Interaction of Serum Response Factor (SRF) with the Elk-1 B Box Inhibits RhoA-Actin Signaling to SRF and Potentiates Transcriptional Activation by Elk-1

ABSTRACT Serum response factor (SRF) is a transcription factor which regulates many immediate-early genes. Rho GTPases regulate SRF activity through changes in actin dynamics, but some SRF target genes, such as c-fos, are insensitive to this pathway. At the c-fos promoter, SRF recruits members of the ternary complex factor (TCF) family of Ets domain proteins through interactions with the TCF B-box region. Analysis of c-fos promoter mutations demonstrates that the TCF and ATF/AP1 sites adjoining the SRF binding site inhibit activation of the promoter by RhoA-actin signaling. The presence of the TCF binding site is sufficient for inhibition, and experiments with an altered-specificity Elk-1 derivative demonstrate that inhibition can be mediated by the Elk-1 TCF. Using Elk-1 fusion proteins that can bind DNA autonomously, we show that inhibition of RhoA-actin signaling requires physical interaction between the Elk-1 B box and SRF. These results account for the insensitivity of c-fos to RhoA-actin signaling. Interaction of the B box with SRF also potentiates transcriptional activation by the Elk-1 C-terminal activation domain. Combinatorial interactions between SRF and TCF proteins are thus likely to play an important role in determining the relative sensitivity of SRF target genes to Ras- and Rho-controlled signal transduction pathways.

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Serum response factor: master regulator of the actin cytoskeleton and contractile apparatus

AJP Cell Physiology ◽

10.1152/ajpcell.00386.2006 ◽

2007 ◽

Vol 292 (1) ◽

pp. C70-C81 ◽

Cited By ~ 298

Author(s):

Joseph M. Miano ◽

Xiaochun Long ◽

Keigi Fujiwara

Keyword(s):

Transcription Factor ◽

Actin Cytoskeleton ◽

Target Genes ◽

Serum Response Factor ◽

Cellular Growth ◽

Cellular Migration ◽

Actin Dynamics ◽

Response Factor ◽

Master Regulator ◽

Serum Response

Serum response factor (SRF) is a highly conserved and widely expressed, single copy transcription factor that theoretically binds up to 1,216 permutations of a 10-base pair cis element known as the CArG box. SRF-binding sites were defined initially in growth-related genes. Gene inactivation or knockdown studies in species ranging from unicellular eukaryotes to mice have consistently shown loss of SRF to be incompatible with life. However, rather than being critical for proliferation and growth, these genetic studies point to a crucial role for SRF in cellular migration and normal actin cytoskeleton and contractile biology. In fact, recent genomic studies reveal nearly half of the >200 SRF target genes encoding proteins with functions related to actin dynamics, lamellipodial/filopodial formation, integrin-cytoskeletal coupling, myofibrillogenesis, and muscle contraction. SRF has therefore emerged as a dispensable transcription factor for cellular growth but an absolutely essential orchestrator of actin cytoskeleton and contractile homeostasis. This review summarizes the recent genomic and genetic analyses of CArG-SRF that support its role as an ancient, master regulator of the actin cytoskeleton and contractile machinery.

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Mutant Actins Demonstrate a Role for Unpolymerized Actin in Control of Transcription by Serum Response Factor

Molecular Biology of the Cell ◽

10.1091/mbc.02-05-0068 ◽

2002 ◽

Vol 13 (12) ◽

pp. 4167-4178 ◽

Cited By ~ 164

Author(s):

Guido Posern ◽

Athanassia Sotiropoulos ◽

Richard Treisman

Keyword(s):

Nuclear Export ◽

Serum Response Factor ◽

Ectopic Expression ◽

Actin Dynamics ◽

Physical Interaction ◽

Response Factor ◽

Cell Fractionation ◽

Direct Role ◽

Serum Response ◽

Two Hybrid

Signal-induced activation of the transcription factor serum response factor (SRF) requires alterations in actin dynamics. SRF activity can be inhibited by ectopic expression of β-actin, either because actin itself participates in SRF regulation or as a consequence of cytoskeletal perturbations. To distinguish between these possibilities, we studied actin mutants. Three mutant actins, G13R, R62D, and a C-terminal VP16 fusion protein, were shown not to polymerize in vivo, as judged by two-hybrid, immunofluorescence, and cell fractionation studies. These actins effectively inhibited SRF activation, as did wild-type actin, which increased the G-actin level without altering the F:G-actin ratio. Physical interaction between SRF and actin was not detectable by mammalian or yeast two-hybrid assays, suggesting that SRF regulation involves an unidentified cofactor. SRF activity was not blocked upon inhibition of CRM1-mediated nuclear export by leptomycin B. Two actin mutants were identified, V159N and S14C, whose expression favored F-actin formation and which strongly activated SRF in the absence of external signals. These mutants seemed unable to inhibit SRF activity, because their expression did not reduce the absolute level of G-actin as assessed by DNase I binding. Taken together, these results provide strong evidence that G-actin, or a subpopulation of it, plays a direct role in signal transduction to SRF.

