Title: Understanding molecular mechanisms & consequences of TGF beta/BMP signal transduction pathways in cells & human diseases
Funder: Medical Research Council

Abstract: The TGF beta family of ligands, including BMP, control multiple cellular processes including cell proliferation, recognition, differentiation, apoptosis, and cell fate and their malfunctions cause human disorders ranging from bone defects to cancer progression and metastasis. Smad proteins transduce BMP and TGF beta signals upon phosphorylation of their C-terminal SXS motif by receptor kinases, leading to their interaction with Smad4 and translocation to the nucleus, where they regulate the expression of hundreds of genes. The activity of Smad1/5/8 in the BMP pathway and Smad2/3 in the TGF beta pathway is regulated by pathway crosstalk and feedback inputs through multiple signalling pathways. We are interested in elucidating molecular mechanisms by which TGF beta and BMP signalling networks are modulated by inputs from other signalling pathways, especially in the context of development and human diseases, including bone diseases and cancer. The specific research objectives currently being undertaken are as follows:||1. Integration of signalling networks at the level of Smads: Much is known about individual linear signalling pathways downstream of specific hormones, growth factors and cytokines. In the context of complex cellular processes and disease, multiple signalling networks are at play and it is this interplay that determines the outcome in a given context. We are interested in addressing how different signalling inputs affect the outcome of BMP/TGF beta signalling. By employing proteomic approaches, we aim to identify novel interacting partners for Smad proteins downstream of different factors in different biological contexts. Preliminary experiments have resulted in the identification of some novel Smad-interacting proteins as well as some established Smad-interacting partners. We will also identify modifications introduced by specific factors within the Smad proteins or their interacting partners. Extensive functional tests on novel interacting partners will be performed using cell-based assays including stem cells, in a developmental context using Xenopus embryos, in mice using targeted gene disruption strategies and in relevant human disease models.||2. Regulation of Smad dephosphorylation and termination of Smad signalling: Dephosphorylation and recycling of activated Smads is an integral part of TGF beta signalling and critical for agonist sensing by the cell. We identified and characterized the SCP family of nuclear phosphatases as mediators of Smad1-tail dephosphorylation in the BMP signalling pathway as well as linker regions of Smad1 and Smad2/3. In addition to SCPs as Smad1-tail and Smad1/2/3-linker phosphatases, PPM1A and PDP have been reported as Smad1/2 phosphatases. The precise molecular details of exactly when, where, how, and by which phosphatase, the dephosphorylation of Smads takes place is still unresolved. Most phosphatases have multiple substrates and depend on cofactors to define specificity towards individual substrates. We are interested in identifying rate-limiting factors for some of these phosphatases. SCP2 is overexpressed in numerous sarcomas as well as brain tumours. We will investigate whether the overexpression is linked to deregulation of BMP signalling in these cancers or derivative cell lines and will also determine what effect, if any, knocking down SCP2 in these cells has on their proliferation rates, migration and BMP signalling.||3. Regulation of Smad stability by ubiquitination: Smurf1 is dependent on linker phosphorylation of proline-directed sites to recognize and ubiquitinate Smad1. We are interested in resolving the molecular basis and determinants of this interaction. In addition we are interested in identifying novel substrates for Smurf1/2 based on their substrate recognition by phosphorylation of substrates at proline-directed sites, in addition to the presence of the classical PY motifs. Aberrant Smurf1/2 action has been reported in pancreatic cancer, which is also m


Research activity codes: 1.1 NORMAL BIOLOGICAL DEVELOPMENT AND FUNCTIONING
Health categories: GENERIC HEALTH RELEVANCE