I have recently completed my D.Phil in the department of Paediatrics at the University of Oxford under the supervision of Dr Chris Mitchell. The title of my thesis is The Characterisation of the Differences in Gene Expression between Rhabdomyosarcoma cells and myoblasts. The purpose of this project was to see if we could find any differences between cancer cells and normal cells. I focused on the childhood malignancy called Rhabdomyosarcoma (RMS) which accounts for 5-8% of childhood cancer. Two different types of RMS exist; one type is called embryonal RMS (ERMS) usually affecting young children and associated with a good survival rate, and the other type is called alveolar RMS (ARMS) affecting older children with a much poorer survival rate. One very obvious difference between these types of RMS is the development of metastases in patients suffering with ARMS. Metastasis describes the process where by some of the cancer cells have been able to “break away” from the primary tumour, circulate through the bloodstream and grow in other normal tissues elsewhere in the body.
The first part of my study was to look at general changes in the expression of genes in cancer cells and in normal cells called myoblasts (a type of early muscle cell). I used two techniques – called representational difference analysis and microarrays. In both these techniques the cancer cells and normal cells are labelled differently, for example with different colours, making it possible to compare the amount of a gene in each different cell type. In this way, we can identify genes that are found at higher levels in the cancer cells and at lower levels in the normal cells that may be important in how a cancer cell develops. The main findings from these experiments were the over expression of genes in the cancer cells responsible for increasing cell proliferation and division, and genes that enable the cancer cells to evade mechanisms that would stop such uncontrolled cell division. The results also highlighted which gene pathways and networks are affected in the cancer cells, again providing more clues about what drives a normal cell to become a cancer cell. In addition a group of closely related genes were only found in ERMS cells and not ARMS cells, so these genes could be used as markers to help us distinguish ERMS from ARMS.
Approximately 90% of all cancer deaths are due to metastases, and as mentioned before ARMS are often associated with metastatic spread. Therefore the second part of my project focussed on investigating genes involved in allowing a cell to travel around the body, settle in a tissue and then grow into another tumour. Two genes, called ELMO1 and NELL1, were found at much higher levels in ARMS cells compared to ERMS cells and normal myoblasts, and have previously been implicated in cell migration and invasion. Experiments were set up to show that if ELMO1 and NELL1 were put into a cell that does not normally express these genes, the characteristics of that cell changed. The cells were now able to migrate. Similarly, stopping the expression of ELMO1 in ARMS cells by ‘silencing’ this gene caused these cells to lose their ability to migrate. Consequently ELMO1 could be a potential therapeutic target in the treatment of ARMS.
Although I have now finished my PhD, we hope to write up and publish the results from our metastasis work. Also, with the appointment of a new Professor of Paediatric Oncology in Oxford, we hope that the research on rhabdomyosarcomas will continue and there are already plans to set up a William Dodd Fellowship for another PhD student.
Elizabeth Rapa, 9th October 2008