Butyrolactone I induces cyclin B1 and causes G2/M arrest and skipping of mitosis in human prostate cell lines

Several naturally occurring cyclin-dependent kinase (CDK) inhibitors have b een isolated from different lower organisms. In this report, we examined th e effect of one of the CDK inhibitors, butyrolactone I (BL), on the express ion of cyclins D2, A and B1 in three human prostatic cancer cell lines (DU1 45, PC-3, LNCaP) using two colored flow cytometric analysis. The percentage of DU145 cells in the 4C phase of the cell cycle were increased significan tly at both 70 mu M and 100 mu M BL. Furthermore, an additional 8C peak was observed which had double the DNA content of the 4C phase at these concent rations of BL, The appearance of the 8C peak increased gradually and was mo re evident in DU145 and PC-3 than LNCaP. Cells in the 8C peak had either tw o nuclei or abnormal nuclei as observed by Papanicolaou stain. BL also incr eased the amount of cyclin B1 positive cells in the 4C phase. This increase was apparent on day 1 and returned to normal by day 3. Since BL selectivel y inhibits cyclin-dependent kinase, cyclin B1 might accumulate without bein g degraded. Other cyclins were not significantly changed by BL. The data de monstrate that BL inhibited Cdc2 of unsynchronized cultured prostate cancer cells, and interrupted the cell cycle progression toward cell division. Th e BL inhibition of Cdc2 led to the accumulation of cells in the 4C phase wi thout mitosis resulting in an accumulation of cyclin B1. The appearance of cells in the 8C phase may be due to the progression of cells in the 4C phas e through the cell cycle skipping mitosis. Cyclin B1 decreased in correlati on with the progression through a new cell cycle. These results suggest tha t BL does not cause a complete arrest of the cell cycle in G2/M but that BL occasionally allows for the skipping of mitosis and subsequent progression through the cell cycle to occur. (C) 1999 Elsevier Science Ireland Ltd. Al l rights reserved.