Interplay between PLEKHG3-regulated actin dynamics and lysosomal trafficking in cell motility

Lysosomes are highly dynamic organelles that regulate metabolic signaling pathways by recruiting cytosolic molecules to protein platforms on the lysosomal membrane. We performed a proximity-dependent labeling screen to identify novel proteins recruited to the LAMTOR complex, which regulates lysosome positioning and key signaling pathways such as mTORC1, AMPK, and MEK/ERK. We identified a network of proteins involved in actin remodelling, including Pleckstrin homology domain-containing family G member 3 (PLEKHG3), an actin-binding Rho guanine nucleotide exchange factor enriched in protrusions. We show that GFP-PLEKHG3 accumulates in focal adhesion sites, where it colocalizes with peripheral lysosomes. Peripheral accumulation of lysosomes concentrates PLEKHG3 below the plasma membrane, inhibits protrusion formation and limits cell motility. Thus, subcellular positioning of lysosomes impacts PLEKHG3 subcellular localization and the cells protrusion activity, shape, and motility. The results shed new light on the interplay between lysosomes and actin dynamics and provides insights into the mechanisms controlling cellular processes such as shape regulation and motility of the plasma membrane.