12 research outputs found
Folliculin directs the formation of a Rab34âRILP complex to control the nutrientâdependent dynamic distribution of lysosomes
The spatial distribution of lysosomes is important for their function and is, in part, controlled by cellular nutrient status. Here, we show that the lysosome associated BirtâHogeâDubĂ© (BHD) syndrome renal tumour suppressor folliculin (FLCN) regulates this process. FLCN promotes the periânuclear clustering of lysosomes following serum and amino acid withdrawal and is supported by the predominantly Golgiâassociated small GTPase Rab34. Rab34âpositive periânuclear membranes contact lysosomes and cause a reduction in lysosome motility and knockdown of FLCN inhibits Rab34âinduced periânuclear lysosome clustering. FLCN interacts directly via its Câterminal DENN domain with the Rab34 effector RILP. Using purified recombinant proteins, we show that the FLCNâDENN domain does not act as a GEF for Rab34, but rather, loads active Rab34 onto RILP. We propose a model whereby starvationâinduced FLCN association with lysosomes drives the formation of contact sites between lysosomes and Rab34âpositive periânuclear membranes that restrict lysosome motility and thus promote their retention in this region of the cell
Vac14 protein multimerization is a prerequisite step for Fab1 protein complex assembly and function
Phosphatidylinositol 3,5-bisphosphate (PtdIns(3,5)P2) helps control various endolysosome functions including organelle morphology, membrane recycling, and ion transport. Further highlighting its importance, PtdIns(3,5)P2 misregulation leads to the development of neurodegenerative diseases like Charcot-Marie-Tooth disease. The Fab1/PIKfyve lipid kinase phosphorylates PtdIns(3)P into PtdIns(3,5)P2 whereas the Fig4/Sac3 lipid phosphatase antagonizes this reaction. Interestingly, Fab1 and Fig4 form a common protein complex that coordinates synthesis and degradation of PtdIns(3,5)P2 by a poorly understood process. Assembly of the Fab1 complex requires Vac14/ArPIKfyve, a multimeric scaffolding adaptor protein that coordinates synthesis and turnover of PtdIns(3,5)P2. However, the properties and function of Vac14 multimerization remain mostly uncharacterized. Here we identify several conserved C-terminal motifs on Vac14 required for self-interaction and provide evidence that Vac14 likely forms a dimer. We also show that monomeric Vac14 mutants do not support interaction with Fab1 or Fig4, suggesting that Vac14 multimerization is likely the first molecular event in the assembly of the Fab1 complex. Finally, we show that cells expressing monomeric Vac14 mutants have enlarged vacuoles that do not fragment after hyperosmotic shock, which indicates that PtdIns(3,5)P2 levels are greatly abated. Therefore, our observations support an essential role for the Vac14 homocomplex in controlling PtdIns(3,5)P2 levels.
 </p