Tumor protein D52 is expressed at high levels in exocrine cells containing large secretory granules where it regulates Cap-dependent protein secretion however D52 expression is also highly Induced in multiple cancers The present study investigated a role for the Ca2+-dependent phosphorylation of D52 at the single major phospho-acceptor site serine 136 on cell division Ectopic expression of wild type D52 (D52wt) and the phosphomutants serine 136/alanine (S136A) or serine 136/glutamate (S136/E) resulted in significant multinucleation of cells D52wt and S136/E each resulted in a greater than 2-fold increase in multinucleated cells compared to plasmid-transfected controls whereas the S136/A phospho null mutant caused a 9-fold increase in multinucleation at 48 h post-transfection Electron microscopy revealed D52 expression induced a marked accumulation of vesicles along the mid-line between nuclei where the final stages of cell abscission normally occurs Supporting this D52wt strongly colocalized on vesicular structures containing the endosomal regulatory protein vesicle associated membrane protein 8 (VAMP 8) and this colocalization significantly increased with elevations in cellular Ca2+ As VAMP 8 is known to be necessary for the endo-membrane fusion reactions that mediate the final stages of cytokinesis these data indicate that D52 expression and phosphorylation at serine 136 play an important role in supporting the Ca2+-dependent membrane trafficking events necessary for cytokinesis in rapidly proliferating cancer cells (C) 2010 Elsevier Inc All rights reserved