Akt ACTIVITY REGULATES THE UNFOLDED PROTEIN RESPONSE IN CULTURED MAMMALIAN CELLS

MATÍAS BLAUSTEIN; ALFARO J; URRUTIA C; SANCHEZ MANUEL; ALICIA GRANDE; BURKINSHAW B; BERNALES S; ALEJANDRO COLMAN LERNER

Puerto Madryn - Chubut

Congreso; SAIB 46th Annual Meeting Argentine Society for Biochemistry and Molecular Biology XLVI Reunión Anual Sociedad Argentina de Investigación en Bioquímica y Biología Molecular; 2010

Society for Biochemistry and Molecular Biology XLVI Reunión Anual Sociedad Argentina de Investigación en Bioquímica y Biología Molecular

Accumulation of unfolded proteins inside the ER triggers the UPR (Unfolded Protein Response), an homeostatic response involving the activation of three parallel pathways (IRE1, PERK and ATF6), aimed at reducing unfolded protein levels. The UPR promotes cell survival in the short term but stimulates apoptosis if unfolded protein levels remain high. For both pro- and anti-apoptotic functions UPR regulates Akt, the central component of the key mammalian survival pathway, a fraction of which localizes to the ER membrane. Here we study the interconnection between Akt and UPR in 293 and MCF7 cells. To do so, we developed fluorescent protein-based reporters of IRE1, ATF6, Akt1 and Akt2. These reporters allowed us to monitor simultaneously UPR and Akt status in individual cells. Interestingly, blocking Akt phosphorylation with AKT inhibitor IV in unstimulated cells resulted in loss of ER localization of Akt1. Surprisingly, this treatment triggered the UPR, as measured by our ATF6 and IRE1 reporters. Akt localization to the ER seems critical for UPR control, since treatment with the PI3K inhibitor LY294002, which did not alter the ER localization of Akt1, did not activate UPR. We confirmed these results by RT-PCR and western blots. Thus, our evidence indicates that not only can UPR activate Akt but also Akt activity can inhibit UPR, suggesting the operation of complex feedback regulation.