Psychosine-triggered endomitosis is modulated by membrane sphingolipids through regulation of phosphoinositide 4,5-bisphosphate production at the cleavage furrow

Endomitosis is a special type of mitosis in which only cytokinesis-the final step of the cell division cycle-is defective, resulting in polyploid cells. Although endomitosis is biologically important, its regulatory aspects remain elusive. Psychosine, a lysogalactosylceramide, prevents proper cytokinesis when supplemented to proliferating cells. Cytokinetic inhibition by psychosine does not inhibit genome duplication. Consequently cells undergo multiple rounds of endomitotic cell cycles, resulting in the formation of giant multiploid cells. Here we successfully quantified psychosine-triggered multiploid cell formation, showing that membrane sphingolipids ratios modulate psychosine-triggered polyploidy in Namalwa cells. Among enzymes that experimentally remodel cellular sphingolipids, overexpression of glucosylceramide synthase to biosynthesize glycosylsphingolipids (GSLs) and neutral sphingomyelinase 2 to hydrolyze sphingomyelin (SM) additively enhanced psychosine-triggered multiploidy; almost all of the cells became polyploid. In the presence of psychosine, Namalwa cells showed attenuated cell surface SM clustering and suppression of phosphatidylinositol 4,5-bisphosphate production at the cleavage furrow, both important processes for cytokinesis. Depending on the sphingolipid balance between GSLs and SM, Namalwa cells could be effectively converted to viable multiploid cells with psychosine.