Plasma membrane-to-lysosome FGR signaling regulates endocytosis-associated lysosome homeostasis

Transcriptional control of lysosome biogenesis is an important mechanism underlying cellular adaptation to stress. It is largely unclear how cell surface changes or signals induce alteration in lysosome numbers. By developing a Caenorhabditis elegans-based heterologous TFE3 activation system, we here identify the non-receptor tyrosine kinases SRC-1/-2 (C. elegans) and FGR (mammals) as critical regulators of lysosome biogenesis. In C. elegans, inactivation of src-1/-2 leads to nuclear enrichment of ectopically expressed TFE3 and increased intensity of lysosomal markers. In mammalian cells, FGR inhibition or deficiency similarly results in TFEB/TFE3-dependent lysosomal increase. FGR acts through AKT2 by promoting the activation of the latter. FGR associates with the plasma membrane but is internalized onto endosomes and reaches lysosomes along the endosome-lysosome pathway following endocytosis. Lysosomal FGR promotes AKT2 recruitment to lysosomes, where it phosphorylates TFEB/TFE3 to prevent their activation. Together, these findings reveal a plasma membrane-to-lysosome signaling axis that is required for endocytosis-associated lysosome homeostasis.