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Target Gene-Specific Modulation of Myocardin Activity by GATA Transcription Factors

Molecular and Cellular Biology ◽

10.1128/mcb.24.19.8519-8528.2004 ◽

2004 ◽

Vol 24 (19) ◽

pp. 8519-8528 ◽

Cited By ~ 44

Author(s):

Jiyeon Oh ◽

Zhigao Wang ◽

Da-Zhi Wang ◽

Ching-Ling Lien ◽

Weibing Xing ◽

...

Keyword(s):

Transcription Factors ◽

Target Gene ◽

Target Genes ◽

Serum Response Factor ◽

Fine Tuning ◽

Physical Interaction ◽

Response Factor ◽

Muscle Gene Expression ◽

Gata Transcription Factors ◽

Serum Response

ABSTRACT Myocardin is a transcriptional coactivator that regulates cardiac and smooth muscle gene expression by associating with serum response factor. We show that GATA transcription factors can either stimulate or suppress the transcriptional activity of myocardin, depending on the target gene. Modulation of myocardin activity by GATA4 is mediated by the physical interaction of myocardin with the DNA binding domain of GATA4 but does not require binding of GATA4 to DNA. Paradoxically, the transcription activation domain of GATA4 is dispensable for the stimulatory effect of GATA4 on myocardin activity but is required for repression of myocardin activity. The ability of GATA transcription factors to modulate myocardin activity provides a potential mechanism for fine tuning the expression of serum response factor target genes in a gene-specific manner.

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Casein kinase II phosphorylation increases the rate of serum response factor-binding site exchange.

The EMBO Journal ◽

10.1002/j.1460-2075.1992.tb05032.x ◽

1992 ◽

Vol 11 (1) ◽

pp. 97-105 ◽

Cited By ~ 97

Author(s):

R.M. Marais ◽

J.J. Hsuan ◽

C. McGuigan ◽

J. Wynne ◽

R. Treisman

Keyword(s):

Binding Site ◽

Serum Response Factor ◽

Casein Kinase Ii ◽

Casein Kinase ◽

Response Factor ◽

Factor Binding Site ◽

Factor Binding ◽

Site Exchange ◽

Serum Response

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Serum Response Factor (SRF)-cofilin-actin signaling axis modulates mitochondrial dynamics

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1208141109 ◽

2012 ◽

Vol 109 (38) ◽

pp. E2523-E2532 ◽

Cited By ~ 29

Author(s):

Henning Beck ◽

Kevin Flynn ◽

Katrin S. Lindenberg ◽

Heinz Schwarz ◽

Frank Bradke ◽

...

Keyword(s):

Mitochondrial Function ◽

Serum Response Factor ◽

Mitochondrial Dynamics ◽

Actin Dynamics ◽

Response Factor ◽

Signaling Axis ◽

Mitochondrial Number ◽

Mitochondrial Networks ◽

The Impact ◽

Serum Response

Aberrant mitochondrial function, morphology, and transport are main features of neurodegenerative diseases. To date, mitochondrial transport within neurons is thought to rely mainly on microtubules, whereas actin might mediate short-range movements and mitochondrial anchoring. Here, we analyzed the impact of actin on neuronal mitochondrial size and localization. F-actin enhanced mitochondrial size and mitochondrial number in neurites and growth cones. In contrast, raising G-actin resulted in mitochondrial fragmentation and decreased mitochondrial abundance. Cellular F-actin/G-actin levels also regulate serum response factor (SRF)-mediated gene regulation, suggesting a possible link between SRF and mitochondrial dynamics. Indeed, SRF-deficient neurons display neurodegenerative hallmarks of mitochondria, including disrupted morphology, fragmentation, and impaired mitochondrial motility, as well as ATP energy metabolism. Conversely, constitutively active SRF-VP16 induced formation of mitochondrial networks and rescued huntingtin (HTT)-impaired mitochondrial dynamics. Finally, SRF and actin dynamics are connected via the actin severing protein cofilin and its slingshot phosphatase to modulate neuronal mitochondrial dynamics. In summary, our data suggest that the SRF-cofilin-actin signaling axis modulates neuronal mitochondrial function.

