Matthias Mann
PLOS Genetics , 2014, DOI: doi/10.1371/journal.pgen.1004047
Abstract: Circadian clocks are endogenous oscillators that drive the rhythmic expression of a broad array of genes, orchestrating metabolism and physiology. Recent evidence indicates that post-transcriptional and post-translational mechanisms play essential roles in modulating temporal gene expression for proper circadian function, particularly for the molecular mechanism of the clock. Due to technical limitations in large-scale, quantitative protein measurements, it remains unresolved to what extent the circadian clock regulates metabolism by driving rhythms of protein abundance. Therefore, we aimed to identify global circadian oscillations of the proteome in the mouse liver by applying in vivo SILAC mouse technology in combination with state of the art mass spectrometry. Among the 3000 proteins accurately quantified across two consecutive cycles, 6% showed circadian oscillations with a defined phase of expression. Interestingly, daily rhythms of one fifth of the liver proteins were not accompanied by changes at the transcript level. The oscillations of almost half of the cycling proteome were delayed by more than six hours with respect to the corresponding, rhythmic mRNA. Strikingly we observed that the length of the time lag between mRNA and protein cycles varies across the day. Our analysis revealed a high temporal coordination in the abundance of proteins involved in the same metabolic process, such as xenobiotic detoxification. Apart from liver specific metabolic pathways, we identified many other essential cellular processes in which protein levels are under circadian control, for instance vesicle trafficking and protein folding. Our large-scale proteomic analysis reveals thus that circadian post-transcriptional and post-translational mechanisms play a key role in the temporal orchestration of liver metabolism and physiology.
Contribution of transcriptional regulation to natural variations in Arabidopsis
Wenqiong J Chen, Sherman H Chang, Matthew E Hudson, Wai-King Kwan, Jingqiu Li, Bram Estes, Daniel Knoll, Liang Shi, Tong Zhu
Genome Biology , 2005, DOI: 10.1186/gb-2005-6-4-r32
Abstract: Among five accessions (Col-0, C24, Ler, WS-2, and NO-0) 7,508 probe sets with no detectable genomic sequence variations were identified on the basis of the comparative genomic hybridization to the Arabidopsis GeneChip microarray, and used for accession-specific transcriptome analysis. Two-way ANOVA analysis has identified 60 genes whose mRNA levels differed in different accession backgrounds in an organ-dependent manner. Most of these genes were involved in stress responses and late stages of plant development, such as seed development. Correlation analysis of expression patterns of these 7,508 genes between pairs of accessions identified a group of 65 highly plastic genes with distinct expression patterns in each accession.Genes that show substantial genetic variation in mRNA level are those with functions in signal transduction, transcription and stress response, suggesting the existence of variations in the regulatory mechanisms for these genes among different accessions. This is in contrast to those genes with significant polymorphisms in the coding regions identified by genomic hybridization, which include genes encoding transposon-related proteins, kinases and disease-resistance proteins. While relatively fewer sequence variations were detected on average in the coding regions of these genes, a number of differences were identified from the upstream regions, several of which alter potential cis-regulatory elements. Our results suggest that nucleotide polymorphisms in regulatory elements of genes encoding controlling factors could be primary targets of natural selection and a driving force behind the evolution of Arabidopsis accessions.Transcription of mRNA from DNA and subsequent translation of mRNA into protein transform genetic blueprints into cellular functions. This process of gene expression and regulation plays a key role in determining the fitness of the genome, through the production of different proteins in different cells and at different times. Ther
Bridging HIV-1 Cellular Latency and Clinical Long-Term Non-Progressor: An Interactomic View  [PDF]
Jin Yang, Zongxing Yang, Hangjun Lv, Yi Lou, Juan Wang, Nanping Wu
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0055791
Abstract: Development of an effective HIV management is enticed by the fact that long-term non-progressors (LTNP) restrict viral replication spontaneously, but is hindered by HIV-1 latency. Given that the most overlapping characteristics found between HIV-1 LTNP and latency, detailed analysis of the difference would disclose the essentials of latency. In this study, microarray data from our previous study was combined with HIV-1 latency and LTNP data obtained from NCBI GEO database. Principal variance component analysis and hierarchical clustering verified the removal of batch effect across platform. The analysis revealed a total of 456 differential expressed genes with >2-fold change and B-statistic >0. Bayesian inference was used to reconstitute the transcriptional network of HIV-1 latency or LTNP, respectively. Gene regulation was reprogrammed under different disease condition. By network interference, KPNA2 and ATP5G3 were identified as the hubs in latency network which mediate nuclear export and RNA processing. These data offer comparative insights into HIV-1 latency, which will facilitate the understanding of the genetic basis of HIV-1 latency in vivo and serve as a clue for future treatment dealing with key targets in HIV-1 latency.
