scholarly journals Myocardin-Related Transcription Factor A Activation by Competition with WH2 Domain Proteins for Actin Binding

2016 ◽  
Vol 36 (10) ◽  
pp. 1526-1539 ◽  
Author(s):  
Julia Weissbach ◽  
Franziska Schikora ◽  
Anja Weber ◽  
Michael Kessels ◽  
Guido Posern
Keyword(s):  
Serum Response Factor ◽  
De Novo ◽  
Actin Dynamics ◽  
Actin Binding ◽  
Serum Stimulation ◽  
Competitive Mechanism ◽  
Related Transcription Factor ◽  
Simultaneous Inhibition ◽  
Serum Response

The myocardin-related transcription factors (MRTFs) are coactivators of serum response factor (SRF)-mediated gene expression. Activation of MRTF-A occurs in response to alterations in actin dynamics and critically requires the dissociation of repressive G-actin–MRTF-A complexes. However, the mechanism leading to the release of MRTF-A remains unclear. Here we show that WH2 domains compete directly with MRTF-A for actin binding. Actin nucleation-promoting factors, such as N-WASP and WAVE2, as well as isolated WH2 domains, including those of Spire2 and Cobl, activate MRTF-A independently of changes in actin dynamics. Simultaneous inhibition of Arp2-Arp3 or mutation of the CA region only partially reduces MRTF-A activation by N-WASP and WAVE2. Recombinant WH2 domains and the RPEL domain of MRTF-A bind mutually exclusively to cellular and purified G-actinin vitro. The competition by different WH2 domains correlates with MRTF-SRF activation. Following serum stimulation, nonpolymerizable actin dissociates from MRTF-A, andde novoformation of the G-actin–RPEL complex is impaired by a transferable factor. Our work demonstrates that WH2 domains activate MRTF-A and contribute to target gene regulation by a competitive mechanism, independently of their role in actin filament formation.

scholarly journals Nuclear-capture of endosomes depletes nuclear G-actin to promote SRF/MRTF activation and cancer cell invasion

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Sergi Marco ◽  
Matthew Neilson ◽  
Madeleine Moore ◽  
Arantxa Perez-Garcia ◽  
Holly Hall ◽  
...  
Keyword(s):  
Nuclear Import ◽  
Tyrosine Kinases ◽  
Target Genes ◽  
Serum Response Factor ◽  
Actin Binding ◽  
Cell Scattering ◽  
Nuclear Localisation Sequence ◽  
Related Transcription Factor ◽  
Endosomal System ◽  
Serum Response

AbstractSignals are relayed from receptor tyrosine kinases (RTKs) at the cell surface to effector systems in the cytoplasm and nucleus, and coordination of this process is important for the execution of migratory phenotypes, such as cell scattering and invasion. The endosomal system influences how RTK signalling is coded, but the ways in which it transmits these signals to the nucleus to influence gene expression are not yet clear. Here we show that hepatocyte growth factor, an activator of MET (an RTK), promotes Rab17- and clathrin-dependent endocytosis of EphA2, another RTK, followed by centripetal transport of EphA2-positive endosomes. EphA2 then mediates physical capture of endosomes on the outer surface of the nucleus; a process involving interaction between the nuclear import machinery and a nuclear localisation sequence in EphA2’s cytodomain. Nuclear capture of EphA2 promotes RhoG-dependent phosphorylation of the actin-binding protein, cofilin to oppose nuclear import of G-actin. The resulting depletion of nuclear G-actin drives transcription of Myocardin-related transcription factor (MRTF)/serum-response factor (SRF)-target genes to implement cell scattering and the invasive behaviour of cancer cells.

scholarly journals Lamina-associated polypeptide 2α is required for intranuclear MRTF-A activity

2021 ◽  
Author(s):  
Ekaterina Sidorenko ◽  
Maria Sokolova ◽  
Antti Pennanen ◽  
Salla Kyheroinen ◽  
Guido Posern ◽  
...  
Keyword(s):  
Target Genes ◽  
Serum Response Factor ◽  
Actin Dynamics ◽  
Chromatin Binding ◽  
Binding Partner ◽  
Related Transcription Factor ◽  
Direct Binding ◽  
Efficient Expression ◽  
Serum Response

