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SIRTUIN-2 IS REGULATED BY SERUM RESPONSE FACTOR AND P49/STRAP GENES

ABSTRACT: Abstract Introduction: Serum response factor (SRF) has been implicated in the regulation of cell growth, proliferation and senescence. SRF regulates its target genes by binding to the serum response element (SRE or CArG-box) with “CC(A/T)6GG” sequence. SRF interacts with SRF-binding protein(s), including p49/STRAP (SRFBP1), to co-regulate SRF-target genes. Hypothesis: The CArG-sequence exists not only in cytoskeletal genes but also in other genes. Since p49/STRAP, an SRF-binding protein, alters NAD/NADH ratio and affects histone protein deacetylation, we hypothesized that the CArG-sequence may exist in the promoter of sirtuin genes, and that SIRT2 may be regulated by SRF and p49/STRAP. Methods and Results: Using bioinformatic analysis, we found a classic CArG-box sequence in the promoter of SIRT2 gene (accession no. AC011455). Sequencing analysis of five human DNA samples confirmed that all DNA samples had the same CArG-box sequence. Electrophoretic mobility shift assay showed that SRF protein indeed bound to P32-labeled SIRT2 promoter probe. A luciferase vector containing the SIRT2 promoter was constructed and used for transfection assays. The SIRT2 gene promoter was activated by SRF and myocardin, but repressed by p49/STRAP. Serum starvation also changed SIRT2 mRNA levels. Conclusion: The SRF protein binds to the SIRT2 gene promoter and regulates SIRT2 gene expression, thus the SIRT2 gene is a SRF-target gene. SIRT2 gene is modulated by p49/STRAP and myocardin through interactions with SRF. The age-associated increases in cardiac SRF and p49/STRAP protein levels likely affect SIRT2 gene expression and induce histone protein deacetylation, thereby contributing to SIRT2-mediated aging in the heart.

SUBMITTER: Zhang X

PROVIDER: S-EPMC6185360 | biostudies-literature | 2017 Jun

REPOSITORIES: biostudies-literature

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Project description:BACKGROUND: The phytohormone auxin mediates a stunning array of plant development through the functions of AUXIN RESPONSE FACTORs (ARFs), which belong to transcription factors and are present as a protein family comprising 10-43 members so far identified in different plant species. Plant development is also subject to regulation by TRANSPARENT TESTA GLABRA (TTG) proteins, such as NtTTG2 that we recently characterized in tobacco Nicotiana tabacum. To find the functional linkage between TTG and auxin in the regulation of plant development, we performed de novo assembly of the tobacco transcriptome to identify candidates of NtTTG2-regulated ARF genes. RESULTS: The role of NtTTG2 in tobacco growth and development was studied by analyzing the biological effects of gene silencing and overexpression. The NtTTG2 gene silencing causes repressive effects on vegetative growth, floral anthocyanin synthesis, flower colorization, and seed production. By contrast, the plant growth and development processes are promoted by NtTTG2 overexpression. The growth/developmental function of NtTTG2 associates with differential expression of putative ARF genes identified by de novo assembly of the tobacco transcriptome. The transcriptome contains a total of 54,906 unigenes, including 30,124 unigenes (54.86%) with annotated functions and at least 8,024 unigenes (14.61%) assigned to plant growth and development. The transcriptome also contains 455 unigenes (0.83%) related to auxin responses, including 40 putative ARF genes. Based on quantitative analyses, the expression of the putative genes is either promoted or inhibited by NtTTG2. CONCLUSIONS: The biological effects of the NtTTG2 gene silencing and overexpression suggest that NtTTG2 is an essential regulator of growth and development in tobacco. The effects of the altered NtTTG2 expression on expression levels of putative ARF genes identified in the transcriptome suggest that NtTTG2 functions in relation to ARF transcription factors.

Project description:BackgroundConcentric and eccentric cardiac hypertrophy are associated with pressure and volume overload, respectively, in cardiovascular disease both conferring an increased risk of heart failure. These contrasting forms of hypertrophy are characterized by asymmetrical growth of the cardiac myocyte in mainly width or length, respectively. The molecular mechanisms determining myocyte preferential growth in width versus length remain poorly understood. Identification of the mechanisms governing asymmetrical myocyte growth could provide new therapeutic targets for the prevention or treatment of heart failure.MethodsPrimary adult rat ventricular myocytes, adeno-associated virus (AAV)-mediated gene delivery in mice, and human tissue samples were used to define a regulatory pathway controlling pathological myocyte hypertrophy. Chromatin immunoprecipitation assays with sequencing and precision nuclear run-on sequencing were used to define a transcriptional mechanism.ResultsWe report that asymmetrical cardiac myocyte hypertrophy is modulated by SRF (serum response factor) phosphorylation, constituting an epigenomic switch balancing the growth in width versus length of adult ventricular myocytes in vitro and in vivo. SRF Ser103 phosphorylation is bidirectionally regulated by RSK3 (p90 ribosomal S6 kinase type 3) and PP2A (protein phosphatase 2A) at signalosomes organized by the scaffold protein mAKAPβ (muscle A-kinase anchoring protein β), such that increased SRF phosphorylation activates AP-1 (activator protein-1)-dependent enhancers that direct myocyte growth in width. AAV are used to express in vivo mAKAPβ-derived RSK3 and PP2A anchoring disruptor peptides that block the association of the enzymes with the mAKAPβ scaffold. Inhibition of RSK3 signaling prevents concentric cardiac remodeling induced by pressure overload, while inhibition of PP2A signaling prevents eccentric cardiac remodeling induced by myocardial infarction, in each case improving cardiac function. SRF Ser103 phosphorylation is significantly decreased in dilated human hearts, supporting the notion that modulation of the mAKAPβ-SRF signalosome could be a new therapeutic approach for human heart failure.ConclusionsWe have identified a new molecular switch, namely mAKAPβ signalosome-regulated SRF phosphorylation, that controls a transcriptional program responsible for modulating changes in cardiac myocyte morphology that occur secondary to pathological stressors. Complementary AAV-based gene therapies constitute rationally-designed strategies for a new translational modality for heart failure.

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SIRTUIN-2 IS REGULATED BY SERUM RESPONSE FACTOR AND P49/STRAP GENES

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