Roles of lysosomal small-molecule transporters in metabolism and signaling

Lysosomes degrade damaged or unwanted cell/tissue components and recycle their building blocks through small-molecule transporters of the lysosomal membrane. They also act as signaling hubs that sense and signal internal cues, such as amino acids, to coordinate cell responses. Recently, the activity of several lysosomal metabolite transporters has been elucidated, bringing new insights into lysosomal functions. Cell biological and structural studies of lysosomal transporters have also highlighted their roles in recruiting signaling complexes to lysosomes and delineated how their substrates gate such hybrid transporter/receptor, or 'transceptor', function. In this review, we summarize recent progress in our understanding of lysosomal transporters, with a focus on the export of lysosomal degradation intermediates, the existence of lysosomal amino acid shuttles that regulate the redox state and pH of the lysosomal lumen, and the role of lysosomal transceptors in nutrient and immune signaling.