THE ROLE OF CELL-CYCLE PROGRESSION IN CISPLATIN-INDUCED APOPTOSIS IN CHINESE-HAMSTER OVARY CELLS

Many anticancer drugs arrest cells in G(2) of the cell cycle and subse quently induce cell death by apoptosis. The current experiments establ ish a detailed sequence of events that occur in Chinese hamster ovary CHO/UV41 cells following incubation with cisplatin. Synchronized CHO/U V41 cells were damaged with cisplatin in early S. The cells progressed at a normal rate through S but arrested in G(2). The arrested cells e xhibited normal levels of the mitosis-promoting kinase p34(cdc2) in it s fully phosphorylated, inactive form. After a protracted arrest, the cells dephosphorylated p34(cdc2) and underwent an aberrant mitosis and cytokinesis in which the chromosomes segregated unequally due to the formation of multipolar mitotic spindles. These cells subsequently los t contact with the extracellular matrix, and only then digested their DNA in a manner characteristic of apoptosis. This sequence of events c ould be dramatically accelerated by the addition of caffeine to G(2)-a rrested cells, which induced dephosphorylation of p34(cdc2) and passag e through an aberrant mitosis. It has previously been suggested that p rotein synthesis is required for both caffeine-induced premature mitos is and apoptosis. However, when added in G(2), cycloheximide could inh ibit neither the caffeine-induced mitosis nor apoptosis. Inhibition wa s only seen if cycloheximide was added during S before complete synthe sis of the proteins required for mitosis. These results demonstrate th at, in this model, the proteins thought to be involved in apoptosis ar e those required for normal cell cycle progression. It is hypothesized that the DNA digestion results from loss of signal transduction origi nating from the extracellular matrix but that earlier events leading t o loss of cell adhesion are critical for the induction of apoptosis.