Treisman lab | The MRTF transcription factors, RPEL proteins and mechanobiology

A 2023 Crick PhD project with Richard Treisman.

Project background and description

Our laboratory studies the Rho-actin pathway, which plays a central role in cellular responses to growth factor signals and mechanical stress, and its targets, the RPEL proteins, which bind unpolymerised actin (G-actin). RPEL proteins play direct and indirect roles in the control of cytoskeletal behaviour and biological processes dependent on it, such as cell morphology and adhesion, and cancer invasion and metastasis. G-actin regulates RPEL protein activity either by modulating intramolecular interactions, or by binding competitively with RPEL protein effectors.

Our main focus is on the MRTFs, transcriptional coactivators for the SRF transcription factor, RPEL proteins whose nuclear accumulation is controlled by G-actin [1, 2]. The MRTFs allow gene transcription to be coordinated with cytoskeletal dynamics in response to growth factors and mechanical cues, controlling genes encoding cytoskeletal components and regulators [3]. As a result, MRTF-null cells exhibit adhesion, motility and metastasis defects. The MRTF-SRF pathway is activated under conditions of mechanical stress, such as the increased tissue stiffening which accompanies cancer progression and fibrosis.

Projects are available in the following areas:

(i) We have recently developed live-cell imaging methods that allow visualisation of the dynamics of rho-actin signalling in real time (R. Fedoryshchak, in preparation). We are using these to measure pathway activity in different cell compartments in different cell types and culture settings. We are particularly interested to elucidate the role played by rho-actin signalling to the MRTFs in control of fibroblast cell cycle progression, CAF-dependent tumor progression, and mesenchymal stem cell differentiation. We are also interested in how MRTF-SRF signalling interacts with another mechansensitive pathway, the YAP-TEAD pathway.

(ii) We continue to study the molecular basis of MRTF regulation by G-actin. We recently identified a new mechanism by which G-actin controls MRTF activity. We are using genomic and biochemical, structural and genomic approaches to investigate how it controls access of MRTFs to SRF and DNA, and productive transcription by RNA PolII.

(iii) We also study two other RPEL protein families, the four Phactrs - regulatory subunits of the PP1 phosphatase - and the ArhGAP12 family of Rho GTPase activating proteins [4, 5]. We use cell biological and mouse model approaches to study how these proteins control cytoskeletal events, and to understand the functional significance of the coupling of the activity to actin dynamics.

Projects utilise a wide variety of experimental approaches including molecular cell biology, functional genomics and global analysis of gene expression, siRNA screening, biochemical and structural studies, and mouse models. The precise project pursued for PhD will be decided on in consultation with RT.

Candidate background

Candidates should have a background in biochemistry or molecular cell biology. They should be motivated by a strong interest in understanding the mechanisms that underpin fundamental cellular processes, and the desire to elucidate them in molecular detail. They will have at least some experience with molecular biology, cloning, and cell culture, and be prepared to extend their technical repertoire according to the demands of the project.

References 

1.       Vartiainen, M.K., Guettler, S., Larijani, B. and Treisman, R. (2007)

          Nuclear actin regulates dynamic subcellular localization and activity of the SRF cofactor MAL.

          Science 316: 1749-1752. PubMed abstract

2.       Mouilleron, S., Langer, C.A., Guettler, S., McDonald, N.Q. and Treisman, R. (2011)

          Structure of a pentavalent G-actin•MRTF-A complex reveals how G-actin controls nucleocytoplasmic shuttling of a transcriptional coactivator.

          Science Signaling 4: ra40. PubMed abstract

3.       Gualdrini, F., Esnault, C., Horswell, S., Stewart, A., Matthews, N. and Treisman, R. (2016)

          SRF co-factors control the balance between cell proliferation and contractility.

          Molecular Cell 64: 1048-1061. PubMed abstract

4.       Diring, J., Mouilleron, S., McDonald, N.Q. and Treisman, R. (2019)

          RPEL-family rhoGAPs link Rac/Cdc42 GTP loading to G-actin availability.

          Nature Cell Biology 21: 845-855. PubMed abstract

5.       Fedoryshchak, R.O., Přechová, M., Butler, A.M., Lee, R., O'Reilly, N., Flynn, H.R., . . . Treisman, R. (2020)

          Molecular basis for substrate specificity of the Phactr1/PP1 phosphatase holoenzyme.

          eLife 9: e61509. PubMed abstract