Insights into the relationship between the proteasome and autophagy in human and yeast cells.

In eukaryotes, the ubiquitin-proteasome system (UPS) and autophagy are two major intracellular protein degradation pathways. Several lines of evidence support the emerging concept of a coordinated and complementary relationship between these two processes, and a particularly interesting finding is that the inhibition of the proteasome induces autophagy. Yet, there is limited knowledge of the regulation of the UPS by autophagy. In this study, we show that the disruption of ATG5 and ATG32 genes in yeast cells under both nutrient-deficient conditions as well as stress that causes mitochondrial dysfunction leads to an activation of proteasome. The same scenario occurs after pharmacological inhibition of basal autophagy in cultured human cells. Our findings underline the view that the two processes are interconnected and tend to compensate, to some extent, for each other's functions.