Seminar by Pr Agnieszka CHACINSKA Centre of New Technologies, University of Warsaw, Pologne

Reporting on the status of mitochondria

Mitochondria must import the large majority of their proteome. We aim to understand cellular consequences of defects in the mitochondrial protein import. Two main arms of the cellular response to protein import dysfunction include the inhibition of cytosolic translation and activation of the major protein degradation machinery, the proteasome. The stimulation of the proteasome is driven by its more efficient assembly as a direct response to the amount of mistargeted proteins. The mechanism is beneficial for cells. Interestingly, activation of the proteasome could be uncoupled from translational inhibition by mistargeting of mitochondrial proteins and in the presence of healthy mitochondria. Under these conditions only proteasomal activity, and not the cellular protein synthesis, was modulated. The synthesis of cellular proteins is regulated by the signals, which come directly from the dysfunctional mitochondria. To understand translational inhibition, we performed a global, quantitative, and site-specific redox proteomic analysis to delineate the yeast redoxome. Increased levels of intracellular ROS caused by the mitochondria serve as a signal to attenuate global protein synthesis. Mapping of redox-active thiols in proteins revealed ROS-sensitive sites in several components of the translation apparatus. We demonstrate that increased levels of intracellular ROS caused by dysfunctional mitochondria serve as a signal to attenuate global protein synthesis. Hence, we propose a universal mechanism that controls protein synthesis by inducing oxidative changes in the translation machinery