Mechanisms of post-transcriptional gene regulation in bacterial biofilms  [PDF]
Luary C. Martínez,Viveka Vadyvaloo
Frontiers in Cellular and Infection Microbiology , 2014, DOI: 10.3389/fcimb.2014.00038
Abstract: Biofilms are characterized by a dense multicellular community of microorganisms that can be formed by the attachment of bacteria to an inert surface and to each other. The development of biofilm involves the initial attachment of planktonic bacteria to a surface, followed by replication, cell-to-cell adhesion to form microcolonies, maturation, and detachment. Mature biofilms are embedded in a self-produced extracellular polymeric matrix composed primarily of bacterial-derived exopolysaccharides, specialized proteins, adhesins, and occasionally DNA. Because the synthesis and assembly of biofilm matrix components is an exceptionally complex process, the transition between its different phases requires the coordinate expression and simultaneous regulation of many genes by complex genetic networks involving all levels of gene regulation. The finely controlled intracellular level of the chemical second messenger molecule, cyclic-di-GMP is central to the post-transcriptional mechanisms governing the switch between the motile planktonic lifestyle and the sessile biofilm forming state in many bacteria. Several other post-transcriptional regulatory mechanisms are known to dictate biofilm development and assembly and these include RNA-binding proteins, small non-coding RNAs, toxin-antitoxin systems, riboswitches, and RNases. Post-transcriptional regulation is therefore a powerful molecular mechanism employed by bacteria to rapidly adjust to the changing environment and to fine tune gene expression to the developmental needs of the cell. In this review, we discuss post-transcriptional mechanisms that influence the biofilm developmental cycle in a variety of pathogenic bacteria.
PRDM Proteins: Molecular Mechanisms in Signal Transduction and Transcriptional Regulation  [PDF]
Erika Di Zazzo,Caterina De Rosa,Ciro Abbondanza,Bruno Moncharmont
Biology , 2013, DOI: 10.3390/biology2010107
Abstract: PRDM (PRDI-BF1 and RIZ homology domain containing) protein family members are characterized by the presence of a PR domain and a variable number of Zn-finger repeats. Experimental evidence has shown that the PRDM proteins play an important role in gene expression regulation, modifying the chromatin structure either directly, through the intrinsic methyltransferase activity, or indirectly through the recruitment of chromatin remodeling complexes. PRDM proteins have a dual action: they mediate the effect induced by different cell signals like steroid hormones and control the expression of growth factors. PRDM proteins therefore have a pivotal role in the transduction of signals that control cell proliferation and differentiation and consequently neoplastic transformation. In this review, we describe pathways in which PRDM proteins are involved and the molecular mechanism of their transcriptional regulation.
Transcriptional regulation of cardiac genes balance pro- and anti-hypertrophic mechanisms in hypertrophic cardiomyopathy  [cached]
Nina Genneb?ck,Gerhard Wikstr?m,Urban Hellman,Jane-Lise Samuel
Cardiogenetics , 2012, DOI: 10.4081/cardiogenetics.2012.e5
Abstract: Hypertrophic cardiomyopathy (HCM) is characterized by unexplained left ventricular hypertrophy. HCM is often hereditary, but our knowledge of the mechanisms leading from mutation to phenotype is incomplete. The transcriptional expression patterns in the myocar - dium of HCM patients may contribute to understanding the mechanisms that drive and stabilize the hypertrophy. Cardiac myectomies/biopsies from 8 patients with hypertrophic obstructive cardiomyopathy (HOCM) and 5 controls were studied with whole genome Illumina microarray gene expression (detecting 18 189 mRNA). When comparing HOCM myocardium to controls, there was significant transcriptional down-regulation of the MYH6, EGR1, APOB and FOS genes, and significant transcriptional up-regulation of the ACE2, JAK2, NPPA (ANP), APOA1 and HDAC5 genes. The transcriptional regulation revealed both pro- and anti-hypertrophic mechanisms. The pro-hypertrophic response was explained by the transcriptional down-regulation of MYH6, indicating that the switch to the fetal gene program is maintained, and the transcriptional up-regulation of JAK2 in the JAK-STAT pathway. The anti-hypertrophic response was seen as a transcriptional down-regulation of the immediate early genes (IEGs), FOS and EGR1, and a transcriptional up-regulation of ACE2 and HDAC5. This can be interpreted as a transcriptional endogenous protection system in the heart of the HOCM patients, neither growing nor suppressing the already hypertrophic myocardium.
