EXPRESSION OF PROLIFERATION-ASSOCIATED ANTIGENS (PCNA, P120, P145) DURING THE REENTRY OF G(0) CELLS INTO THE CELL-CYCLE

Flow cytometric bivariate analysis was used to evaluate the expression of PCNA, p120, and p145 during the G(o) reentry of CHO-K1 cells into the cell cycle. CHO-K1 cells were placed in a G(o)-like state using serum depletion and stimulated to reenter the cell cycle by replating into fresh, serum-containing medium. At discrete intervals after stimulation, replicate samples were stained for either PCNA, p120, or 145; stained for DNA (Coulter DNA-Prep); evaluated on the EPICS Profile I; and analyzed on the EPICS ELITE workstation. PCNA stained less than 10% of the G(o) cells; in contrast, however, 30-35% of the G(o) cells were positive for p120 and p145. Eight hours after stimulating G(o) cells to reenter the cell cycle (during G(o)/G(1)), p120 reached 88% positivity, while p145 and PCNA were 63% and 30% positive, respectively. Cells in S phase (12 and 16 h following G(o) stimulation) were greater than 90% positive for all three antigens. PCNA had the greatest change throughout the G(o) reentry process, both in percentage positive and quantitatively (mean channel fluorescence). This report indicates that all three proliferation-associated antigens studied are differentially expressed during the reentry of G(o) cells into the cell cycle. Furthermore, these antigens may be useful in the early detection of G(o) recruitment. (C) 1994 Wiley-Liss, Inc.