ZINC DEPRIVATION OF MURINE 3T3 CELLS BY USE OF DIETHYLENETRINITRILOPENTAACETATE IMPAIRS DNA-SYNTHESIS UPON STIMULATION WITH INSULIN-LIKE GROWTH-FACTOR-I (IGF-I)

Growth failure in zinc-deficient animals is associated with decreased DNA synthesis; zinc deprivation of 3T3 cells, by use of diethylenetrin itrilopentaacetate (DTPA), impairs thymidine incorporation when the ce lls are stimulated with fetal bovine serum (FBS). The purpose of this study was to determine the step of cell cycle progression that is affe cted by zinc deprivation. Swiss murine 3T3 cells were cultured for 3 d in complete media and then for 2 d in low serum media. Cells were the n placed in serum-free media and stimulated in sequence with platelet- derived growth factor (PDGF; 3 h), epidermal growth factor (EGF; 0.5 h ) and insulin-like growth factor-I (IGF-I; 16 h). The combination of g rowth factors stimulated thymidine incorporation to the same extent as 10% FBS, and DTPA or EDTA (0.6 mmol/L) inhibited thymidine incorporat ion. Inhibition was prevented by addition of zinc, but not calcium, ir on or cadmium (0.4 mmol/L). When DTPA was present during all stages wi th no addition of zinc, or zinc added during the competency-priming (P DGF and EGF) step, the IGF-I step, or both steps, the zinc effect occu rred at the IGF-I step. Zinc addition 4 h before the measurement of th ymidine incorporation had no ameliorative effect, but the presence of zinc during the prior 12 h increased incorporation. Thus zinc exerts i ts major effect on DNA synthesis during the IGF-I stimulatory phase of the cell cycle. The total zinc concentration of 3T3 cells treated wit h DTPA for 16 h was not different from that of untreated cells; hence only a small compartment of the cell is affected by DTPA.