scholarly journals A novel function of the monomeric CCTε subunit connects the serum response factor pathway to chaperone-mediated actin folding

2015 ◽  
Vol 26 (15) ◽  
pp. 2801-2809 ◽  
Author(s):  
Kerryn L. Elliott ◽  
Andreas Svanström ◽  
Matthias Spiess ◽  
Roger Karlsson ◽  
Julie Grantham
Keyword(s):  
Mammalian Cells ◽  
Actin Polymerization ◽  
Serum Response Factor ◽  
Actin Binding ◽  
Nuclear Accumulation ◽  
Response Factor ◽  
Actin Assembly ◽  
Actin Expression ◽  
Serum Response ◽  
Substrate Binding Domain

Correct protein folding is fundamental for maintaining protein homeostasis and avoiding the formation of potentially cytotoxic protein aggregates. Although some proteins appear to fold unaided, actin requires assistance from the oligomeric molecular chaperone CCT. Here we report an additional connection between CCT and actin by identifying one of the CCT subunits, CCTε, as a component of the myocardin-related cotranscription factor-A (MRTF-A)/serum response factor (SRF) pathway. The SRF pathway registers changes in G-actin levels, leading to the transcriptional up-regulation of a large number of genes after actin polymerization. These genes encode numerous actin-binding proteins as well as actin. We show that depletion of the CCTε subunit by siRNA enhances SRF signaling in cultured mammalian cells by an actin assembly-independent mechanism. Overexpression of CCTε in its monomeric form revealed that CCTε binds via its substrate-binding domain to the C-terminal region of MRTF-A and that CCTε is able to alter the nuclear accumulation of MRTF-A after stimulation by serum addition. Given that the levels of monomeric CCTε conversely reflect the levels of CCT oligomer, our results suggest that CCTε provides a connection between the actin-folding capacity of the cell and actin expression.

scholarly journals Muscle-Specific Signaling Mechanism That Links Actin Dynamics to Serum Response Factor

2005 ◽  
Vol 25 (8) ◽  
pp. 3173-3181 ◽  
Author(s):  
Koichiro Kuwahara ◽  
Tomasa Barrientos ◽  
G. C. Teg Pipes ◽  
Shijie Li ◽  
Eric N. Olson
Keyword(s):  
Actin Polymerization ◽  
Serum Response Factor ◽  
Striated Muscle ◽  
Nuclear Translocation ◽  
Actin Dynamics ◽  
Actin Binding ◽  
Response Factor ◽  
Signaling Mechanism ◽  
Muscle Gene Expression ◽  
Serum Response

ABSTRACT Myocardin and the myocardin-related transcription factors (MRTFs) MRTF-A and MRTF-B are coactivators for serum response factor (SRF), which regulates genes involved in cell proliferation, migration, cytoskeletal dynamics, and myogenesis. MRTF-A has been shown to translocate to the nucleus and activate SRF in response to Rho signaling and actin polymerization. Previously, we described a muscle-specific actin-binding protein named striated muscle activator of Rho signaling (STARS) that also activates SRF through a Rho-dependent mechanism. Here we show that STARS activates SRF by inducing the nuclear translocation of MRTFs. The STARS-dependent nuclear import of MRTFs requires RhoA and actin polymerization, and the actin-binding domain of STARS is necessary and sufficient for this activity. A knockdown of endogenous STARS expression by using small interfering RNA significantly reduced SRF activity in differentiated C2C12 skeletal muscle cells and cardiac myocytes. The ability of STARS to promote the nuclear localization of MRTFs and SRF-mediated transcription provides a potential muscle-specific mechanism for linking changes in actin dynamics and sarcomere structure with striated muscle gene expression.

scholarly journals The Diaphanous-related Formin mDia1 Controls Serum Response Factor Activity through its Effects on Actin Polymerization

2002 ◽  
Vol 13 (11) ◽  
pp. 4088-4099 ◽  
Author(s):  
John W. Copeland ◽  
Richard Treisman
Keyword(s):  
Actin Polymerization ◽  
Serum Response Factor ◽  
Signal Pathway ◽  
Small Gtpase ◽  
Actin Dynamics ◽  
Actin Assembly ◽  
Extracellular Signals ◽  
Activation Assay ◽  
The Relationship ◽  
Serum Response

SRF-dependent transcription is regulated by the small GTPase RhoA via its effects on actin dynamics. The diaphanous-related formin (DRF) proteins have been identified as candidate RhoA effectors mediating signaling to SRF. Here we investigate the relationship between SRF activation and actin polymerization by the DRF mDia1. We show that the ability of mDia1 to potentiate SRF activity is strictly correlated with its ability to promote F-actin assembly. Both processes can occur independently of the mDia1 FH1 domain but require sequences in an extended C-terminal region encompassing the conserved FH2 domain. mDia-mediated SRF activation, but not F-actin assembly, can be blocked by a nonpolymerizable actin mutant, placing actin downstream of mDia in the signal pathway. The SRF activation assay was used to identify inactive mDia1 derivatives that inhibit serum- and LPA-induced signaling to SRF. We show that these interfering mutants also block F-actin assembly, whether induced by mDia proteins or extracellular signals. These results identify novel functional elements of mDia1 and show that it regulates SRF activity by inducing depletion of the cellular pool of G-actin.

