SRF Co-factors Control the Balance between Cell Proliferation and Contractility

Abstract

SummaryThe ERK-regulated ternary complex factors (TCFs) act with the transcription factor serum response factor (SRF) to activate mitogen-induced transcription. However, the extent of their involvement in the immediate-early transcriptional response, and their wider functional significance, has remained unclear. We show that, in MEFs, TCF inactivation significantly inhibits over 60% of TPA-inducible gene transcription and impairs cell proliferation. Using integrated SRF ChIP-seq and Hi-C data, we identified over 700 TCF-dependent SRF direct target genes involved in signaling, transcription, and proliferation. These also include a significant number of cytoskeletal gene targets for the Rho-regulated myocardin-related transcription factor (MRTF) SRF cofactor family. The TCFs act as general antagonists of MRTF-dependent SRF target gene expression, competing directly with the MRTFs for access to SRF. As a result, TCF-deficient MEFs exhibit hypercontractile and pro-invasive behavior. Thus, competition between TCFs and MRTFs for SRF determines the balance between antagonistic proliferative and contractile programs of gene expression.

Mutual dependence of the MRTF–SRF and YAP–TEAD pathways in cancer-associated fibroblasts is indirect and mediated by cytoskeletal dynamics

“…The sensitivity of SRF binding to drug treatments likely reflects cooperative MRTF-SRF recruitment to promoters (Esnault et al 2014;Gualdrini et al 2016); the sensitivity TEAD4 binding to drug treatment is consistent with the YAP dependence of TEAD binding observed previously by others (Stein et al 2015) and may reflect either cooperative recruitment or nuclear export of TEAD4.…”

“…We compared that data set with our previous ChIP-seq (chromatin immunoprecipitation [ChIP] combined with highthroughput sequencing) analysis of MRTF-SRF target genes in serum-stimulated NIH3T3 fibroblasts (Esnault et al 2014;Gualdrini et al 2016). A substantial number of MRTF-SRF target genes, predominantly associated with cytoskeletal regulation, including the myofibroblast activation marker αSMA (Acta2), increased with severity of disease stage ( Fig.…”

“…Ideally, such definition requires identification of genomic binding sites for the factor concerned and a demonstration that transcription of genes that are in close proximity to these sites is dependent on the factor itself or the signal pathway that regulates it. Previously, we used this approach to define MRTF-SRF target genes in mouse NIH3T3 fibroblasts based on transcriptional response to MRTF-linked signals and proximity to MRTF-SRF genomic binding sites (Esnault et al 2014;Gualdrini et al 2016). The MRTF-SRF gene signature overlaps significantly with genes overexpressed in CAFs (Table 1A) as well as genes induced by YAP overexpression in different cell types (Table 1B, Dong et al 2007;Zhao et al 2008;Zhang et al 2009a;Cordenonsi et al 2011;Dupont et al 2011;Judson et al 2012).…”

“…Recent ChIP-seq studies have identified genomic binding sites for YAP-TEAD in normal and transformed human cells (Stein et al 2015;Zanconato et al 2015), many of which are associated with genes that are MRTF-SRF targets in fibroblasts (Table 1D; Esnault et al 2014;Gualdrini et al 2016). We further refined this analysis by integrating the IMR90 ChIP-seq data with an IMR90 Hi-C (chromosome capture followed by high-throughput sequencing) data set (Jin et al 2013) to identify genes whose transcription start sites (TSSs) are in physical contact with YAP-TEAD-binding sites.…”

FOXM1 is a critical driver of lung fibroblast activation and fibrogenesis

“…Although fibroblast proliferation and differentiation have been suggested as representing mutually exclusive cellular programs, this may represent an overly simplistic conceptualization. For example, serum-response factor, a transcription factor that has been shown to be instrumental in myofibroblast differentiation (44,45), has also been reported as regulating fibroblast proliferation (46,47). It is thus possible that these phenotypic programs are in fact interdependent and that ultimate-fate decisions depend on contextual cues that remain to be fully elucidated.…”