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The Cytoskeleton-associated PDZ-LIM Protein, ALP, Acts on Serum Response Factor Activity to Regulate Muscle Differentiation

Molecular Biology of the Cell ◽

10.1091/mbc.e06-09-0815 ◽

2007 ◽

Vol 18 (5) ◽

pp. 1723-1733 ◽

Cited By ~ 19

Author(s):

Pascal Pomiès ◽

Mohammad Pashmforoush ◽

Cristina Vegezzi ◽

Kenneth R. Chien ◽

Charles Auffray ◽

...

Keyword(s):

Serum Response Factor ◽

Critical Role ◽

Muscle Differentiation ◽

Actin Dynamics ◽

Response Factor ◽

Cytoskeletal Regulation ◽

Expression Construct ◽

Filament Bundles ◽

Serum Response

In this report, an antisense RNA strategy has allowed us to show that disruption of ALP expression affects the expression of the muscle transcription factors myogenin and MyoD, resulting in the inhibition of muscle differentiation. Introduction of a MyoD expression construct into ALP-antisense cells is sufficient to restore the capacity of the cells to differentiate, illustrating that ALP function occurs upstream of MyoD. It is known that MyoD is under the control of serum response factor (SRF), a transcriptional regulator whose activity is modulated by actin dynamics. A dramatic reduction of actin filament bundles is observed in ALP-antisense cells and treatment of these cells with the actin-stabilizing drug jasplakinolide stimulates SRF activity and restores the capacity of the cells to differentiate. Furthermore, we show that modulation of ALP expression influences SRF activity, the level of its coactivator, MAL, and muscle differentiation. Collectively, these results suggest a critical role of ALP on muscle differentiation, likely via cytoskeletal regulation of SRF.

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RAGE‐DIAPH1 modulates hyperglycemia driven induction of Serum response factor target genes in cardiac cells

The FASEB Journal ◽

10.1096/fasebj.2019.33.1_supplement.830.9 ◽

2019 ◽

Vol 33 (S1) ◽

Author(s):

Gopalkrishna Sreejit ◽

Nosirudeen Quadri ◽

Radha Ananthakrishnan ◽

Ann Marie Schmidt ◽

Ravichandran Ramasamy

Keyword(s):

Target Genes ◽

Serum Response Factor ◽

Cardiac Cells ◽

Response Factor ◽

Serum Response

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Maximal serum stimulation of the c-fos serum response element requires both the serum response factor and a novel binding factor, SRE-binding protein

Molecular and Cellular Biology ◽

10.1128/mcb.12.10.4769-4783.1992 ◽

1992 ◽

Vol 12 (10) ◽

pp. 4769-4783

Author(s):

A M Boulden ◽

L J Sealy

Keyword(s):

Long Terminal Repeat ◽

Binding Site ◽

Rous Sarcoma Virus ◽

Serum Response Factor ◽

Response Factor ◽

High Affinity ◽

Rous Sarcoma ◽

Binding Factor ◽

Sarcoma Virus ◽

Serum Response

We have previously reported on the presence of a CArG motif at -100 in the Rous sarcoma virus long terminal repeat which binds an avian nuclear protein termed enhancer factor III (EFIII) (A. Boulden and L. Sealy, Virology 174:204-216, 1990). By all analyses, EFIII protein appears to be the avian homolog of the serum response factor (SRF). In this study, we identify a second CArG motif (EFIIIB) in the Rous sarcoma virus long terminal repeat enhancer at -162 and show only slightly lower binding affinity of the EFIII/SRF protein for this element in comparison with c-fos serum response element (SRE) and EFIII DNAs. Although all three elements bind the SRF with similar affinities, serum induction mediated by the c-fos SRE greatly exceeds that effected by the EFIII or EFIIIB sequence. We postulated that this difference in serum inducibility might result from binding of factors other than the SRF which occurs on the c-fos SRE but not on EFIII and EFIIIB sequences. Upon closer inspection of nuclear proteins which bind the c-fos SRE in chicken embryo fibroblast and NIH 3T3 nuclear extracts, we discovered another binding factor, SRE-binding protein (SRE BP), which fails to recognize EFIII DNA with high affinity. Competition analyses, methylation interference, and site-directed mutagenesis have determined that the SRE BP binding element overlaps and lies immediately 3' to the CArG box of the c-fos SRE. Mutation of the c-fos SRE so that it no longer binds SRE BP reduces serum inducibility to 33% of the wild-type level. Conversely, mutation of the EFIII sequence so that it binds SRE BP with high affinity results in a 400% increase in serum induction, with maximal stimulation equaling that of the c-fos SRE. We conclude that binding of both SRE BP and SRF is required for maximal serum induction. The SRE BP binding site coincides with the recently reported binding site for rNF-IL6 on the c-fos SRE. Nonetheless, we show that SRE BP is distinct from rNF-IL6, and identification of this novel factor is being pursued.

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