Project description:RNA microarray analyses revealed that nuclear actin activated many human transcription factor genes including OCT4, which is required for gene reprogramming. OCT4 is known to be activated by nuclear actin in Xenopus oocytes. Our findings imply that this process of OCT4 activation is conserved in vertebrates and among cell types, and could be used for gene reprogramming of human cells.
Project description:Chavez2009 - a core regulatory network of OCT4 in human embryonic stem cells
A core OCT4-regulated network has been identified as a test case, to analyase stem cell characteristics and cellular differentiation.
This model is described in the article:
In silico identification of a core regulatory network of OCT4 in human embryonic stem cells using an integrated approach.
Chavez L, Bais AS, Vingron M, Lehrach H, Adjaye J, Herwig R
BMC Genomics, 2009, 10:314
Abstract:
BACKGROUND: The transcription factor OCT4 is highly expressed in pluripotent embryonic stem cells which are derived from the inner cell mass of mammalian blastocysts. Pluripotency and self renewal are controlled by a transcription regulatory network governed by the transcription factors OCT4, SOX2 and NANOG. Recent studies on reprogramming somatic cells to induced pluripotent stem cells highlight OCT4 as a key regulator of pluripotency.
RESULTS: We have carried out an integrated analysis of high-throughput data (ChIP-on-chip and RNAi experiments along with promoter sequence analysis of putative target genes) and identified a core OCT4 regulatory network in human embryonic stem cells consisting of 33 target genes. Enrichment analysis with these target genes revealed that this integrative analysis increases the functional information content by factors of 1.3 - 4.7 compared to the individual studies. In order to identify potential regulatory co-factors of OCT4, we performed a de novo motif analysis. In addition to known validated OCT4 motifs we obtained binding sites similar to motifs recognized by further regulators of pluripotency and development; e.g. the heterodimer of the transcription factors C-MYC and MAX, a prerequisite for C-MYC transcriptional activity that leads to cell growth and proliferation.
CONCLUSION: Our analysis shows how heterogeneous functional information can be integrated in order to reconstruct gene regulatory networks. As a test case we identified a core OCT4-regulated network that is important for the analysis of stem cell characteristics and cellular differentiation. Functional information is largely enriched using different experimental results. The de novo motif discovery identified well-known regulators closely connected to the OCT4 network as well as potential new regulators of pluripotency and differentiation. These results provide the basis for further targeted functional studies.
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Project description:Sirtuin1 (Sirt1) in skeletal muscle (SK) and fat protects against metabolic damage by stimulating insulin sensitivity. Here we report that mice with selective deletion of endothelial Sirt1 (E-Sirt1-KO) paradoxically exhibit heightened whole-body insulin sensitivity. Akt phosphorylation, glucose uptake, and glycolysis are boosted in SK and brown adipose tissue (BAT) of E-Sirt1-KO mice. E-Sirt1-KO mice have higher energy expenditure and are partially protected from high-fat diet-induced insulin resistance. Enhanced insulin sensitivity and peripheral tissue Akt phosphorylation in E-Sirt1-KO mice is transferrable to wild-type mice via the systemic circulation after surgical parabiosis. Silencing of Sirt1 in endothelial cells upregulates transcription of the F-actin-binding protein thymosin beta-4 (Tβ4), whose secretion activates Akt in skeletal myotubes. Sirt1 downregulation stimulates endothelial Tβ4 transcription through inhibition of autophagy and upregulation of nuclear factor-kappa B signaling. Thus, unlike Sirt1 in skeletal muscle and fat, endothelial Sirt1 curtails whole-body insulin sensitivity by inhibiting expression of secreted Tβ4
Project description:Nuclear actin participates in many essential cellular processes including gene transcription, chromatic remodelling and mRNA processing. Actin shuttles into and out the nucleus through the action of dedicated transport receptors importin-9 and exportin-6, but how this transport is regulated remains unclear. Here we show that RASSF1A is a novel regulator of actin nucleocytoplasmic trafficking and is required for the active maintenance of nuclear actin levels through supporting binding of exportin-6 (XPO6) to RAN GTPase. RASSF1A (Ras association domain family 1 isoform A) is a tumor suppressor gene frequently silenced by promoter hypermethylation in all major solid cancers. Specifically, we demonstrate that endogenous RASSF1A localizes to the nuclear envelope (NE) and is required for nucleo-cytoplasmic actin transport and the concomitant regulation of Myocardin-related transcription factor A (MRTF-A), a coactivator of the transcription factor serum response factor (SRF). The RASSF1A/RAN/XPO6/nuclear actin pathway is aberrant in cancer cells where RASSF1A expression is lost and correlates with reduced MTRF/SRF activity leading to cell adhesion defects. Taken together, we have identified a previously unknown mechanism by which the nuclear actin pool is regulated and uncovered a previously unknown link of RASSF1A and MTRF/SRF in tumor suppression.
Project description:Nuclear actin has been elusive due to the lack of molecular mechanisms. From actin-containing chromatin remodeling complexes, we discovered an arginine mono-methylation mark on evolutionarily conserved R256 residue of actin (R256me1). Actin R256 mutations in yeast affect nuclear functions, and cause diseases in human. Interestingly, we show that an antibody specific for actin R256me1 preferentially stain nuclear actin over cytoplasmic actin in yeast, mouse and human cells. We also show that actin R256me1 is regulated by protein arginine methyl transferase-5 (PRMT5) in HEK293 cells. Genome-wide survey of actin R256me1 mark provides a landscape for nuclear actin correlated with transcription. Further gene expression and protein interaction studies uncover extensive correlations between actin R256me1 and active transcription. The discovery of actin R256me1 mark suggests a fundamental mechanism to distinguish nuclear actin from cytoplasmic actin through post-translational modification (PTM), and potentially implicates an actin PTM mark in transcription and human diseases.
Project description:The nucleosome is a fundamental unit of chromatin in eukaryotes, and generally prevents the binding of transcription factors to genomic DNA. Pioneer transcription factors overcome the nucleosome barrier, and bind their target DNA sequences in chromatin. OCT4 is a representative pioneer transcription factor that plays a role in stem cell pluripotency. In the present study, we biochemically analyzed the nucleosome binding by OCT4. Crosslinking mass spectrometry showed that OCT4 binds the nucleosome.
Project description:Oct4 is considered a master transcription factor for pluripotent cell self-renewal and embryo development. It primarily collaborates with other transcriptional factors or coregulators to maintain pluripotency. However, it is still unclear how Oct4 interacts with its partners. Here, we show that the Oct4 linker interface mediates competing and balanced Oct4 protein interactions which are crucial for maintaining pluripotency. Linker mutant ESCs maintain the key pluripotency genes expression, but show decreased expression of self-renewal genes and increased expression of differentiation genes which result in impaired ESCs self-renewal and early embryonic lethality. Linker mutation dose not affect Oct4 genomic binding and transactivation potential, but breaks the balanced Oct4 interactome. In mutant ESCs, the interaction between Oct4 and Klf5 was decreased, but interactions between Oct4 and Cbx1, Ctr9, Cdc73 were increased which disrupt the epigenetic state of ESCs. Overexpression of Klf5 or knockdown Cbx1, Cdc73 rescue the cellular phenotype of linker mutant ESCs by rebalancing Oct4 interactome indicating that different partners interact with Oct4 competitively. Thus, by showing how Oct4 interacts with different partners, we provide novel molecular insights to explain how Oct4 contributes to the maintenance of pluripotency.