High pressure sensitizes murine erythroleukemia cells to caffeine-induced premature mitosis

Murine erythroleukemia (MEL) cells were exposed to a high pressure of 80 MP a or aphidicolin (APH), DNA polymerase inhibitor. The effects of caffeine o n cell cycle were examined using these cells. During the culture of 80 MPa- treated MEL cells at atmospheric pressure, the cells arrested in the G2 pha se, and cyclin B and hyperphosphorylated p34(cdc2) were accumulated. Namely , maturation promoting factor (MPF) composed of p34(cdc2) and cyclin B was inactive. However, upon exposure to caffeine, these cells entered premature ly into mitosis by activating MPF. Caffeine-induced premature mitosis was s uppressed by butyrolactone I and orthovanadate, On the other hand, APH-trea ted MEL cells, which were not exposed to 80 MPa, were not so sensitive to c affeine-induced premature mitosis despite cyclin B accumulation. In this ca se, dephosphorylation of p34(cdc2) was not induced by caffeine. Interesting ly, caffeine-induced premature mitosis in the 80 MPa-treated cells was also suppressed by APH. These results suggest that the premature mitosis of 80 MPa-treated MEL cells by caffeine is induced by active MPF, and that APH-se nsitive molecules such as DNA polymerase may also play an important role in the checkpoint that controls the transition from G2 to M phase.