Proteomic analysis of the signalling events involved in leukaemic transformation

by the tyrosine kinase fusion protein Tel/PDGFbR

Dr Helen Wheadon and Professor Anthony Whetton

The production of blood cells is a complex system, which is tightly controlled. There are several different types of blood cells and they have different functions; red blood cells carry oxygen around the body to the tissues, megakaryocytes produce platelets important for wound healing and clotting, and there are several different types of white blood cells which are involved in the immune response by fighting infection and disease. All of these different types of blood cells are produced by one single specialist cell called a stem cell. Stem cells are unusual as they have the ability to either self-renew, multiply, or mature down different pathways to produce the different blood cell types. This process occurs in the bone marrow and is controlled by molecules called growth factors, which act through specific receptors found on the cell surface. Once bound to the cell surface these growth factors trigger internal messages, which tell the cell either to self-renew, multiply or mature. Leukaemias are a group of diseases resulting in the abnormal production of any type of white blood cell. Several causes have been implicated in the disease progression including the repositioning of part of one chromosome next to part of another chromosome during cell division (chromosomal translocation). This, results in the production of an abnormal protein, which consists of part of one protein fused to part of another protein, some of these chimeric proteins have the ability to activate cells in the absence of growth factors. This project will use an established stem cell line derived from mice, which has been modified to express one such chimeric protein, an abnormal receptor, Tel/PDGFbR, implicated in chronic myelomonocytic leukaemia in humans. Tel/PDGFbR is an oncogene, which has the ability to trigger several different internal messages within the cell resulting in the accumulation of myeloid cells. This project will control the expressing of Tel/PDGFbR during the different stages of myeloid blood cell formation in order to study the effects this tyrosine kinase has on different proteins within the cells (proteomic analysis). Proteomic analysis is a technique, which will enable us to determine the role this oncogene is having globally on nearly all of the proteins within the cell. It will enable us to identify any oncogene-mediated changes in specific protein levels, alterations in their activation status and location within the cell, using state-of-the-art mass spectrometry. It is hoped that the application of proteomic approaches to this established system will enhance our understanding of the processes underlying haemopoietic cell development and leukaemogenesis.  At present patients with CMML and CML are treated with the drug, Imatinib. The introduction of this tyrosine kinase inhibitor has dramatically improved the treatment of these diseases as it targets the oncogenes, which cause them. Unfortunately over time some patients develop resistance to Imatinib, this has focused attention on targeting alternative proteins within the cells involved in signalling pathways identified in the disease progression, such as the Ras-ERK pathway. Indeed, we have already published data, using this system, which indicates that targeting both the tyrosine kinase activity of Tel/PDGFbR and the Ras/Erk pathway is a more effective strategy for complete reversal of the effects of this oncogene. We have also identified another pathway- the Wnt/GSK3/b-catenin, which appears to play an important role in this disease model. Combined therapy could, therefore, prevent drug resistance in the future. Understanding the internal processes involved in the progression of myeloid leukaemias is crucial for advances in their treatment and the identification of potential new targets for drug intervention. It is hoped that this study using a proteomic approach, will identify novel protein targets for drug intervention in the future.