Mechanism of killing Chinese hamster ovary cells heated in G1: effects on DNA synthesis and blocking in G2.
To determine where in the cell cycle Chinese hamster ovary cells die following heating in G1, a mild hyperthermia treatment, i.e., 10 or 11.5 min at 45.5 degrees C, resulting in 40-50% cell kill was used. After a 7-14-h delay in G1, the cells heated in G1 eventually entered S phase and replicated all their DNA. Both an autoradiographic analysis with tritiated thymidine and a bromodeoxyuridine-propidium iodide bivariate analysis by flow cytometry revealed that both clonogenic and nonclonogenic cells were delayed in progression through S phase for at least 4 h. Then they completed replication of all their DNA and entered G2. Alkaline sucrose gradient sedimentation analysis revealed that these heated cells could complete replicon elongation into cluster-sized molecules of 120-160 S which persisted for 2-12 h after heating. However, further replicon elongation into multicluster-sized molecules greater than 160 S required an additional 12 h in heated cells compared to the 4 h needed in unheated control cells. Our results when compared with the literature suggest that when G1 cells are heated to a survival level of about 50%, the nonclonogenic cells recover from a long delay in G1, traverse S at a reduced rate, and then die either in G2 or as multinucleated cells after an aberrant division.
Wong
R S
RS
Radiation Oncology Research Laboratory, University of California, San Francisco 94143.
Borrelli
M J
MJ
Thompson
L L
LL
Dewey
W C
WC
D000818:Animals; D002460:Cell Line; D002470:Cell Survival; D006224:Cricetinae; D004247:DNA / Q000096:biosynthesis*; D006358:Hot Temperature / Q000009:adverse effects*; D066298:In Vitro Techniques; D007399:Interphase; D013997:Time Factors
D004247:DNA