LAUSR

Lysosome function is essential for cellular homeostasis, but quality-control mechanisms that maintain healthy lysosomes remain poorly characterized. Here, we developed a method to measure lysosome turnover and use this to identify a selective mechanism of membrane degradation that involves lipidation of the autophagy protein LC3 onto lysosomal membranes and the formation of intraluminal vesicles through microautophagy. This mechanism is induced in response to metabolic stress resulting from glucose starvation or by treatment with pharmacological agents that induce osmotic stress on lysosomes. Cells lacking ATG5, an essential component of the LC3 lipidation machinery, show reduced ability to regulate lysosome size and degradative capacity in response to activation of this mechanism. These findings identify a selective mechanism of lysosome membrane turnover that is induced by stress and uncover a function for LC3 lipidation in regulating lysosome size and activity through microautophagy.