Myocardin-related transcription factor A (MRTF-A), a coactivator of serum response factor (SRF), regulates the expression of many cytoskeletal genes in response to cytoplasmic and nuclear actin dynamics. Here we describe a novel mechanism to regulate MRTF-A activity within the nucleus by showing that lamina-associated polypeptide 2α (Lap2α), the nucleoplasmic isoform of Lap2, is a direct binding partner of MRTF-A, and required for the efficient expression of MRTF-A/SRF target genes. Mechanistically, Lap2α is not required for MRTF-A nuclear localization, unlike most other MRTF-A regulators, but is required for binding of MRTF-A to its target genes. This regulatory step takes place prior to MRTF-A chromatin binding, because Lap2α neither interacts with, nor specifically influences active histone marks on MRTF-A/SRF target genes. Phenotypically, Lap2α is required for serum-induced cell migration, and deregulated MRTF-A activity may also contribute to muscle and proliferation phenotypes associated with loss of Lap2α. Our studies therefore add another regulatory layer to the control of MRTF-A-SRF-mediated gene expression, and broaden the role of Lap2α in transcriptional regulation.

Actin-mediated gene expression in neurons: the MRTF-SRF connection

2010 ◽  
Vol 391 (6) ◽  
Author(s):  
Bernd Knöll
Keyword(s):  
Gene Expression ◽  
Nervous System ◽  
Serum Response Factor ◽  
Actin Dynamics ◽  
Response Factor ◽  
Related Transcription Factor ◽  
Gene Regulatory ◽  
Regulatory Loop ◽  
Serum Response ◽  
Prime Target

Abstract The traditional view of cellular actin is a rather autarkic cytoskeletal framework function confined to the cytoplasm. However, there is now evidence that alterations in actin dynamics are sensed by the nucleus and subsequently modulate gene expression. In communicating with the nucleus, cytoplasmic, and most likely also nucleus-resident actin, provides a further (gene) regulatory loop to cell motility. A transcription module composed of MRTF (myocardin-related transcription factor) and SRF (serum response factor) emerges as prime target of such actin signaling. Here, I focus on the nervous system, where the actin-MRTF-SRF entity governs multiple aspects of neuronal motility.

scholarly journals The Stress-Inducible Protein DRR1 Exerts Distinct Effects on Actin Dynamics

2018 ◽  
Vol 19 (12) ◽  
pp. 3993 ◽  
Author(s):  
Anja Kretzschmar ◽  
Jan-Philip Schülke ◽  
Mercè Masana ◽  
Katharina Dürre ◽  
Marianne B. Müller ◽  
...  
Keyword(s):  
Molecular Mechanisms ◽  
Serum Response Factor ◽  
Coiled Coil ◽  
Stress Physiology ◽  
Actin Dynamics ◽  
Actin Binding ◽  
Nucleation Effect ◽  
Cytoskeletal Dynamics ◽  
Vitro Analysis

Cytoskeletal dynamics are pivotal to memory, learning, and stress physiology, and thus psychiatric diseases. Downregulated in renal cell carcinoma 1 (DRR1) protein was characterized as the link between stress, actin dynamics, neuronal function, and cognition. To elucidate the underlying molecular mechanisms, we undertook a domain analysis of DRR1 and probed the effects on actin binding, polymerization, and bundling, as well as on actin-dependent cellular processes. Methods: DRR1 domains were cloned and expressed as recombinant proteins to perform in vitro analysis of actin dynamics (binding, bundling, polymerization, and nucleation). Cellular actin-dependent processes were analyzed in transfected HeLa cells with fluorescence recovery after photobleaching (FRAP) and confocal microscopy. Results: DRR1 features an actin binding site at each terminus, separated by a coiled coil domain. DRR1 enhances actin bundling, the cellular F-actin content, and serum response factor (SRF)-dependent transcription, while it diminishes actin filament elongation, cell spreading, and actin treadmilling. We also provide evidence for a nucleation effect of DRR1. Blocking of pointed end elongation by addition of profilin indicates DRR1 as a novel barbed end capping factor. Conclusions: DRR1 impacts actin dynamics in several ways with implications for cytoskeletal dynamics in stress physiology and pathophysiology.

