Targeting addiction to a breast cancer metastasis survival pathway by inhibition of RAN GTPase
Metastatic cancer is a major global health burden. Each year, eleven million new cases of cancer are diagnosed worldwide, including 5 million cases in industrialized countries. In 2009, 7.6 million people worldwide died of cancer, while one in three of us will develop cancer during our lifetime. Patients with breast and other common cancers often do not die from their primary tumour, but rather from disseminated disease, usually as a consequence of development of resistance to existing cancer therapies. So far, there are no available drugs for the prevention or arrest of tumour metastasis. Consequently, the long-term outcome for patients with aggressive malignant tumours is generally very poor. Better methods for early diagnosis and preventing tumour spread to other organs would save and prolong the life of patients. Central to therapeutic advancements of this type are: (i) developing molecular-targeted therapies to overcome the common problem of drug resistance; and (ii) developing novel therapies that specifically target and destroy tumour cells but leave normal cells undamaged.
Training provided through this studentship programme is critical for the development of new and better-trained researchers who will investigate approaches for the prevention cancer metastasis. PEA3, osteopontin (OPN), c-Met, c-Myc, SGK1 and Ran GTPase (RAN) are proteins and enzymes that comprise a “Ran Signalling axis” (RanAXIS). This axis is made up of a netwrok of genes and proteins that are novel therapeutic targets in breast cancer. This project will investigate the impact of the RanAXIS on cellular processes and molecular phenotypes in cell lines and human tissues, enabling the development of targeted therapies and companion biomarkers. This will provide an excellent background for the comprehensive training of PhD student.
El-Tanani laboratory has identified Ran as a major downstream target for OPN. Moreover, Ran is overexpressed in various cancers, and this overexpression is correlated with increased aggressiveness of the cancer cells in vitro and in vivo. We, and others have also shown that silencing RAN expression induces more apoptosis in cancer cells compared to normal cells. These results therefore suggest that RAN is a potential therapeutic target for breast cancer. RAN regulates nucleocytoplasmic transport, and it is therefore an established master regulator of many oncogene-related pathways, with emerging defined roles in apoptosis and metastasis. RAN also regulates cell division and can promote genetic instability in cells, when its expression is deregulated. Cancer cell proliferation is dependent on RAN activity. This highlights the dual nature of RAN as a driver of genetic instability when aberrantly expressed - hence a potential prognostic marker - and yet an Achilles’ heel - hence a potential therapeutic target. RAN and the components of its regulatory and effector network, RANAXIS, are widely implicated in cancer biology. However, no systematic studies have yet been undertaken to relate RAN expression levels and activity to the aggressiveness of cancer and metastatic disease, or to the cellular response to existing therapy. We used comparative DNA microarray analysis of MDA-MB-231 cells with or without stable RAN shRNA silencing to identify the genes regulated by RAN. We found that the genes encoding BR serine/threonine kinase 1 (BRSK1), Activating Transcription Factor 3 (ATF3), YOD1, MMP11, MMP24, METL7A, ADAMTS6, SOCS7 and MKNK2 are dysregulated following RAN silencing.
Principal Hypothesis: The RAN pathway is a potential therapeutic target for breast cancer.
AIM 1: Investigate the molecular mechanisms involved in the RANAXIS: To develop an in-depth molecular understanding of how elevated RAN expression alters cell phenotypes and to identify points at which RAN-targeted therapeutic intervention is effective. Strategies for direct modulation of RANAXIS in cell lines have already been established in the El-Tanani laboratory.
AIM 2: Investigate the interrelation between RAN and its targets in regulating fundamental mechanisms of metastatic transformation: The roles of RAN and selected target genes on metastasis will be investigated by up- and down-regulating their expression using tetracycline-inducible gene/shRNA expression systems and assessing what impact this has on cell proliferation, adhesion, invasive/migration, detachment-induced apoptosis (anoikis) and colony formation in vitro and metastasis in vivo.
AIM 3: Biomarker discovery in the RANAXIS for drug monitoring and patient prognosis: Determination of the relationship between overexpression of the biomarker proteins in retrospective primary breast tumours with patient outcome using immunohistochemistry (IHC).