Organelle crosstalk through Rap1 links mitochondria-lysosomes contacts to actin-driven mitochondrial fission

The dynamic morphology of mitochondria relies on dedicated fission and fusion machineries, cytoskeletal remodeling and interorganellar crosstalk. Here we identify Ras-associated protein-1 (RAP1) as a key coordinator of mitochondrial-lysosomal interaction and actin-dependent mitochondrial fission. Genetic ablation of the inner-membrane fusion factor OPA1 in endothelial cells elicited retrograde activation of the RAP1 GTPase pathway. Activated RAP1 localized to mitochondria-lysosome contact sites, where it promoted F-actin polymerization and mitochondrial fragmentation. Inhibition of RAP1 normalized lysosomal positioning and restored elongated mitochondrial network in the absence of OPA1, independently of the canonical fission mediator DRP1. Thus, RAP1 is a previously unrecognized nexus between organelle communication and the actin cytoskeleton, driving mitochondrial division through spatially defined mitochondria-lysosome contacts. These findings establish RAP1 as a central regulator of inter-organelle signaling and highlight a novel layer of control over mitochondrial dynamics.