Title: Transcriptional responses to Ras and Rho signalling
Funder: The Francis Crick Institute

Abstract: Cellular signal transduction pathways cause specific activation of gene transcription, but much remains to be learned about the links between these responses and cell behaviour, and the mechanisms involved. We focus on the transcriptional regulator SRF, which controls proliferation and cell adhesion/migration, using cell models to analyse signalling mechanisms and immune cell and cancer models to examine its role in vivo. SRF activity is controlled through its association with two families of regulatory cofactors. The Ternary Complex Factor (TCF) family of Ets proteins - SAP-1, Elk-1 and Net - are controlled by phosphorylation of their C-terminal activation domains by MAP kinases. In contrast, members of the Myocardin Related Transcription Factor (MRTF) family - MRTF-A/MAL/MKL1, MRTF-B/MKL2 and myocardin - are either regulated through the novel Rho-actin signal pathway (MRTF-A and MRTF-B), or act constitutively (Myocardin). The MRTFs are G-actin binding proteins, which sense changes in cellular G-actin concentration through their N-terminal RPEL domains. Research on the SRF system focuses on the molecular analysis of the regulatory cofactors, and identification of their gene tartand their role in Rho- and Ras-dependent processes. To gain more insight into the biological significance of Rho-actin signalling, we also study other RPEL proteins. These include the Phactr family of PP1 cofactors, and two families of ArhGAP proteins. We use approaches ranging from biochemistry, structural biology and cell biology to studies of cancer and immune mouse models in knockout mice. We pursue several inter-related research topics:  SRF cofactor recruitment is gene-specific, and we are investigating the molecular basis for cofactor recruitment to SRF target genes. We are using genomic and biochemical approaches to assess the significance of signalling for events in transcriptional initiation and chromatin modification downstream of the MRTF and TCF cofactors.  The MRTF actin-binding RPEL domain controls nuclear import and export, phosphorylation, transcriptional activation, and possibly SRF interaction. We use structural, cell biological and biochemical approaches to study these regulatory events.  We are using genetic and phyical models to constrain cell movement in order to understand the involvement of the network in different modes of cell migration. We are using mouse cancer models to investigate the role of SRF in cancer cell proliferation, invasion and metastasis.  We are investigating the functional significance of G-actin binding to Phactr family proteins, with a focus on Phactr1. We are investigating the role of Phactrs in cell morphology, using MS-based approaches we have identified potential Phactr1 substrates, which we are using to probe the role of Phactrs in control of actin dynamics.  Using structural approaches we are characterising the interaction between the single RPEL repeat in ArhGAP12 with actin. Proteomics and cell imaging studies are being undertaken to investigate the functional significance of this interaction for regulation of actin dynamics.  Mice lacking the SRF network have severe defects in T cell development and function. We are investigating how the SRF network controls the response of T cells to immune challenge using Listeria models.


Research activity codes: 1.1 NORMAL BIOLOGICAL DEVELOPMENT AND FUNCTIONING;2.1 BIOLOGICAL AND ENDOGENOUS FACTORS
Health categories: CANCER AND NEOPLASMS;GENERIC HEALTH RELEVANCE