OBJECTIVETo confirm the unscheduled in vivo and in vitro expression models of cyclin B1 in cancer cells so as to study the different profiles of cyclin B1 in G(1)-phase immortal cells under different culture states and culture conditions.

METHODSMultiparameter flow cytometry (FCM) was used to correlate the expression of cyclin B1 with the position in cell cycle of immortal cells in vivo and in vitro using the MOLT-4 cell line as control. Cells which belonged to G(1)-phase were sorted by FCM according DNA diploidy, and then the expression of cyclin B1 was examined by confocal microscope to confirm the results. For further analysis, different subgroups in G(1) phase were sorted according to the fluorescent intensity of cyclin E, and then the exact period in G(1) phase when cyclin B1 was expressed, were assayed by Western blot.

RESULTSUnscheduled expression of cyclin B1 expressed in G(1)-phase was found not only in synchronized leukemia cells MOLT-4 and in vivo transformed T-7 cells, but also in vivo tumor cells detached from clinical samples. In the synchronized growing cells, cyclin B1 was mainly detected in the early G(1) phase, while in transformed T7 cells, cyclin B1 was mainly detected in the late G(1) phase.

CONCLUSIONThe limitation of detecting cyclin B1 is due to its unscheduled expression, rending cyclin B1 being detected at different time-spots in the G(1) phase. This phenomenon may be related to the adjustment between the loss of control in cell proliferation and cell apoptosis, thereby leading to tumorigenesis.