The endoplasmic reticulum (ER) is the subcellular compartment where transmembrane and secreted proteins are produced. In normal conditions biosynthesis rate, folding and trafficking of the proteins are tightly regulated through an efficient 'quality control' system. The ER responds to the accumulation of misfolded proteins in its lumen through different signaling pathways known as the unfolded protein response (UPR) [1]. Upon activation, the ER transmembrane protein PERK phosphorylates the alpha subunit of the eukaryotic initiation factor eIF2 [2]. Under these conditions, the transcription factor ATF4 directs the expression of genes involved in resistance to oxidative stress, in amino acid metabolism, as well as the expression of GADD34 (Growth arrest and DNA damage-inducible gene 34) [3]. GADD34 is a regulatory subunit of PP1 phosphatase which dephosphorylates eIF2alpha [4], representing a negative feedback loop of UPR, essential for protein synthesis recovery and cell survival [5].