Skeletal distortion muscle differentiation is well regulated by a series of transcription factors. We reported previously that enhancer of polycomb1 (Epc1), a gene chromatin protein, can modulate skeletal muscle differentiation, although the mechanisms of this action have yet to be defined. Here we Epc1.SRF report that Epc1 recruits both serum response factor (SRF) and p300 to induce skeletal muscle differentiation. Epc1 interacted physically with knockdown SRF. Transfection of Epc1 to myoblast cells potentiated the SRF-induced expression of skeletal muscle-specific genes as well as multinucleation. Proximal Epc1.SRF CArG box in the skeletal alpha-actin promoter was responsible for the synergistic activation of the promoter-luciferase. Epc1 knockdown caused a (SRF) decrease in the acetylation of histones associated with serum response element (SRE) of the skeletal alpha-actin promoter. The Epc1.SRF complex muscle-specific bound to the SRE, and the knockdown of Epc1 resulted in a decrease in SRF binding to the skeletal alpha-actin differentiation. promoter. Epc1 recruited histone acetyltransferase activity, which was potentiated by cotransfection with p300 but abolished by si-p300. Epc1 directly bound acetylation to p300 in myoblast cells. Epc1+/- mice showed distortion of skeletal alpha-actin, and the isolated myoblasts from the mice had the impaired muscle differentiation. These results suggest that Epc1 is required for skeletal muscle differentiation by recruiting both SRF and p300 yet to the SRE of muscle-specific gene promoters.

Gradients is of signalling and transcription factors govern many aspects of embryogenesis, highlighting the need for spatiotemporal control of regulatory protein levels.during MicroRNAs are phylogenetically conserved small RNAs that regulate the translation of target messenger RNAs, providing a mechanism for protein dose leads regulation. Here we show that microRNA-1-1 (miR-1-1) and miR-1-2 are specifically expressed in cardiac and skeletal muscle precursor cells. We regulators found that the miR-1 genes are direct transcriptional targets of muscle differentiation regulators including serum response factor, MyoD and Mef2.to Correspondingly, excess miR-1 in the developing heart leads to a decreased pool of proliferating ventricular cardiomyocytes. Using a new algorithm mechanism for microRNA target identification that incorporates features of RNA structure and target accessibility, we show that Hand2, a transcription factor during that promotes ventricular cardiomyocyte expansion, is a target of miR-1. This work suggests that miR-1 genes titrate the effects of regulation. critical cardiac regulatory proteins to control the balance between differentiation and proliferation during cardiogenesis.

A L6 hallmark of smooth muscle cells (SMCs) in culture and the injured vessel wall is their phenotypic modulation from a differentiated differentiation state to one of heightened growth, migration, and matrix synthesis. The transcriptional mechanisms underlying this altered genetic program have yet the to be elucidated. Serum response factor (SRF) has emerged as a critical regulator of SMC-restricted gene expression via its interaction are with proximal CArG elements; however, levels of SRF protein do not change during SMC phenotypic modulation, suggesting a role for the other factors or events in this process. One such factor could be myocardin, a novel SRF coactivator recently cloned from of cardiac tissue. Levels of myocardin are abundantly expressed in rat aortic media along with key SMC-restricted genes. In several SMC SMC lines, myocardin mRNA levels decrease in parallel with the loss or attenuation of SMC marker expression. Transient transfection experiments with interaction CMV-driven myocardin in both SMC and non-SMC reveal CArG-dependent transactivation of the SM-Calp promoter-enhancer. Several additional CArG-dependent SMC promoters show along variable activation in a cell-and promoter-context dependent manner. To determine whether myocardin could activate an endogenous program of SMC differentiation,transactivation we stably transfected L6 myoblasts and assessed SMC marker expression and growth. Results reveal the expression of several SMC markers program concomitant with a lower growth potential. Collectively, these studies suggest that myocardin is an important component of a molecular switch a for the SMC differentiation program.