scholarly journals Transcriptional responses to hyperplastic MRL signalling in Drosophila

Open Biology ◽  
2017 ◽  
Vol 7 (2) ◽  
pp. 160306 ◽  
Author(s):  
Vincent Jonchère ◽  
Nada Alqadri ◽  
John Herbert ◽  
Lauren Dodgson ◽  
David Mason ◽  
...  
Keyword(s):  
Serum Response Factor ◽  
Transcriptional Response ◽  
Size Control ◽  
Actin Dynamics ◽  
Transcriptional Responses ◽  
Rna Profiling ◽  
Related Transcription Factor ◽  
Transcriptional Changes ◽  
Wing Discs

Recent work has implicated the actin cytoskeleton in tissue size control and tumourigenesis, but how changes in actin dynamics contribute to hyperplastic growth is still unclear. Overexpression of Pico, the only Drosophila Mig-10/RIAM/Lamellipodin adapter protein family member, has been linked to tissue overgrowth via its effect on the myocardin-related transcription factor (Mrtf), an F-actin sensor capable of activating serum response factor (SRF). Transcriptional changes induced by acute Mrtf/SRF signalling have been largely linked to actin biosynthesis and cytoskeletal regulation. However, by RNA profiling, we find that the common response to chronic mrtf and pico overexpression in wing discs was upregulation of ribosome protein and mitochondrial genes, which are conserved targets for Mrtf/SRF and are known growth drivers. Consistent with their ability to induce a common transcriptional response and activate SRF signalling in vitro , we found that both pico and mrtf stimulate expression of an SRF-responsive reporter gene in wing discs. In a functional genetic screen, we also identified deterin , which encodes Drosophila Survivin, as a putative Mrtf/SRF target that is necessary for pico -mediated tissue overgrowth by suppressing proliferation-associated cell death. Taken together, our findings raise the possibility that distinct targets of Mrtf/SRF may be transcriptionally induced depending on the duration of upstream signalling.

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 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 Villin Severing Activity Enhances Actin-based Motility In Vivo

2007 ◽  
Vol 18 (3) ◽  
pp. 827-838 ◽  
Author(s):  
Céline Revenu ◽  
Matthieu Courtois ◽  
Alphée Michelot ◽  
Cécile Sykes ◽  
Daniel Louvard ◽  
...  
Keyword(s):  
Shigella Flexneri ◽  
Actin Dynamics ◽  
Actin Binding ◽  
Loss Of Function ◽  
Mesenchymal Transition ◽  
Capping Protein ◽  
Function Strategy ◽  
In Cells

Villin, an actin-binding protein associated with the actin bundles that support microvilli, bundles, caps, nucleates, and severs actin in a calcium-dependant manner in vitro. We hypothesized that the severing activity of villin is responsible for its reported role in enhancing cell plasticity and motility. To test this hypothesis, we chose a loss of function strategy and introduced mutations in villin based on sequence comparison with CapG. By pyrene-actin assays, we demonstrate that this mutant has a strongly reduced severing activity, whereas nucleation and capping remain unaffected. The bundling activity and the morphogenic effects of villin in cells are also preserved in this mutant. We thus succeeded in dissociating the severing from the three other activities of villin. The contribution of villin severing to actin dynamics is analyzed in vivo through the actin-based movement of the intracellular bacteria Shigella flexneri in cells expressing villin and its severing variant. The severing mutations abolish the gain of velocity induced by villin. To further analyze this effect, we reconstituted an in vitro actin-based bead movement in which the usual capping protein is replaced by either the wild type or the severing mutant of villin. Confirming the in vivo results, villin-severing activity enhances the velocity of beads by more than two-fold and reduces the density of actin in the comets. We propose a model in which, by severing actin filaments and capping their barbed ends, villin increases the concentration of actin monomers available for polymerization, a mechanism that might be paralleled in vivo when an enterocyte undergoes an epithelio-mesenchymal transition.

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