scholarly journals Molecular basis for G-actin binding to RPEL motifs from the serum response factor coactivator MAL

2008 ◽  
Vol 27 (23) ◽  
pp. 3198-3208 ◽  
Author(s):  
Stephane Mouilleron ◽  
Sebastian Guettler ◽  
Carola A Langer ◽  
Richard Treisman ◽  
Neil Q McDonald
Keyword(s):  
Molecular Basis ◽  
Serum Response Factor ◽  
Actin Binding ◽  
Response Factor ◽  
Serum Response

scholarly journals Serum-Induced Phosphorylation of the Serum Response Factor Coactivator MKL1 by the Extracellular Signal-Regulated Kinase 1/2 Pathway Inhibits Its Nuclear Localization

2008 ◽  
Vol 28 (20) ◽  
pp. 6302-6313 ◽  
Author(s):  
Susanne Muehlich ◽  
Ruigong Wang ◽  
Seung-Min Lee ◽  
Thera C. Lewis ◽  
Chao Dai ◽  
...  
Keyword(s):  
Nuclear Localization ◽  
Nuclear Export ◽  
Serum Response Factor ◽  
Phosphorylation Site ◽  
Mitogen Activated Protein Kinase ◽  
Actin Binding ◽  
Response Factor ◽  
Extracellular Signal Regulated Kinase ◽  
Extracellular Signal ◽  
Serum Response

ABSTRACT Megakaryoblastic leukemia 1 (MKL1) is a myocardin-related coactivator of the serum response factor (SRF) transcription factor, which has an integral role in differentiation, migration, and proliferation. Serum induces RhoA-dependent translocation of MKL1 from the cytoplasm to the nucleus and also causes a rapid increase in MKL1 phosphorylation. We have mapped a serum-inducible phosphorylation site and found, surprisingly, that its mutation causes constitutive localization to the nucleus, suggesting that phosphorylation of MKL1 inhibits its serum-induced nuclear localization. The key site, serine 454, resembles a mitogen-activated protein kinase phosphorylation site, and its modification was blocked by the MEK1 inhibitor U0126, implying that extracellular signal-regulated kinase 1/2 (ERK1/2) is the serum-inducible kinase that phosphorylates MKL1. Previous results indicated that G-actin binding to MKL1 promotes its nuclear export, and we found that MKL1 phosphorylation is required for its binding to actin, explaining its effect on localization. We propose a model in which serum induction initially stimulates MKL1 nuclear localization due to a decrease in G-actin levels, but MKL1 is then downregulated by nuclear export due to ERK1/2 phosphorylation.

scholarly journals LIM kinase and Diaphanous cooperate to regulate serum response factor and actin dynamics

2002 ◽  
Vol 157 (5) ◽  
pp. 831-838 ◽  
Author(s):  
Olivier Geneste ◽  
John W. Copeland ◽  
Richard Treisman
Keyword(s):  
Actin Polymerization ◽  
Serum Response Factor ◽  
Rho Kinase ◽  
Small Gtpase ◽  
Actin Dynamics ◽  
Response Factor ◽  
Lim Kinase ◽  
Serum Stimulation ◽  
Effector Pathways ◽  
Serum Response

The small GTPase RhoA controls activity of serum response factor (SRF) by inducing changes in actin dynamics. We show that in PC12 cells, activation of SRF after serum stimulation is RhoA dependent, requiring both actin polymerization and the Rho kinase (ROCK)–LIM kinase (LIMK)–cofilin signaling pathway, previously shown to control F-actin turnover. Activation of SRF by overexpression of wild-type LIMK or ROCK-insensitive LIMK mutants also requires functional RhoA, indicating that a second RhoA-dependent signal is involved. This is provided by the RhoA effector mDia: dominant interfering mDia1 derivatives inhibit both serum- and LIMK-induced SRF activation and reduce the ability of LIMK to induce F-actin accumulation. These results demonstrate a role for LIMK in SRF activation, and functional cooperation between RhoA-controlled LIMK and mDia effector pathways.

scholarly journals RPEL Motifs Link the Serum Response Factor Cofactor MAL but Not Myocardin to Rho Signaling via Actin Binding

