Br-cAMP induction of apoptosis in synchronized CHO cells

The proliferation of suspension cultures of malignant CHO cells was inhibit ed by 0.5 mM Br-cAMP treatment and restored by its removal. This treatment also inhibited histone HI phosphorylation completely reduced histones H2A a nd H4 phosphorylations, induced DNA degradation and produced cells containi ng micronuclei. Agarose gel electrophoresis of the degraded DNA fragments p roduced a "ladder" pattern confirming these cells were undergoing apoptosis . Cell cycle synchrony experiments demonstrated culture growth inhibition w as the result of two different cell cycle-specific processes: [1] arrested cell cycle travel-se at a restriction point in mid-G1, and [2] rapid apopto sis following cell division. Br-cAMP did not stop cells in late-G1, S, G2, or M from traversing the cell cycle and dividing, but. rather, induced apop tosis following mitosis. The restriction point of Br-cAMP arrest was locate d in the middle of a wider band of G1 arrest induced by isoleucine deprivat ion. The cells synchronized in G1 before the restriction point were held in G1-arrest by Br-cAMP and spared apoptotic death. These studies support the further study of cAMP derivatives as agents to induce tumor regression by apoptosis and reverse transformation.