TUMOR SPECIFIC PROTEIN MAGEB2 REGULATES RIBOSOMAL BIOGENESIS

LADELFA, MARÍA F.; PASCUCCI, FRANCO A.; AMATO, GASTON E.; MONTE, MARTIN; CASTAÑO, BRYAN A.; LAISECA, JULIETA E.

Buenos Aires

Congreso; Reunion Conjunta de Sociedades de Biociencias; 2017

MageB2 is a tumor specific protein belonging to MAGEfamily. Previously, we reported MageB2 confers proliferative advantages totumoral cells and localized in the cytoplasm, nucleus and also in thenucleolus, where the ribosome synthesis takes place. Here we study therelationship between MageB2 and the ribosomal biogenesis. In line with its nucleolarlocalization, immunofluorescence performed in an U2Os cell line inducible forMageB2 expression showed a higher number of nucleolus per cell (5.69 in controlvs 6.93 in MageB2 expressing cells), suggesting an increase in nucleolaractivities due to MageB2 expression. Ribosomal RNA (rRNA) gene expression islinked with cell growth and compromised in cancer cells. rRNA is synthesized inthe nucleolus as a 47S precursor (pre-rRNA). We quantified the level of pre-rRNAby RT-qPCR and observed it was higher under MageB2 overexpression conditions. Tocomplement this observation, we generated the HCT116 MageB2 KO cell line, usingCRISPR/Cas9 technology. As expected due to MageB2 pro-proliferative role, cellproliferation was affected in the HCT116 MageB2 KO cell line and cell cycleanalysis performed by flow cytometry showed a reduction in S phase percentagesin comparison with its parental cell line (8.63% in HCT116 wt vs 4.02% inHCT116 MageB2 KO). Besides, we observed a 30% reduction in the pre-rRNA levelsin the HCT116 MageB2 KO in comparison with HCT116 wt cell line.   rRNA precursor is transcribed by RNA pol I andcontrolled by multiple mechanisms. Activators as UBF and SL1 and repressors asHDACs and DNMTs regulate rRNA transcription to maintain optimal levels ofcellular rRNA. In particular, HDAC1 is a known repressor of RNA pol Itranscription. By performing immuneprecipitation assays we observed MageB2strongly interacts with HDAC1. All together, our results suggest MageB2 couldmodulate ribosomal biogenesis, explaining, at least partially, the basis of itproliferative potential.