In silico simulation of the palmitate-induced signaling processes and effects of palmitate on PKR phosphorylation. (A) Simulation model. The simulation is based on the systems model that includes the potential interactions and components from the literature, and we further incorporate new observations obtained from experiments to refine the model. The downstream signals emphasized are the level of eIF2α phosphorylation, CREB1 and ATF4 activity. Simulation results based on the network model in Figure 3 is an integration of the current literature knowledge. (B) The difference in the response time of PKR and PERK is added into the model. (C) The knowledge that PP1 activity is unchanged upon palmitate treatment is added into the model. (D) Western blotting analysis. The phosphorylated PKR level was measured using western blotting analysis after 3, 6, 24 hr of palmitate treatment of HepG2 cells. Actin served as a loading control. The level of p-PKR was quantified by normalizing to the levels of total PKR and expressed as the average of three samples ± SD from three independent experiments: **p < 0.01 vs. the control at each time point.