The mechanisms of endoreduplication

Chinese hamster cells, Don line, were treated with concanavalin A (ConA), calcium ionophore A23187 (A23187), colchicine, sodium fluoride (NaF), 6-thiopurine, dibutyryl cyclic AMP (db-cAMP), and other nucleotides, alone or in combination. A23187 itself did not induce endoreduplication but did so in combination with ConA. NaF could induce endoreduplication and the combination of NaF and ConA showed a synergistic effect. db-cAMP suppressed the inducing activity of ConA. The findings that various chemicals are inducers of endoreduplication and that synergistic effects appear on combined treatments suggest that various mechanisms of induction of endoreduplication may exist. The chemical nature of the inducers and the suppressor, db-cAMP, implies that blocking of the phosphorylation of some cellular components may be involved as a main mechanism. Analysis of the endoreduplication cell cycle indicated that cells treated with reagents in S require a longer cell cycle than those treated in G2 and that the length of the lag period between induction treatment and the initiation of S, the length of S, and the length of G2 war variable. The inducers, induction mechanisms, and the cell cycle of endoreduplication seem to vary; however, the essence of endoreduplication is the omission of mitotic events by connecting S and G1.