Peripheral lysosomes recruit PLEKHG3 to focal adhesions and restrain protrusion dynamics.

Lysosomes are dynamic organelles regulating metabolic signaling by recruiting cytosolic molecules to protein platforms on their limiting membrane. We used proximity labeling to define interactors and vicinal proteins of LAMTOR3, a component of the Ragulator scaffold that controls mTORC1 signaling and lysosome positioning. The screen has yielded several previously unappreciated interactors, including an actin remodeling network. Here, we characterize the RhoGEF PLEKHG3 as a LAMTOR3 vicinal protein colocalizing with peripheral lysosomes and cortical F-actin at focal adhesion sites. Forced peripheral dispersion of lysosomes drives PLEKHG3 accumulation at focal adhesions and decreases protrusive activity in both wild-type and PLEKHG3-deficient cells. Thus, lysosome positioning governs both PLEKHG3 localization and protrusive activity, yet the protrusion changes can occur independently of PLEKHG3.