KIF2β, a new kinesin superfamiIy protein in non-neuronal cells, is associated with lysosomes and may be implicated in their centrifugal translocation

Lysosomes concentrate juxtanuclearly in the region around the microtubule-organizing center by interaction with microtubules, Different experimental and physiological conditions can induce these organelles to move to the cell periphery by a mechanism implying a plus-end-directed microtubule-motor protein (a kinesin-like motor). The responsible kinesin-superfamily protein, however, is unknown. We have identified a new mouse isoform of the kinesin superfamily, KIF2 beta, an alternatively spliced isoform of the known, neuronal kinesin, KIF2, Developmental expression pattern and cell-type analysis in vivo and in vitro reveal that KIF2 beta is abundant at early developmental stages of the hippocampus but is then downregulated in differentiated neuronal cells, and it is mainly or uniquely expressed in non-neuronal cells while KIF2 remains exclusively neuronal, Electron microscopy of mouse fibroblasts and immunofluorescence of KIF2 beta-transiently-transfected fibroblasts show KIF2 and KIF2 beta primarily associated with lysosomes, and this association can be disrupted by detergent treatment. In KIF2 beta-overexpressing cells, lysosomes (labeled with anti-lysosome-associated membrane protein-1) become abnormally large and peripherally located at some distance from their usual perinuclear positions. Overexpression of KIF2 or KIF2 beta does not change the size or distribution of early, late and recycling endosomes nor does overexpression of different kinesin superfamily proteins result in changes in lysosome size or positioning. These results implicate KIF2 beta as a motor responsible for the peripheral translocation of lysosomes.