Signal Transduction Laboratory
Previous and current research
Our interests include the mechanisms by which cells respond to external signals that regulate their proliferation and survival, in particular the signalling pathways along which information is transferred leading from cell surface receptors to events in the cell nucleus, and how these are altered during the process of malignant transformation. We have characterised the molecular details of how Ras oncoproteins, which are mutationally activated in 30% of human tumours, are regulated and how they transmit their signal to the cell through direct binding to multiple effector proteins including Raf and phosphatidylinositol 3-kinase.
While the early signalling pathways activated by Ras are now well characterised and the changes in the gene expression programmes they induce have been documented, it remains a major challenge to understand later events in oncogene-induced signalling and which regulated genes are important in the establishment of the transformed phenotype. In order to investigate novel aspects of these pathways in cancer cells and to identify potential new targets for cancer therapies, we have employed a functional genomics approach using post-transcriptional gene silencing by genome-scale libraries of RNA interference agents. Two approaches to screening have been applied. In one, genes corresponding to a large fraction of the genome are systematically silenced one by one in a high throughput manner, allowing the identification of genes that are required for a particular aspect of the transformed phenotype to occur. In this way we have identified CUTL1, a transcription factor that is required for the metastatic behaviour of Ras transformed cells. In the second approach, many genes are silenced at the same time in a mixed pool of cells, with the selective screen being designed in such away that only cells acquiring the desired phenotype as a result of knock down of expression of one of these genes can survive. This type of screen has lead to the identification of MINK, a stress-induced protein kinase that may act as a tumour suppressor opposing Ras transformation in ovarian cancer.
Functional genomic drug resistance screens and CINATRA trial development
A recently completed RNA interference screen has identified regulators of mitotic arrest and ceramide metabolism as determinants of sensitivity to paclitaxel. We have identified 42 genes in common across 2 or more cancer cell lines which induce paclitaxel resistance when targeted by RNAi. All paclitaxel antagonists identified in this screen impair the ability of paclitaxel to induce a mitotic arrest. Over 70% of those selected for follow-up validation induce aneuploidy when silenced in the absence of drug.
We have also demonstrated a correlation between chromosomal numerical heterogeneity and taxane resistance in breast and colon cancer cell lines. Taken together with published work documenting the association of taxane resistance with aberrations in the spindle assembly checkpoint and the ability of near diploid microsatellite instability positive cell lines to arrest more efficiently in response to microtubule disruption than cell lines with chromosomal instability, we suggest this could be a compelling reason for the failure of taxanes to display activity in colorectal cancer with high frequency CIN.
A new microtubule stabiliser, EPO906 which evades MDR efflux membrane proteins, is currently the subject of a phase II clinical trial initiated in our laboratory which will soon commence recruitment at the Royal Marsden Hospital. This trial (CINATRA : Chromosomal Instability and Anti-Tubulin Response Assessment) aims to identify whether patients with metastatic colorectal cancer with near diploid MSI+ cancers and wild-type adenomatous polyposis coli gene product derive more benefit from EPO906 than patients with cancers which are chromosomally unstable (see CINATRA Trial Synopsis in left navigation for more information).
Future projects
We are using whole genome scale RNA interference libraries to identify new components of critical growth regulatory pathways. In addition we are screening for genes that are required for the survival of Ras transformed, but not normal, cells and also for genes that when disrupted may restore the sensitivity of drug resistant tumour cells to established chemotherapeutic agents.