Lost in Transcription: Molecular Mechanisms that Control HIV Latency  [PDF]
Ran Taube,Matija Peterlin
Viruses , 2013, DOI: 10.3390/v5030902
Abstract: Highly active antiretroviral therapy (HAART) has limited the replication and spread of the human immunodeficiency virus (HIV). However, despite treatment, HIV infection persists in latently infected reservoirs, and once therapy is interrupted, viral replication rebounds quickly. Extensive efforts are being directed at eliminating these cell reservoirs. This feat can be achieved by reactivating latent HIV while administering drugs that prevent new rounds of infection and allow the immune system to clear the virus. However, current approaches to HIV eradication have not been effective. Moreover, as HIV latency is multifactorial, the significance of each of its molecular mechanisms is still under debate. Among these, transcriptional repression as a result of reduced levels and activity of the positive transcription elongation factor b (P-TEFb: CDK9/cyclin T) plays a significant role. Therefore, increasing levels of P-TEFb expression and activity is an excellent strategy to stimulate viral gene expression. This review summarizes the multiple steps that cause HIV to enter into latency. It positions the interplay between transcriptionally active and inactive host transcriptional activators and their viral partner Tat as valid targets for the development of new strategies to reactivate latent viral gene expression and eradicate HIV.
Regulation of Caenorhabditis elegans vitellogenesis by DAF-2/IIS through separable transcriptional and posttranscriptional mechanisms
Ana S DePina, Wendy B Iser, Sung-Soo Park, Stuart Maudsley, Mark A Wilson, Catherine A Wolkow
BMC Physiology , 2011, DOI: 10.1186/1472-6793-11-11
Abstract: In order to identify mechanisms that suppress vitellogenesis under prolongevity conditions, we studied factors regulating vitellogenesis in C. elegans nematodes. In C. elegans, vitellogenesis is depressed in the absence of insulin-like signaling (IIS). We found that the C. elegans daf-2/IIS pathway regulates vitellogenesis through two mechanisms. vit-2 transcript levels in daf-2 mutants were indirectly regulated through a germline-dependent signal, and could be rescued by introduction of daf-2(+) sperm. However, yolk protein (YP) levels in daf-2 mutants were also regulated by germline-independent posttranscriptional mechanisms.C. elegans vitellogenesis is regulated transcriptionally and posttranscriptionally in response to environmental and reproductive cues. The daf-2 pathway suppressed vitellogenesis through transcriptional mechanisms reflecting reproductive phenotypes, as well as distinct posttranscriptional mechanisms. This study reveals that pleiotropic effects of IIS pathway mutations can converge on a common downstream target, vitellogenesis, as a mechanism to modulate longevity.According to evolutionary theories of aging, lifespan evolves as a trade-off between the metabolic costs of somatic maintenance with those of reproduction. Reproductive processes such as egg production and progeny rearing are energy-intense and drain resources away from processes that promote somatic maintenance. Studies have provided evidence for a trade-off between reproduction and survival. For example, experimentally increased egg production in wild seabirds is associated with lower rates of postmigratory return to breeding grounds [1,2]. One mechanism by which organisms can regulate the relative burdens of reproduction and somatic maintenance in response to environmental conditions is through phenotypic plasticity of life-history traits, such as growth and reproduction [3]. Plasticity in life-history traits can affect lifespan directly, such as to delay reproduction until environ
Mechanisms of transcriptional regulation and prognostic significance of activated leukocyte cell adhesion molecule in cancer
Judy A King, Fang Tan, Flaubert Mbeunkui, Zachariah Chambers, Sarah Cantrell, Hairu Chen, Diego Alvarez, Lalita A Shevde, Solomon F Ofori-Acquah
Molecular Cancer , 2010, DOI: 10.1186/1476-4598-9-266
