Role of tumor specific protein MageB2 in protein translation

ESCALADA, MICAELA; LADELFA, M FÁTIMA; MONTE, MARTÍN; PASCUCCI, FRANCO A.

Congreso; LXIV Reunión Científica de la Sociedad Argentina de Investigación Clínica (SAIC).; 2019

Protein synthesis has a major role in cell proliferation. Many oncogenes affect the translation machinery making aberrant translation a common characteristic of tumor cells. We recently published that expression of the tumor-specific protein MageB2, induces cell proliferation in human cell lines as well as in an experimental mouse model. Our ongoing research showed that endogenous expression of MageB2 enhanced pre-rRNA transcription and ribosome biogenesis. Besides, we also observed a lower rate in protein synthesis in CRISPR/CAS9 MageB2 KO HCT116 cells with respect to WT.Our objective here is to investigate an additional role of MageB2 in protein synthesis regulation, alternative to rRNA transcription regulation, but associated to a functional interaction with the translation machinery and associated pathways.Our first observation obtained from Immunoprecipitation followed by Mass Spectrometry approach was that MageB2 interacts with different ribosomal proteins (RP). We then investigated whether the interaction of MageB2 to RP was linked to its nucleolar localization. Ultracentrifugation in sucrose cushion allowed us to detect MageB2 in cytoplasmic ribosome fraction, together with other RP (S6, S13, L23 and RPLP2). These results suggest that MageB2 could play a role in the nucleolus (rRNA transcription regulation) but also form part of the nascent ribosome that will be involved in protein synthesis as a mature cytoplasmic complex.The eukaryotic Initiation Factor 4E (eIF4E) is a key regulator of protein synthesis, that is activated by phosphorylation and associated to mature ribosomes. We observed a 30% reduction in phospho-eIF4E levels in MageB2 KO cells when compared to WT. This is not due to transcriptional regulation, as quantification by RT-qPCR did not show differences in eIF4E mRNA levels between HCT116 MageB2 KO and WT cell lines.Based on results presented here we propose that MageB2 could form part of tumor cell ribosomes and promote protein synthesis.