Richard Treisman

Signal transduction and transcription

Research in the laboratory is focussed on the relationship between signalling pathways, the cytoskeleton, and transcriptional regulation. We focus on Serum Response Factor (SRF), which controls many growth factor-regulated and muscle-specific genes¹. SRF activity is regulated by its mutually exclusive interaction with two different families of regulatory cofactors whose activity is controlled by diverse cellular signalling pathways: the myocardin family (myocardin, MAL/MKL1 and MAL16/MKL2); and the ternary complex factor (TCF) family of Ets domain proteins (Elk-1, SAP-1 and Net /SAP-2).

Previous studies in our laboratory showed that small GTPases of the Rho family control SRF activity by inducing depletion of the G-actin pool^2-5. Recently we showed that the myocardin-related protein MAL/MKL1, which is rearranged in t(1;22)(p13;q13) M7 type AML, is a G-actin-binding SRF coactivator which is redistributed from cytoplasm to nucleus upon activation of actin polymeriation. In addition, MAL is phosphorylated by both Rho-dependent and ERK-dependent signalling pathways⁶.

The TCFs are regulated by MAP kinases through through phosphorylation of their C-terminal regulatory domain¹. Our studies here concentrate on the understanding the significance of TCF signalling in a biological context.

The laboratory uses a variety of approaches, including mammalian cell transfection, yeast two-hybrid assays, FACS analysis, immunofluorescence microscopy, microarray analysis, ES cells and mouse knockouts, and other molecular and cell biological techniques.

Molecular analysis of MAL / MKL1 and its relatives
We wish to understand the sequences of MAL (and other family members) involved in interaction with actin, and the nature of the changes in MAL-actin interaction which take place upon signalling. A number of actin mutants with novel properties have been identified and we will also be investigating the nature of the MAL-SRF interaction and its effects on DNA sequence specificity. Both of these projects will be carried through to structural analysis.

Functional studies of MAL and SRF are examining the relationship between nuclear localisation of MAL and transcriptional activation of SRF target genes, mapping the sites of MAL phosphorylation other post-translational modifications. MAL-interacting and -modifying proteins and regulatory complexes are being characterised and their functional relevance to transcriptional regulation and to MAL-induced transformation will be examined.

At the cell biological level a number of lines of investigation are being pursued. We wish to understand where in the cell MAL activation takes place, and to elucidate the mechanism by which MAL is imported into and re-exported from the nucleus. The biological significance of the Rho-SRF pathway in cell-cell interactions, cell motility and cell migration is being investigated with an emphasis on its role in transformation. We are also investigating a second family of proteins which responds to alterations in G-actin level, with a view to understanding how cellular behaviour responds to changes in the actin cytoskeleton.

SAP-1 and the TCF proteins in immunology and cancer
We have used ES technology to inactivate the SAP-1 TCF in the mouse to investigate the developmental role of this TCF. Mice lacking SAP-1 are viable and fertile. They appear susceptible to infection, and develop symptoms similar to those of human Castleman's disease. Mice lacking SAP-1 exhibit severe defects in thymocyte selection⁷. Future experiments will focus on in-depth analysis of the role of SAP-1 in immune system, the characterisation of other aspects of the SAP-1 immune phenotype, and the relevance of TCF signalling for transformation. Studies of mice lacking multiple TCF family members are being conducted in collaboration with groups in Germany and France.

References

1. Treisman R. EMBO J 1995; 14: 4905-4913.
2. Sotiropoulos A,et al. Cell 1999; 98: 159-169.
3. Copeland J and Treisman R. Mol Biol Cell 2002; 13: 4088-4099
4. Posern G, et al. Mol Biol Cell 2002; 13: 4167-4178.
5. Grosse R,et al. EMBO J 2003; 22: 3050-3061.
6. Miralles F, et al. Cell 2003; 113: 329-342.
7. Posern G, et al. EMBO J 2004; 23: 3973-3983.
8. Costello PS, et al. Nature Immunology 2004; 5: 289-298.