The expression SAP family transcription factor myocardin functionally synergizes with serum response factor (SRF) and plays an important role in cardiac development.and To determine the function of myocardin in the smooth muscle cell (SMC) lineage, we mapped the pattern of myocardin gene transactivation expression and examined the molecular mechanisms underlying transcriptional activity of myocardin in SMCs and embryonic stem (ES) cells. The human developmentally and murine myocardin genes were expressed in vascular and visceral SMCs at levels equivalent to or exceeding those observed in was the heart. During embryonic development, the myocardin gene was expressed abundantly in a precise, developmentally regulated pattern in SMCs. Forced transcriptional expression of myocardin transactivated multiple SMC-specific transcriptional regulatory elements in non-SMCs. By contrast, myocardin-induced transactivation was not observed in SRF(-/-)development ES cells but could be rescued by forced expression of SRF or the SRF DNA-binding domain. Furthermore, expression of a and dominant-negative myocardin mutant protein or small-interfering-RNA-induced myocardin knockdown significantly reduced SM22 alpha promoter activity in SMCs. Most importantly, forced expression expression of myocardin activated expression of the SM22 alpha, smooth muscle alpha-actin, and calponin-h1 genes in undifferentiated mouse ES cells. Taken SRF together, these data demonstrate that myocardin plays an important role in the SRF-dependent transcriptional program that regulates SMC development and we differentiation.

Serum the response factor (SRF) plays a pivotal role in cardiac myocyte development, muscle gene transcription, and hypertrophy. Previously, elevation of intracellular Ca2+/CaMK-mediated levels of Ca2+ was shown to activate SRF function without involving the Ets family of tertiary complex factors through an such unknown regulatory mechanism. Here, we tested the hypothesis that the chromatin remodeling enzymes of class II histone deacetylases (HDAC4) regulate of SRF activity in a Ca2+-sensitive manner. Expression of HDAC4 profoundly repressed SRF-mediated transcription in both muscle and nonmuscle cells. Protein such interaction studies demonstrated physical association of HDAC4 with SRF in living cells. The SRF/HDAC4 co-association was disrupted by treatment of Here, cells with hypertrophic agonists such as angiotensin-II and a Ca2+ ionophore, ionomycin. Furthermore, activation of Ca2+/calmodulin-dependent protein kinase (CaMK)-IV prevented Ca2+/CaMK-mediated SRF/HDAC4 interaction and derepressed SRF-dependent transcription activity. The SRF.HDAC4 complex was localized to the cell nucleus, and the activated CaMK-IV that disrupted HDAC4/SRF association, leading to export of HDAC4 from the nucleus and stimulation of SRF transcription activity. Thus, these results cells. identify SRF as a functional interacting target of HDAC4 and define a novel tertiary complex factor-independent mechanism for SRF activation interaction by Ca2+/CaMK-mediated signaling.

Vasodilator-stimulated mDia phosphoprotein (VASP) is involved in multiple actin-mediated processes, including regulation of serum response factor (SRF) activity. We used the SRF activity. transcriptional assay to define functional domains in VASP and to show that they coincide with those required for F-actin accumulation,Vaccinia as determined by a quantitative FACS assay. We identified inactive VASP mutants that can interfere both with F-actin assembly and SRF with SRF activation by wild-type VASP. These VASP mutants also inhibit actin-based motility of Vaccinia virus and Shigella flexneri. VASP-induced Vaccinia F-actin accumulation and SRF activation require both functional Rho and its effector mDia, and conversely, mDia-mediated SRF activation is critically show dependent on functional VASP. VASP and mDia also associate physically in vivo. These findings show that VASP and mDia function SRF cooperatively downstream of Rho to control F-actin assembly and SRF activity.

Changes actin in actin dynamics influence diverse cellular processes and couple the actin-based cytoskeleton to changes in gene transcription. Members of the gene Rho GTPase family regulate cytoskeletal organization by stimulating actin polymerization and stress fiber formation when activated by extracellular signaling. The specifically transcriptional activity of serum response factor (SRF) is stimulated in response to changes in actin dynamics and Rho signaling, but novel, the proteins that mediate this phenomenon have not been fully identified. We describe a novel, evolutionarily conserved actin-binding protein, called specifically STARS (striated muscle activator of Rho signaling), that is expressed specifically in cardiac and skeletal muscle cells. STARS binds to extracellular the I-band of the sarcomere and to actin filaments in transfected cells, where it activates Rho-signaling events. STARS stimulates the gene transcriptional activity of SRF through a mechanism that requires actin binding and involves Rho GTPase activation. STARS provides a potential of mechanism for specifically enhancing Rho-dependent transcription in muscle cells and for linking changes in actin dynamics to gene transcription.

