MageB2 enhances rDNA transcription and global protein synthesis

FRANCO PASCUCCI; LADELFA, FATIMA; MONTE, MARTIN; GASTON AMATO

Congreso; Reunion anual de la SAIC; 2018

MageC2, a MAGE family member, is frequently expressed in a wide range of solid tumors and is associated with a non-favourable clinical course. We recently detected Ras as a potential oncogene that collaborates with MageC2, increasing its stabilty and activity (as repressor of p53 function). Here, we explored two of the main cellular pathways in which the RAS protein operates: the mitogen-activated protein kinases (MAPK) and phosphoinositide-3 kinase (PI3K) pathways and we observed that the main pathway by which Ras stabilizes MageC2 is the MAPK since the ability of activated Ras to enhance transfected Myc-MageC2 protein stability was severely impaired by the MEK inhibitor PD098059, but it was not affected by the Akt inhibitor LY294002. A similar behavior was seen by inhibiting both pathways in human melanoma A375 cells expressing endogenous MageC2. Moreover, transfected Myc-MageC2 stability was strongly increased by activation of endogenous Raf-1 (by Phorbol 12-myristate 13-acetate-PMA treatment, a PKC activator) and transfection with a constitutive active ERK1 also increased Myc-MageC2 stability. To understand if ERK activities lead to MageC2 stabilization, we mutated two highly conserved Ser to Ala on MageC2 (S85 and S86), that are within a consensus phosphorylation sequence for the ERK kinase, and we observed that S85A/S86A MageC2 mutant was still up-regulated after expression of RasV12. Furthermore, we did not observe MageC2/ERK interaction in an immunoprecipitation assay. In order to explore ERK downstream signaling, we inhibited an ERK-activated kinase RSK, but Myc-MageC2 was still stabilized with Ras activation. The mechanism by which the MAPK pathway stabilizes MageC2 is still under study. Our findings have an important biological relevance, since it proposes for the first time that MageC2 tumor protein could act as a link between the activation of the Ras oncogene and the negative regulation of p53, thus enhancing the oncogenic effect of Ras.