A phosphorylation switch regulates RAB6 function during mitosis

Abstract

RAB GTPases are key regulators of membrane trafficking in eukaryotic cells. In addition to their role in interphase, several RAB proteins, including Golgi-associated RAB6, have mitotic functions. The aim of this study was to investigate how the interphasic and mitotic functions of RAB6 could be regulated. Since phosphorylation is a key regulatory process in mitosis, we looked for specific mitotic phosphorylation of RAB6 using a phospho-proteomic approach. We found that RAB6 is phosphorylated at position S52 by the mitotic kinase Pololike kinase 1 (Plk1) in mitosis. Phosphorylated RAB6 localizes at the spindle poles from prophase to anaphase. In metaphase, we observed RAB6A-positive structures containing Mad1 and Mad2 moving along the mitotic spindle via the dynein-dynactin complex. We provide evidence that phosphorylation impairs RAB6A binding to some of its known partners, including p150Glued and Bicaudal-D2. In addition, the overexpression of RAB6A phospho-mutants lead to mitosis and cytokinesis defects. Our results suggest that a cycle of RAB6 phosphorylation/dephosphorylation is required for cell division.