Proteome-wide study of endoplasmic reticulum stress induced by thapsigargin in N2a neuroblastoma cells

► Strong crosstalk between mitochondria and endoplasmic reticulum. ► Upregulated mitochondrial enzymes during endoplasmic reticulum stress. ► Potentially atypical functions of Grp78 in controlling endoplasmic reticulum stress. Disturbances in intraluminal endoplasmic reticulum (ER) Ca2+ concentration leads to the accumulation of unfolded proteins and perturbation of intracellular Ca2+ homeostasis, which has a huge impact on mitochondrial functioning under normal and stress conditions and can trigger cell death. Thapsigargin (TG) is widely used to model cellular ER stress as it is a selective and powerful inhibitor of sarcoplasmic/endoplasmic reticulum Ca2+ ATPases. Here we provide a representative proteome-wide picture of ER stress induced by TG in N2a neuroblastoma cells. Our proteomics study revealed numerous significant protein expression changes in TG-treated N2a cell lysates analysed by two-dimensional electrophoresis followed by mass spectrometric protein identification. The proteomic signature supports the evidence of increased bioenergetic activity of mitochondria as several mitochondrial enzymes with roles in ATP-production, tricarboxylic acid cycle and other mitochondrial metabolic processes were upregulated. In addition, the upregulation of the main ER resident proteins confirmed the onset of ER stress during TG treatment. It has become widely accepted that metabolic activity of mitochondria is induced in the early phases in ER stress, which can trigger mitochondrial collapse and subsequent cell death. Further investigations of this cellular stress response in different neuronal model systems like N2a cells could help to elucidate several neurodegenerative disorders in which ER stress is implicated.