Dimethyl sulfoxide-induced apoptosis in human leukemic U937 cells.

Dimethyl sulfoxide (DMSO), which induces differentiation of myeloid cells, was found to cause apoptosis in human leukemic U937 cells. Apoptosis was assessed by DNA electrophoresis and flow cytometry. The time needed to induce apoptosis varied from a few hours to 2-3 days, depending on the concentration of DMSO used. The plasma membrane remained intact long after DNA fragmentation had occurred. DMSO-induced apoptosis was inhibited by zinc ions and, to a lesser extent, by the protein kinase C activator: phorbol 12-myristate 13-acetate (PMA). Cycloheximide and actinomycin D did not prevent DMSO-induced apoptosis, showing that U937 cells do not require protein or RNA synthesis to undergo apoptosis. DMSO induced apoptosis despite the expression of the anti-apoptotic Bcl-2 protein in U937 cells. The amount of Bcl-2 remained unchanged during DMSO-induced apoptosis.