C75
Investigating the role of MDM2 in regulation of methylation
Maria Maguire, Paul Nield, Timothy Devling, Rosalind Jenkins, Kevin Park, Radoslaw Polanski, Triantafillos Liloglou, Carlos Rubbi, Nikolina Vlatkovic, Mark Boyd
University of Liverpool, Liverpool, UK
MDM2 up-regulation (often independent of p53 status) is associated with poor prognosis in a number of common cancers, notably in bladder, breast, renal and prostate. The mechanisms by which high MDM2 expression promotes oncogenesis independently of p53 are as yet undetermined. As MDM2 functions mainly via protein-protein interactions, we therefore attempted to identify proteins which bind MDM2 and thus may mediate these effects.
We discovered that DHFR interacts with MDM2 using an affinity chromatography approach combined with nano-LC-ESI MS/MS to identify potential MDM2 binding proteins. This result was corroborated using a yeast 2-hybrid screen. MDM2 binds directly to DHFR, monoubiquitylates it and inhibits its activity. Since folate metabolism is a target for chemotherapeutic intervention, we examined the effect of high level expression of MDM2 upon cellular sensitivity to methotrexate and found that elevated levels of MDM2 increased resistance to this drug. Thus MDM2 overexpression alters one carbon metabolism and this has consequences for processes regulation by methylation (Maguire et al Cancer Research 2008).
In follow-up studies, we have found that cells which express abnormally high levels of MDM2 are more resistant to the growth inhibitory effects of 5 azacytidine and recover more quickly from such treatment. Given the key roles that regulation of gene expression by DNA and protein methylation have in cellular systems, we are now investigating how MDM2 alters these in ways that contribute to its p53-independent oncogenicity.
