Tumor specific protein mageB2 regulates ribosomal biogenesis

MONTE M; AMATO GE; LAISECA JE; CASTAÑO BAA; PASCUCCI FA; LADELFA MF

Congreso; LXII Reunión Científica de la Sociedad Argentina de Investigación Clínica (SAIC).; 2017

MageB2 is a tumor specific protein belonging to MAGE family. It confers proliferative advantages to tumoral cells. It is localized in the cytoplasm, nucleus and also in the nucleolus, where the ribosome synthesis takes place. In line with this, immunofluorescence performed in an U2Os cell line inducible for MageB2 expression showed a higher number of nucleolus per cell, suggesting an increase in nucleolar activities due to MageB2 expression. Ribosomal RNA (rRNA) gene expression is linked with cell growth and is compromised in cancer cells. rRNA is synthesized in the nucleoulus as a 47S precursor (pre-rRNA) which is then processed into 18S, 5.8S and 28S rRNA species. We quantified the level of pre-rRNA by RT-qPCR and observed it was higher under MageB2 overexpression conditions. To complement this observation, we generated the HCT116 MageB2 KO cell line, using CRISPR/Cas9 technology. As expected due to MageB2 pro-proliferative role, cell proliferation was affected in the HCT116 MageB2 KO cell line and cell cycle analysis showed a reduction in S phase percentages in comparison with its parental cell line (HCT116 wt). Besides, we observed a reduction in the pre-rRNA levels in the HCT116 MageB2 KO in comparison with HCT116 wt cell line. rRNA precursor is transcript by RNA pol I and controlled by multiple mechanisms. Several activators as UBF and SL1 and repressors as HDACs and DNMTs regulate rRNA transcription to maintain optimal levels of cellular rRNA. In particular, HDAC1 is a known repressor of RNA pol I transcription. By performing immuneprecipitation assays we observed MageB2 strongly interacts with HDAC1. All together, our results suggest MageB2 could modulate ribosomal biogenesis, explaining, at least partially, the basis of its oncogenic potential.