Prostaglandins E1 and E2 interact with prostaglandin F2alpha to regulate initiation of DNA replication and cell division in swiss 3T3 cells.

Prostaglandin (PG) E1 or E2 added at 2-1,000 ng/ml to quiescent cultures of Swiss 3T3 cells synergistically enhanced the rate of initiation of DNA replication stimulated by PGF2 alpha alone or with insulin. Neither PGD2 nor PGF1 alpha had any effect with PGF2 alpha. An increase in the rate of entry into S phase also occurred when PGE1 or PGE2 was added 8 or 15 hr after addition of PGF2 alpha. However, adding PGE1 and PGE2 together with PGF2 alpha did not further enhance the synergistic effect observed with PGE1 or PGE2 separately. The synergistic effect was also observed in stimulation of 2-deoxyglucose uptake but not in early changes of intracellular levels of cAMP. These results may be relevant in understanding the control of fibroblastic proliferation in wound healing and may provide an alternative mechanism for oncogenic transformation.

Epidermal growth factor initiates DNA synthesis after a time-dependent sequence of regulatory events in Swiss 3T3 cells--interactions with hormones and growth factors.

Epidermal growth factor (EGF) stimulates the initiation of DNA synthesis in Swiss 3T3 cells after a constant prereplicative period of 14-15 hours. The final rate of initiation follows apparent first-order kinetics and can thus be quantified by a rate constant k. The value of k can be changed by later additions during the prereplicative period: When cells stimulated by a very low concentration of EGF, alone or with insulin, which results in a relatively low value of k, receive a saturating amount of EGF at 15 hours, then k is markedly increased after 4-6 hours. Insulin alone (up to 200 ng/ml) is unable to set the lag phase, but does have a synergistic effect on the value of k given by EGF. When added at 15 hours, insulin also increases K, but after a delay of 4-6 hours. In contrast, both hydrocortisone and prostaglandin E1 (PGE1) inhibit the stimulation of DNA synthesis by EGF only during the first 8 hours of the prereplicative period of decreasing the value of k. Prostaglandin F2 alpha), which stimulates DNA synthesis in a similar mode as EGF, when added with EGF has a synergistic effect on DNA synthesis. This suggests that EGF and PGF2 alpha, nevertheless, act through different regulatory events.

Microtubule-disrupting agents affect two different events regulating the initiation of DNA synthesis in Swiss 3T3 cells.

The stimulatory effect of epidermal growth factor, alone or with insulin, on the rate of initiation of DNA synthesis in Swiss 3T3 cells can be synergistically enhanced by the addition of either Colcemid or colchicine at 1 microM. However, both Colcemid and colchicine can exert the synergistic effect only when added earlier than 8 hr of the prereplicative period (lag phase). Removal of Colcemid (which allows for rapid reassembly of microtubules) earlier than 10 hr of the lag phase results in a loss of the synergistic effect. This suggests that microtubules must remain disrupted for longer times to accomplish some putative event(s) necessary for increasing the rate of initiation of DNA synthesis. Preincubation of quiescent cells with either Colcemid or colchicine for 8 hr prior to adding epidermal growth factor, alone or with insulin, shortens the lag phase by about 4 hr, irrespective of the resulting rate of initiation of DNA synthesis. These results suggest that the state of microtubules is affecting independently at least two different events involved in regulating time initiation of DNA synthesis.