Investigating the Role of Pikfyve in Modulating ER Functions/Dynamics and ER-Lysosome Contact Sites

Lysosomes are the major degradative organelle in the cell. Their degradative function is integrated with physiological functions like nutrient sensing, metabolic regulation, and cholesterol transport. The lipid kinase PIKfyve regulates lysosome function. Loss of PIKfyve activity causes several defects including lysosome coalescence. Lysosomes form membrane contact sites (MCSs) with other organelles like the endoplasmic reticulum (ER), which facilitates protein and lipid synthesis. MCSs modulate signalling processes and organelle remodelling. ER-lysosome contacts are implicated in remodelling and repositioning of reticular ER tubules by hitchhiking on lysosomes. We suspect that altered lysosome morphology in PIKfyve-inhibited cells may impact ER structure and dynamics and ER-lysosome contacts. We performed confocal imaging along with proximity ligation assay experiments and observed significant changes in ER morphology and dynamics in PIKfyve-inhibited cells, as well as possible alterations to contact sites between lysosome and ER. Our work suggests that PIKfyve-induced lysosome coalescence disturbs ER morphology and dynamics.