Novel phosphorylation of Rab29 that regulates its localization and lysosomal stress response in concert with LRRK2.

Rab proteins are small GTPases that regulate a myriad of intracellular membrane trafficking events. Rab29 is one of the Rab proteins phosphorylated by leucine-rich repeat kinase 2 (LRRK2), a Parkinson's disease-associated kinase. Recent studies suggest that Rab29 regulates LRRK2, whereas the mechanism by which Rab29 is regulated remained unclear. Here we report a novel phosphorylation in Rab29 that is not mediated by LRRK2 and occurs under lysosomal overload stress. Mass spectrometry analysis identified the phosphorylation site of Rab29 as Ser185, and cellular expression studies of phosphomimetic mutants of Rab29 at Ser185 unveiled the involvement of this phosphorylation in counteracting lysosomal enlargement. PKCα and PKCδ were deemed to be involved in this phosphorylation and control the lysosomal localization of Rab29 in concert with LRRK2. These results implicate PKCs in the lysosomal stress response pathway comprised of Rab29 and LRRK2, and further underscore the importance of this pathway in the mechanisms underlying lysosomal homeostasis.