V-ATPase-dependent induction of selective autophagy
The general consensus is that the vacuolar-type H+-translocating ATPase (V-ATPase) is critical for macroautophagy/autophagy. However, there is a fundamental conundrum because follicular lymphoma-associated mutations in the V-ATPase result in lysosomal/vacuolar deacidification but elevated autophagy activity under nutrient-replete conditions and the underlying mechanisms remain mysterious. Here, working in yeast, we show that V-ATPase dysfunction activates a selective autophagy flux termed the "V-ATPase-autophagy axis". By combining transcriptomic and proteomic profiling, along with genome-wide suppressor screening approaches, we found that the V-ATPase-autophagy axis is regulated through a unique mechanism distinct from classical nitrogen starvation-induced autophagy. Tryptophan metabolism negatively regulates the V-ATPase-autophagy axis via two parallel effectors. On the one hand, it activates ribosome biogenesis, thus repressing the translation of the transcription factor Gcn4/ATF4. On the other hand, tryptophan fuels NAD+ de novo biosynthesis to inhibit autophagy. These results provide a clear explanation for the mutational activation of autophagy seen in follicular lymphoma patients. Overall design: Trpytophan prototrophic and tryptophan auxotrophic yeast SEY6210 cells are cultured in nutrient-rich YPD medium, then treated with/without 3-IAA to induce temporal degradation of VMA2-AID*-9MYC protein.