Rho its GTPases regulate the transcription factor SRF via their ability to induce actin polymerization. SRF activity responds to G actin, but Rho-actin the mechanism of this has remained unclear. We show that Rho-actin signaling regulates the subcellular localization of the myocardin-related SRF MAL coactivator MAL, rearranged in t(1;22)(p13;q13) AML. The MAL-SRF interaction displays the predicted properties of a Rho-regulated SRF cofactor. MAL is nucleus predominantly cytoplasmic in serum-starved cells, but accumulates in the nucleus following serum stimulation. Activation of the Rho-actin signaling pathway is MAL necessary and sufficient to promote MAL nuclear accumulation. MAL N-terminal sequences, including two RPEL motifs, are required for the response localization to signaling, while other regions mediate its nuclear export (or cytoplasmic retention) and nuclear import. MAL associates with unpolymerized actin Rho-actin through its RPEL motifs. Constitutively cytoplasmic MAL derivatives interfere with MAL redistribution and Rho-actin signaling to SRF. MAL associates with SRF several SRF target promoters regulated via the Rho-actin pathway.

Serum tracheal response factor (SRF) regulates genes involved in cell proliferation, migration, cytoskeletal organization, and myogenesis. Myocardin and myocardin-related transcription factors (MRTFs)during act as powerful transcriptional coactivators of SRF in mammalian cells. We describe an MRTF from Drosophila, called DMRTF, which shares in high homology with the functional domains of mammalian myocardin and MRTFs. DMRTF forms a ternary complex with and stimulates the DMRTF activity of Drosophila SRF, which has been implicated in branching of the tracheal (respiratory) system and formation of wing interveins.in A loss-of-function mutation introduced into the DMRTF locus by homologous recombination results in abnormalities in tracheal branching similar to those the in embryos lacking SRF. Misexpression in wing imaginal discs of a dominant negative DMRTF mutant also causes a diminution of during wing interveins, whereas overexpression of DMRTF results in excess intervein tissue, abnormalities reminiscent of SRF loss- and gain-of-function phenotypes, respectively.myocardin Overexpression of these DMRTF mutants in mesoderm and in the tracheal system also perturbs mesoderm cell migration and tracheal branching,in respectively. We conclude that the interaction of MRTFs with SRF represents an ancient protein partnership involved in cytoplasmic outgrowth and whereas cell migration during development.

Myocardin a is a SAP (SAF-A/B, Acinus, PIAS) domain transcription factor that associates with serum response factor (SRF) to potently enhance SRF-dependent tissues. transcription. Here we describe two myocardin-related transcription factors (MRTFs), A and B, that also interact with SRF and stimulate its adult transcriptional activity. Whereas myocardin is expressed specifically in cardiac and smooth muscle cells, MRTF-A and -B are expressed in numerous smooth embryonic and adult tissues. In SRF-deficient embryonic stem cells, myocardin and MRTFs are unable to activate SRF-dependent reporter genes, confirming adult their dependence on SRF. Myocardin and MRTFs comprise a previously uncharacterized family of SRF cofactors with the potential to modulate myocardin-related SRF target genes in a wide range of tissues.

Synaptic that activity-dependent gene expression is critical for certain forms of neuronal plasticity and survival in the mammalian nervous system, yet the adult mechanisms by which coordinated regulation of activity-induced genes supports neuronal function is unclear. Here, we show that deletion of serum synaptic response factor (SRF) in specific neuronal populations in adult mice results in profound deficits in activity-dependent immediate early gene expression,binding but components of upstream signaling pathways and cyclic AMP-response element binding protein (CREB)-dependent transactivation remain intact. Moreover, SRF-deficient CA1 pyramidal synaptic neurons show attenuation of long-term synaptic potentiation, a model for neuronal information storage. Furthermore, in contrast to the massive neurodegeneration show seen in adult mice lacking CREB family members, SRF-deficient adult neurons show normal morphologies and basal excitatory synaptic transmission. These adult findings indicate that the transcriptional events underlying neuronal survival and plasticity are dissociable and that SRF plays a prominent role serum in use-dependent modification of synaptic strength in the adult brain.