Initial characterization of MageC2 tumor protein

TOLEDO MF; LAISECA JE; MONTE M; PASCUCCI, FRANCO; LADELFA MF

Mar del Plata

Congreso; Reunión Anual de la SAIC; 2016

MAGE-I (Melanoma Antigen GEnes) are expressed in tumors, placenta and germ line cells. Since MAGE-I proteins are highly homologous, it has been suggested that could display a redundant function. We and others have presented evidence pointing to specificity rather than redundancy in many cases. In this work we pointed to the initial characterization of MageC2 function by comparing to the activity of already established MAGE-I proteins. We first determined that MageC2 is a nuclear localized protein with a molecular weight of 55KDa approximately. This localization is different to that observed for MageB2 (nucleolar) but similar to MageA2 and MageA11.With the aim to evaluate it function, we compared MageC2 activity to that of MageA2 as inhibitor of p53 and MageA11 as coactivator of the androgen receptor, AR. We performed specific reporter gene assay to analyze the effect of MageC2 on p53 (pG13-LUC reporter) and AR activity (pPSA-LUC reporter). Our results indicated that MageC2 exerts no significant induction on AR (1,3 fold increase) as compared to MageA11 (4,2 fold increase). However, when we tested MageC2 on p53 activity, we observed 3 fold repression, behavior comparable to that of MageA2 (4,1 fold repression). Western blot analysis showed that p53 protein level was not affected in either case. ARF tumor suppressor is a negative regulator of MAGE-I proteins. While MageA11 is degraded by ARF, MageA2 is relocalized to the nucleoli. To understand the effect of ARF on MageC2, we performed immunofluorescence and protein stabilization assays. No changes in cellular localization were detected when MageC2 was co-transfected with GFP-ARF. Interestingly, ARF expression correlated with 50% decrease of MageC2 protein levels.Our preliminary results suggest that the oncogenic potential MageC2 could rely on its ability to inhibit p53. The mechanism of ARF regulation on MageC2 is more likely to involve protein degradation rather that cellular relocalization.