Lysosome exocytosis is required for mitosis

Mitosis, the accurate segregation of duplicated genetic material into what will become two new daughter cells, is accompanied by extensive membrane remodelling and membrane trafficking activities. Early in mitosis, adherent cells partially detach from the substratum, round up and their surface area decreases. This likely results from an endocytic uptake of plasma membrane material. As cells enter cytokinesis they re-adhere, flatten and exhibit an associated increase in surface area. The identity of the membrane donor for this phase of mitosis remains unclear. Here we show by biochemical and imaging approaches that lysosomes undergo exocytosis at telophase and that this requires the activity of phosphatidylinositol 4-kinase-IIIβ. Inhibition of lysosome exocytosis resulted in mitotic failure in a significant proportion of cells suggesting that this facet of lysosome physiology is essential and represents a new regulatory mechanism in mitosis.