We investigate how cancer-linked cell signal pathways interface with gene transcription and with the actin cytoskeleton, the cell’s major structural framework. We focus on two main signal pathways: the serum response factor (SRF) network and the Rho-actin signal pathway.
The SRF network
We study the mechanisms by which cellular signal transduction pathways cause specific activation of gene transcription. We focus on the transcriptional regulator serum response factor (SRF), first identified through our studies of the c-fos proto-oncogene, which controls both growth factor-regulated and muscle-specific genes.
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.
By contrast, members of the myocardin related transcription factor (MRTF) family (MRTF-A/MAL/MKL1, MRTF-B/MKL2 and myocardin) are either regulated through Rho GTPase signalling (MRTF-A and MRTF-B), or act constitutively (myocardin). The MRTFs are novel G-actin binding proteins, which sense changes in cellular G-actin concentration through their N-terminal RPEL domains.
The Rho-actin signal pathway
Activation of Rho GTPase signalling induces changes in actin treadmilling resulting in depletion of the cellular G-actin pool. This causes changes in the stoichiometry or amount of G-actin-RPEL protein complex, and changes in its activity.
Our current research on the SRF system focuses on the molecular analysis of the regulatory cofactors, and their role in Rho- and Ras-dependent processes including cell proliferation, adhesion and motility in both cancer and immune cell contexts.
A secondary interest in the lab concerns the analysis of other RPEL proteins, including the Phactr family of PP1 cofactors, whose activity is subject to control by variations in G-actin concentration.
We use approaches ranging from biochemistry, structural biology and cell biology to studies of cancer and immune mouse models in knockout mice. Our current studies focus on a number of areas:
- We use genomic 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.
- The role of the SRF network and Rho-actin signalling in cell behaviour, particularly cancer cell proliferation, invasion and metastasis, using cell biology approaches and mouse models.
- Other potential roles of actin as a regulatory factor, focussing on the regulation Phactr family of RPEL domain proteins, and two new families of novel RPEL proteins.
- Mice lacking the SRF network have severe defects in T cell development and function. We are using this system to investigate functional redundancy between the TCFs, and the connections between MAP kinase signalling, transcription, and cell differentiation.