ARREST OF CELL-CYCLE PROGRESSION OF HELA-CELLS IN THE EARLY G1 PHASE IN K-DEPLETED CONDITIONS AND ITS RECOVERY UPON ADDITION OF INSULIN ANDLDL()

Cell cycle progression of synchronized HeLa cells was studied by measu ring labeling of the nuclei with [H-3]thymidine. The progression was a rrested in a chemically defined medium in which K+ was replaced by Rb (Rb-CDM) but was restored upon addition of insulin and/or low density lipoprotein (LDL). Cells started DNA synthesis 12 hr after addition o f insulin and/or LDL, regardless of the time of arrest, suggesting the ir arrest early in the G1 phase. After incubation of cells in Rb-CDM c ontaining insulin or LDL singly for 3, 6, or 9 hr, replacement of the medium by that without an addition resulted in marked delay in entry o f cells into the S phase, but in its replacement by medium containing both agents, the delay was insignificant. Synthesis of bulk protein, e stimated as increase in the cell volume, was not strongly inhibited. F rom these results we conclude that cell cycle progression of HeLa cell s in K+-depleted CDM is arrested early in the G1 phase and that the ar rest is due to lack of some protein(s) required for entry into the S p hase that is synthesized in the early G1 phase. (C) 1993 Wiley-Liss, I nc.