Serum response factor is crucial for actin cytoskeletal organization and focal adhesion assembly in embryonic stem cells

Abstract

The activity of serum response factor (SRF), an essential transcription factor in mouse gastrulation, is regulated by changes in actin dynamics. Using Srf(−/−) embryonic stem (ES) cells, we demonstrate that SRF deficiency causes impairments in ES cell spreading, adhesion, and migration. These defects correlate with defective formation of cytoskeletal structures, namely actin stress fibers and focal adhesion (FA) plaques. The FA proteins FA kinase (FAK), β1-integrin, talin, zyxin, and vinculin were downregulated and/or mislocalized in ES cells lacking SRF, leading to inefficient activation of the FA signaling kinase FAK. Reduced overall actin expression levels in Srf(−/−) ES cells were accompanied by an offset treadmilling equilibrium, resulting in lowered F-actin levels. Expression of active RhoA-V14 rescued F-actin synthesis but not stress fiber formation. Introduction of constitutively active SRF-VP16 into Srf(−/−) ES cells, on the other hand, strongly induced expression of FA components and F-actin synthesis, leading to a dramatic reorganization of actin filaments into stress fibers and lamellipodia. Thus, using ES cell genetics, we demonstrate for the first time the importance of SRF for the formation of actin-directed cytoskeletal structures that determine cell spreading, adhesion, and migration. Our findings suggest an involvement of SRF in cell migratory processes in multicellular organisms.

BARX2 and estrogen receptor-α (ESR1) coordinately regulate the production of alternatively spliced ESR1 isoforms and control breast cancer cell growth and invasion

“…BARX2 might promote serum-dependent migration by any of these mechanisms. For example, BARX2 influences the cytoskeleton (Meech et al, 2003) and interacts with the serum response factor (SRF) (Herring et al, 2001), which controls actin-directed cell spreading (Schratt et al, 2002). BARX2 also increases transcription of MMP9, which is known to promote invasion of cancer cells via matrix degradation (Vu et al, 1998;Balduyck et al, 2000;Zhao et al, 2004).…”

Restricted inactivation of serum response factor to the cardiovascular system

“…Previous studies in embryonic stem cells null for SRF showed defects in cell migration, presumably as a result of a disrupted cytoskeleton (6). Interestingly, flies and social amoeba null for SRF also display defects in cell migration that are thought to be a result of an altered cytoskeleton (5,28).…”

“…One or more CArG boxes (consensus ϭ CCW 6 GG) are found within the proximal promoter or first intron of Ͼ60 SRF-dependent genes, half of which are restricted to cardiac, skeletal, and smooth muscle (SM) cells (SMCs) (1,2). Genetic inactivation of SRF in amoeba (3), worm (4), fly (5), and mouse embryonic stem cells (6) has confirmed a critical role for SRF in normal cytoskeletal architecture, cell adhesion, cell migration, and͞or animal movement. These results are consistent with data in transgenic reporter mice showing the functional importance of CArG elements in muscle promoter activity (2,7).…”

Cellular micro-environments reveal defective mechanosensing responses and elevated YAP signaling in LMNA-mutated muscle precursors

“…There is growing evidence that the integrity of the nucleus (Lammerding et al, 2004;Lammerding et al, 2005;Hale et al, 2008) and mechanotransduction signaling (Lammerding et al, 2005;Emerson et al, 2009) might be impaired in the diseases linked to mutations in A-type lamins and lamin-associated proteins. Recent major findings from the Lammerding group show that cells and cardiac tissue from A-type lamin mutant mice have impaired nuclear translocation and downstream signaling of megakaryoblastic leukemia 1 protein (MKL1, also known as MRTF-A and MAL) (Ho et al, 2013), a transcription factor which regulates, through serum response factor (SRF), the expression of signaling molecules, transcription factors and numerous cytoskeletal components, including actin genes, nonmuscle myosins and vinculin (Schratt et al, 2002;Cen et al, 2003;Miralles et al, 2003). Deregulation of MKL1-SRF signaling is attributed to changes in actin dynamics in lamin A/C mutant mouse embryonic fibroblasts (MEFs) (Ho et al, 2013).…”