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 proteins to platforms on their limiting membrane. To identify new proteins recruited to these platforms, we performed a proximity-dependent labelling screen using as bait a component of the late endosomal/lysosomal adaptor and MAPK and mTOR activator (LAMTOR) complex, which regulates lysosome positioning and mTORC1, AMPK and MEK/ERK signaling. We identified a network of proteins involved in actin remodelling, the most prominent of which was Pleckstrin homology domain-containing family G member 3 (PLEKHG3), a Rho guanine nucleotide exchange factors that binds to actin filaments and is 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. This study reveals that the subcellular positioning of lysosomes plays a role in the intracellular distribution of PLEKHG3 and in the cell's protrusion activity, shape, and motility. ### Competing Interest Statement The authors have declared no competing interest.