Regulation of the MRTF transcription factors by actin

A Crick PhD position for the 2021 programme in the lab of Richard Treisman.

Project background and description

Our laboratory studies a novel family of signal-responsive transcription factors, the MRTFs, and their upstream signalling pathway, the Rho-actin pathway. The MRTFs allow the gene transcription to be coordinated with alterations in the dynamics of the actin cytoskeleton induced by extracellular chemical or mechanical cues.

The MRTFs bind unpolymerised actin (G-actin) through a short sequence, the RPEL motif, that defines the RPEL protein family. 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. Our current model is that G-actin regulates MRTFs and other RPEL proteins by controlling their interactions with regulatory and effector proteins.

The project areas available include:

(i) The two MRTFs are transcriptional coactivators for the SRF transcription factor. Their nuclear accumulation is controlled by G-actin[1, 2]. The MRTFs control hundreds of genes, many of which build or regulate the actin cytoskeleton, and as a result, MRTF-null cells exhibit adhesion, motility and metastasis defects [3]. G-actin also controls MRTF activity in the nucleus, and we are using genomic and biochemical approaches to investigate two aspects of this: control of the access of MRTFs to DNA, and control productive transcription by RNA PolII. We are also developing methods to visualise where in the cell G-actin/RPEL protein interactions occur and how these interactions change in response to external signalling. We will use these to study the dynamics of MRTF activation in different cellular and regulatory contexts such as the cell cycle and mechanical stress.

(ii) The MRTF-SRF pathway is activated under conditions of mechanical stress, such as the increased tissue stiffening which accompanies cancer progression and fibrosis. We are interested in the mechanisms by which pathway activation is sensitised to mechanical stress in a cell specific manner, and the relation between MRTF-SRF signalling and another mechansensitive pathway, the YAP-TEAD pathway [4, 5] .

(iii) We also work on two other RPEL protein families, the four Phactrs - regulatory subunits of the PP1 phosphatase - and the ArhGAP12 family of Rho GTPase activating proteins [6, 7]. 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.

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.         Medjkane, S., Perez-Sanchez, C., Gaggioli, C., Sahai, E. and Treisman, R. (2009)

            Myocardin-related transcription factors and SRF are required for cytoskeletal dynamics and experimental metastasis.

            Nature Cell Biology 11: 257-268. PubMed abstract

4.         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

5.         Foster, C.T., Gualdrini, F. and Treisman, R. (2018)

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

            Genes & Development 31: 2361-2375. PubMed abstract

6.         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

7.         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