Physiological Control of Smooth Muscle-specific Gene Expression through Regulated Nuclear Translocation of Serum Response Factor

Serum response factor (SRF) is a key transcriptional activator of the c-fos gene and of muscle-specific gene expression. We have identified four forms of the SRF coding sequence, SRF-L (the previously identified form), SRF-M, SRF-S and SRF-I, that are produced by alternative splicing. The new forms of SRF lack regions of the C-terminal transactivation domain by splicing out of exon 5 (SRF-M), exons 4 and 5 (SRF-S) and exons 3, 4 and 5 (SRF-I). SRF-M is expressed at similar levels to SRF-L in differentiated vascular smooth-muscle cells and skeletal-muscle cells, whereas SRF-L is the predominant form in many other tissues. SRF-S expression is restricted to vascular smooth muscle and SRF-I expression is restricted to the embryo. Transfection of SRF-L and SRF-M into C2C12 cells showed that both forms are transactivators of the promoter of the smooth-muscle-specific gene SM22α, whereas SRF-I acted as a dominant negative form of SRF.

Download Full-text

New Role for Serum Response Factor in Postnatal Skeletal Muscle Growth and Regeneration via the Interleukin 4 and Insulin-Like Growth Factor 1 Pathways

Molecular and Cellular Biology ◽

10.1128/mcb.00138-06 ◽

2006 ◽

Vol 26 (17) ◽

pp. 6664-6674 ◽

Cited By ~ 53

Author(s):

Claude Charvet ◽

Christophe Houbron ◽

Ara Parlakian ◽

Julien Giordani ◽

Charlotte Lahoute ◽

...

Keyword(s):

Gene Expression ◽

Skeletal Muscle ◽

Growth Factor ◽

Serum Response Factor ◽

Muscle Growth ◽

Interleukin 4 ◽

Specific Gene ◽

Response Factor ◽

Insulin Like Growth Factor ◽

Serum Response

ABSTRACT Serum response factor (SRF) is a crucial transcriptional factor for muscle-specific gene expression. We investigated SRF function in adult skeletal muscles, using mice with a postmitotic myofiber-targeted disruption of the SRF gene. Mutant mice displayed severe skeletal muscle mass reductions due to a postnatal muscle growth defect resulting in highly hypotrophic adult myofibers. SRF-depleted myofibers also failed to regenerate following injury. Muscles lacking SRF had very low levels of muscle creatine kinase and skeletal alpha-actin (SKA) transcripts and displayed other alterations to the gene expression program, indicating an overall immaturity of mutant muscles. This loss of SKA expression, together with a decrease in beta-tropomyosin expression, contributed to myofiber growth defects, as suggested by the extensive sarcomere disorganization found in mutant muscles. However, we observed a downregulation of interleukin 4 (IL-4) and insulin-like growth factor 1 (IGF-1) expression in mutant myofibers which could also account for their defective growth and regeneration. Indeed, our demonstration of SRF binding to interleukin 4 and IGF-1 promoters in vivo suggests a new crucial role for SRF in pathways involved in muscle growth and regeneration.

Download Full-text

The single-strand DNA/RNA-binding protein, Purβ, regulates serum response factor (SRF)-mediated cardiac muscle gene expressionThis paper is one of a selection of papers published in this Special Issue, entitled The Cellular and Molecular Basis of Cardiovascular Dysfunction, Dhalla 70th Birthday Tribute.

Canadian Journal of Physiology and Pharmacology ◽

10.1139/y07-009 ◽

2007 ◽

Vol 85 (3-4) ◽

pp. 349-359 ◽

Cited By ~ 7

Author(s):

Madhu Gupta ◽

Vithida Sueblinvong ◽

Mahesh P. Gupta

Keyword(s):

Gene Expression ◽

Cardiac Muscle ◽

Rna Binding ◽

Serum Response Factor ◽

Single Strand ◽

Specific Gene ◽

Response Factor ◽

Repressive Effect ◽

Muscle Gene ◽

Serum Response

Single-strand DNA-binding proteins, Purα and Purβ, play a role in cell growth and differentiation by modulating both transcriptional and translational controls of gene expression. We have previously characterized binding of Purα and Purβ proteins to a purine-rich negative regulatory (PNR) element of the rat cardiac α-myosin heavy chain (MHC) gene that controls cardiac muscle specificity. In this study we investigated the role of upstream sequences of the α-MHC promoter in Purβ-mediated gene repression. In the transient transfection analysis overexpression of Purβ revealed a negative regulatory effect on serum response factor (SRF)-dependent α-MHC and α-skeletal actin expression in muscle cell background. Contrary, in nonmuscle cells, Purβ showed no repressive effect. The results obtained from gel-shift assays demonstrated a sequence specific competitive binding of Purβ to the minus strand of the SRF-binding, CArG box sequences of different muscle genes, but not to the SRF-binding, SRE sequences of the c-fos gene. These element-specific associations of Purβ with muscle CArG boxes may, in part, explain why muscle gene expression is downregulated in disease states in which Purβ levels are elevated. This data also provide a mechanistic distinction between muscle CArG boxes and nonmuscle serum response element (SRE) sequences in terms of their affinity to bind to SRF and their ability to regulate cell-specific gene expression.