2007 ◽  
Vol 28 (2) ◽  
pp. 732-742 ◽  
Author(s):  
Sebastian Guettler ◽  
Maria K. Vartiainen ◽  
Francesc Miralles ◽  
Banafshe Larijani ◽  
Richard Treisman
Keyword(s):  
Transcription Factor ◽  
Family Member ◽  
Serum Response Factor ◽  
Rho Gtpase ◽  
Nucleocytoplasmic Transport ◽  
Actin Binding ◽  
Response Factor ◽  
Nucleocytoplasmic Shuttling ◽  
Related Transcription Factor ◽  
Serum Response

ABSTRACT Myocardin (MC) family proteins are transcriptional coactivators for serum response factor (SRF). Each family member possesses a conserved N-terminal region containing three RPEL motifs (the “RPEL domain”). MAL/MKL1/myocardin-related transcription factor A is cytoplasmic, accumulating in the nucleus upon activation of Rho GTPase signaling, which alters interactions between G-actin and the RPEL domain. We demonstrate that MC, which is nuclear, does not shuttle through the cytoplasm and that the contrasting nucleocytoplasmic shuttling properties of MAL and MC are defined by their RPEL domains. We show that the MAL RPEL domain binds actin more avidly than that of MC and that the RPEL motif itself is an actin-binding element. RPEL1 and RPEL2 of MC bind actin weakly compared with those of MAL, while RPEL3 is of comparable and low affinity in the two proteins. Actin binding by all three motifs is required for MAL regulation. The differing behaviors of MAL and MC are specified by the RPEL1-RPEL2 unit, while RPEL3 can be exchanged between them. We propose that differential actin occupancy of multiple RPEL motifs regulates nucleocytoplasmic transport and activity of MAL.

scholarly journals The nature and intensity of mechanical stimulation drive different dynamics of MRTF-A nuclear redistribution after actin remodeling in myoblasts

2018 ◽  
Author(s):  
Lorraine Montel ◽  
Athanassia Sotiropoulos ◽  
Sylvie Hénon
Keyword(s):  
Mechanical Stimulation ◽  
Actin Polymerization ◽  
Target Genes ◽  
Serum Response Factor ◽  
Magnetic Tweezers ◽  
Point Of View ◽  
Nuclear Accumulation ◽  
Related Transcription Factor ◽  
Global Increase ◽  
Serum Response

AbstractSerum response factor and its cofactor myocardin-related transcription factor (MRTF) are key elements of muscle-mass adaptation to workload. The transcription of target genes is activated when MRTF is present in the nucleus. The localization of MRTF is controlled by its binding to G-actin. Thus, the pathway can be mechanically activated through the mechanosensitivity of the actin cytoskeleton. The pathway has been widely investigated from a biochemical point of view, but its mechanical activation and the timescales involved are poorly understood. Here, we applied local and global mechanical cues to myoblasts through two custom-built set-ups, magnetic tweezers and stretchable substrates. Both induced nuclear accumulation of MRTF-A. However, the dynamics of the response varied with the nature and level of mechanical stimulation and correlated with the polymerization of different actin sub-structures. Local repeated force induced local actin polymerization and nuclear accumulation of MRTF-A by 30 minutes, whereas a global static strain induced both rapid (minutes) transient nuclear accumulation, associated with the polymerization of an actin cap above the nucleus, and long-term (hours) accumulation, with a global increase in polymerized actin. Conversely, high strain induced actin depolymerization at intermediate times, associated with cytoplasmic MRTF accumulation.

scholarly journals The pruned gene encodes the Drosophila serum response factor and regulates cytoplasmic outgrowth during terminal branching of the tracheal system

Development ◽  
1996 ◽  
Vol 122 (5) ◽  
pp. 1353-1362 ◽  
Author(s):  
K. Guillemin ◽  
J. Groppe ◽  
K. Ducker ◽  
R. Treisman ◽  
E. Hafen ◽  
...  
Keyword(s):  
Mammalian Cells ◽  
Ternary Complex ◽  
Serum Response Factor ◽  
Response Factor ◽  
Loss Of Function ◽  
Tracheal System ◽  
Expression Of Genes ◽  
Serum Response ◽  
Cytoplasmic Processes ◽  
Ternary Complex Factor

We identified a Drosophila gene, pruned, that regulates formation of the terminal branches of the tracheal (respiratory) system. These branches arise by extension of long cytoplasmic processes from terminal tracheal cells towards oxygen-starved tissues, followed by formation of a lumen within the processes. The pruned gene is expressed in terminal cells throughout the period of terminal branching. pruned encodes the Drosophila homologue of serum response factor (SRF), which functions with an ETS domain ternary complex factor as a growth-factor-activated transcription complex in mammalian cells. In pruned loss of function mutants, terminal cells fail to extend cytoplasmic projections. A constitutively activated SRF drives formation of extra projections that grow out in an unregulated fashion. An activated ternary complex factor has a similar effect. We propose that the Drosophila SRF functions like mammalian SRF in an inducible transcription complex, and that activation of this complex by signals from target tissues induces expression of genes involved in cytoplasmic outgrowth.

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