Rab7 deficiency induces lysosome formation from recycling endosomes leading to an increased degradation of cell surface proteins

Abstract

Cell surface receptors such as integrins are repeatedly internalized from and recycled back to the plasma membrane before routed to lysosomes for degradation. In search for modulators of {beta}1 integrin surface stability, we identified the Rab7 small GTPase, believed to be required for lysosome biogenesis, as integrin stabilizer. We show that Rab7 deficiency produces late endosomes and lysosomes with acidic pH, lysosome-specific proteins and membrane architectures that are functional in protein degradation and organelle fusion. Furthermore, Rab7-deficient lysosomes form from Rab4- and transferrin receptor-positive recycling endosomes, resulting in the degradation of proteins designated for recycling. Finally, we also found that overexpression of Rab4 can direct lysosome formation from recycling endosomes in absence as well as presence of Rab7, however, the latter to a much lesser extent. Our findings reveal a lysosome biogenesis and lysosomal protein degradation pathway that becomes dominant in absence of Rab7 or when Rab4 is highly abundant.