Abstract: A common site for transcription initiation of the ALCAM gene was identified and the ALCAM promoter sequenced. The promoter contains multiple cis-active elements including a functional p65 NF-κB motif, and it harbors an extensive array of CpG residues highly methylated exclusively in ALCAM-negative tumor cells. These CpG residues were modestly demethylated after 5-aza-2-deoxycytidine treatment. Restoration of high-level ALCAM expression using an ALCAM cDNA increased clustering of MDA-MB-435 tumor cells perfused through the pulmonary vasculature of ventilated rat lungs. Anti-ALCAM antibodies reduced the number of intravascular tumor cell clusters.Our data suggests that loss of ALCAM expression, due in part to DNA methylation of extensive segments of the promoter, significantly impairs the ability of circulating tumor cells to adhere to each other, and may therefore promote metastasis. These findings offer insight into the mechanisms for down-regulation of ALCAM gene expression in tumor cells, and for the positive prognostic value of high-level ALCAM in breast cancer.ALCAM/CD166 is an immunoglobulin cell adhesion molecule expressed by neuronal, endothelial, hematopoietic and epithelial cells [1-13]. It's up-regulation in cancer was first identified at the RNA level in melanoma cell lines as memD [14]. Subsequently, increased ALCAM expression was found in melanoma tumors in situ [13,15]. More widespread deregulation of ALCAM expression has since been reported in several other tumors including those of the prostate [16,17], esophagus [18], colon [19], bladder [20] and pancreas [21]. Alterations in ALCAM expression in tumors have recently been reviewed by Ofori-Acquah and King [22].In a study of primary breast cancer tissues and non-neoplastic mammary tissue from the same mastectomies, we discovered that the level of ALCAM transcripts was lower in breast cancer tissues from patients who had metastases to regional lymph nodes [23], and that primary tumors from patients who
Repressive LTR Nucleosome Positioning by the BAF Complex Is Required for HIV Latency  [PDF]
Haleh Rafati,Maribel Parra,Shweta Hakre,Yuri Moshkin,Eric Verdin,Tokameh Mahmoudi
PLOS Biology , 2012, DOI: 10.1371/journal.pbio.1001206
Abstract: Persistence of a reservoir of latently infected memory T cells provides a barrier to HIV eradication in treated patients. Several reports have implicated the involvement of SWI/SNF chromatin remodeling complexes in restricting early steps in HIV infection, in coupling the processes of integration and remodeling, and in promoter/LTR transcription activation and repression. However, the mechanism behind the seemingly contradictory involvement of SWI/SNF in the HIV life cycle remains unclear. Here we addressed the role of SWI/SNF in regulation of the latent HIV LTR before and after transcriptional activation. We determined the predicted nucleosome affinity of the LTR sequence and found a striking reverse correlation when compared to the strictly positioned in vivo LTR nucleosomal structure; sequences encompassing the DNase hypersensitive regions displayed the highest nucleosome affinity, while the strictly positioned nucleosomes displayed lower affinity for nucleosome formation. To examine the mechanism behind this reverse correlation, we used a combinatorial approach to determine DNA accessibility, histone occupancy, and the unique recruitment and requirement of BAF and PBAF, two functionally distinct subclasses of SWI/SNF at the LTR of HIV-infected cells before and after activation. We find that establishment and maintenance of HIV latency requires BAF, which removes a preferred nucleosome from DHS1 to position the repressive nucleosome-1 over energetically sub-optimal sequences. Depletion of BAF resulted in de-repression of HIV latency concomitant with a dramatic alteration in the LTR nucleosome profile as determined by high resolution MNase nucleosomal mapping. Upon activation, BAF was lost from the HIV promoter, while PBAF was selectively recruited by acetylated Tat to facilitate LTR transcription. Thus BAF and PBAF, recruited during different stages of the HIV life cycle, display opposing function on the HIV promoter. Our data point to the ATP-dependent BRG1 component of BAF as a putative therapeutic target to deplete the latent reservoir in patients.
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