Arf1-PI4KIII positive vesicles regulate PI(3)P signaling to facilitate lysosomal tubule fission

Boutry et al. show that Arf1-PI4KIII & beta; positive vesicles participate in the fission of lysosomal tubules through lysosomal PI(3)P regulation. This work identifies new components involved in the scission of lysosomal tubules and demonstrates that this process requires an exquisite regulation of phosphoinositides on lysosomes. Formation and fission of tubules from autolysosomes, endolysosomes, or phagolysosomes are required for lysosome reformation. However, the mechanisms governing these processes in these different lysosomal organelles are poorly understood. Thus, the role of phosphatidylinositol-4-phosphate (PI(4)P) is unclear as it was shown to promote the formation of tubules from phagolysosomes but was proposed to inhibit tubule formation on autolysosomes because the loss of PI4KIII & beta; causes extensive lysosomal tubulation. Using super-resolution live-cell imaging, we show that Arf1-PI4KIII & beta; positive vesicles are recruited to tubule fission sites from autolysosomes, endolysosomes, and phagolysosomes. Moreover, we show that PI(4)P is required to form autolysosomal tubules and that increased lysosomal tubulation caused by loss of PI4KIII & beta; represents impaired tubule fission. At the site of fission, we propose that Arf1-PI4KIII & beta; positive vesicles mediate a PI(3)P signal on lysosomes in a process requiring the lipid transfer protein SEC14L2. Our findings indicate that Arf1-PI4KIII & beta; positive vesicles and their regulation of PI(3)P are critical components of the lysosomal tubule fission machinery.