Abstract

Transport Protein Particle (TRAPP) is a multisubunit tethering complex that is involved in membrane trafficking. Lately, there have been numerous cases of proteins with membrane trafficking functions that have been found to have separate functions. These moonlighting functions occur either in a distinct cellular location or during a different phase of the cell cycle. Here we present the unexpected finding that a protein TRAPPC12, a subunit of the mammalian TRAPPIII membrane trafficking complex, plays a role in mitosis. Depletion of TRAPPC12 results in mitotic arrest of the cells. Our results show that TRAPPC12 is hyperphosphorylated early in mitosis and dephosphorylation of TRAPPC12 is necessary for the cell cycle progression. Finally, we demonstrate that a phosphomimetic form of TRAPPC12 leads to an increase in mean mitotic index than does the non-phosphorylatable mutant. Our study identifies a moonlighting function in mitosis for TRAPPC12 that it is regulated by its phosphorylation and dephosphorylation.