Quercetin arrests human leukemic T-cells in late G1 phase of the cell cycle

The effect of quercetin, a flavonoid found in many plants, on the proliferation of human leukemic T-cells was analyzed. Quercetin reversibly blocked the cell cycle at a point 3-6 h before the start of DNA synthesis. Expression of the growth-related genes histone H4, cyclin A and B, and p34cdc2 was suppressed in cells blocked with quercetin. Comparison of the quercetin arrest points with those of the cell cycle inhibitors aphidicolin and mimosine revealed a temporal order of arrest points in G1 of quercetin, mimosine, and aphidicolin. Mimosine and aphidicolin did not inhibit the expression of cyclin A or p34cdc2, whereas all three reagents inhibited expression of cyclin B. Low concentrations of the protein inhibitor cycloheximide inhibited release of the quercetin but not the mimosine or aphidicolin block. A [35S]methionine-labeled M(r) 60,000 protein disappeared in quercetin-treated cells and was rapidly synthesized after removal of quercetin, suggesting the possibility that the M(r) 60,000 protein induces DNA synthesis after the cell is released from a quercetin block. These results suggest the usefulness of quercetin in studies of the regulation of late G1 phase.