Download Full-text

A serum response factor-dependent transcriptional regulatory program identifies distinct smooth muscle cell sublineages.

Molecular and Cellular Biology ◽

10.1128/mcb.17.4.2266 ◽

1997 ◽

Vol 17 (4) ◽

pp. 2266-2278 ◽

Cited By ~ 169

Author(s):

S Kim ◽

H S Ip ◽

M M Lu ◽

C Clendenin ◽

M S Parmacek

Keyword(s):

Gene Expression ◽

Smooth Muscle ◽

Transgenic Mice ◽

Smooth Muscle Cell ◽

Muscle Cell ◽

Promoter Activity ◽

Serum Response Factor ◽

Response Factor ◽

Transcriptional Regulatory ◽

Serum Response

The SM22alpha promoter has been used as a model system to define the molecular mechanisms that regulate smooth muscle cell (SMC) specific gene expression during mammalian development. The SM22alpha gene is expressed exclusively in vascular and visceral SMCs during postnatal development and is transiently expressed in the heart and somites during embryogenesis. Analysis of the SM22alpha promoter in transgenic mice revealed that 280 bp of 5' flanking sequence is sufficient to restrict expression of the lacZ reporter gene to arterial SMCs and the myotomal component of the somites. DNase I footprint and electrophoretic mobility shift analyses revealed that the SM22alpha promoter contains six nuclear protein binding sites (designated smooth muscle elements [SMEs] -1 to -6, respectively), two of which bind serum response factor (SRF) (SME-1 and SME-4). Mutational analyses demonstrated that a two-nucleotide substitution that selectively eliminates SRF binding to SME-4 decreases SM22alpha promoter activity in arterial SMCs by approximately 90%. Moreover, mutations that abolish binding of SRF to SME-1 and SME-4 or mutations that eliminate each SME-3 binding activity totally abolished SM22alpha promoter activity in the arterial SMCs and somites of transgenic mice. Finally, we have shown that a multimerized copy of SME-4 (bp -190 to -110) when linked to the minimal SM22alpha promoter (bp -90 to +41) is necessary and sufficient to direct high-level transcription in an SMC lineage-restricted fashion. Taken together, these data demonstrate that distinct transcriptional regulatory programs control SM22alpha gene expression in arterial versus visceral SMCs. Moreover, these data are consistent with a model in which combinatorial interactions between SRF and other transcription factors that bind to SME-4 (and that bind directly to SRF) activate transcription of the SM22alpha gene in arterial SMCs.

Download Full-text

Serum response factor neutralizes Purα- and Purβ-mediated repression of the fetal vascular smooth muscle α-actin gene in stressed adult cardiomyocytes

AJP Cell Physiology ◽

10.1152/ajpcell.00173.2007 ◽

2008 ◽

Vol 294 (3) ◽

pp. C702-C714 ◽

Cited By ~ 11

Author(s):

Aiwen Zhang ◽

Jason J. David ◽

Sukanya V. Subramanian ◽

Xiaoying Liu ◽

Matthew D. Fuerst ◽

...

Keyword(s):

Gene Expression ◽

Smooth Muscle ◽

Gene Transcription ◽

Serum Response Factor ◽

De Novo ◽

Ischemia Reperfusion Injury ◽

Ischemia Reperfusion ◽

Response Factor ◽

Adult Cardiomyocytes ◽

Serum Response

Mouse hearts subjected to repeated transplant surgery and ischemia-reperfusion injury develop substantial interstitial and perivascular fibrosis that was spatially associated with dysfunctional activation of fetal smooth muscle α-actin (SMαA) gene expression in graft ventricular cardiomyocytes. Compared with cardiac fibroblasts in which nuclear levels of the Sp1 and Smad 2/3 transcriptional-activating proteins increased markedly after transplant injury, the most abundant SMαA gene-activating protein in cardiomyocyte nuclei was serum response factor (SRF). Additionally, cardiac intercalated discs in heart grafts contained substantial deposits of Purα, an mRNA-binding protein and known negative modulator of SRF-activated SMαA gene transcription. Activation of fetal SMαA gene expression in perfusion-isolated adult cardiomyocytes was linked to elevated binding of a novel protein complex consisting of SRF and Purα to a purine-rich DNA element in the SMαA promoter called SPUR, previously shown to be required for induction of SMαA gene transcription in injury-activated myofibroblasts. Increased SRF binding to SPUR DNA plus one of two nearby CArG box consensus elements was observed in SMαA-positive cardiomyocytes in parallel with enhanced Purα:SPUR protein:protein interaction. The data suggest that de novo activation of the normally silent SMαA gene in reprogrammed adult cardiomyocytes is linked to elevated interaction of SRF with fetal-specific CArG and injury-activated SPUR elements in the SMαA promoter as well as the appearance of novel Purα protein complexes in both the nuclear and cytosolic compartments of these cells.

Download Full-text