Suppression of p53 by Metastasis-Associated MAGE-A Proteins in melanoma

MAGE-A (melanoma antigen) proteins comprise a 12-member sub-family of cancer/testis (CT) antigens, so called because, physiologically, they are expressed almost exclusively in the testis, but during the development of a range of cancers (including melanoma where they were initially discovered) their expression is re-activated and is tightly associated with malignancy (i.e. with invasion and metastasis). Experimental evidence supports the idea that they are actually drivers of the malignant phenotype. We, and others, have established that several MAGE-A proteins are potent direct inhibitors of the p53 tumour suppressor and stimulate the levels of the crucial p53 inhibitor, MDM4.

We hypothesise that expression of MAGE-A proteins suppresses p53 tumour suppressor function during the development of melanoma, a form of cancer that generally retains wild type p53 status but frequently expresses high levels of MAGE-A proteins and MDM4. To explore this idea the project will identify amino acids in MAGE-A2 (as a representative member of the MAGE-A family) that are required to make contact with p53 and/or other key regulators of the p53 network. A series of MAGE-A2 mutants will be tested for their ability to associate with p53 in vitro (pulldown assays) and in cultured cells (co-immunoprecipitation assays). They shall also be tested functionally to determine whether they can mediate inhibition of p53 function/signalling, regulate MDM4 levels, and to block p53-mediated apoptosis. Based on these analyses, further fine-tuning analysis will be conducted by generating and testing appropriate point mutations. These analyses will be an integral component of ongoing studies aimed at establishing the mechanism of p53 inhibition by MAGE-A and identifying interacting regions/domains that can be explored as potential therapeutic targets.