Mechanism of growth arrest of chemically transformed cells in culture.

or they growth arrest at subconfluence in serum-deficient medium (17,20).The quiescentcellscanthenbe stimulated to undergo a round of DNA synthesis by adding serum (26, 29) or purified mitogens including EGF3(3, 11, 23), FGF (10), or the tumor promoter, TPA (21, 25). DNA virus transformed cells, on the other hand, do not growth arrest in G, under usual monolayer culture conditions. Theyeither become arrested throughout the cell cycle or continue proliferating until they die even when placed in serum deficient medium (18, 19). However,Holley et a!. (12) have reported that a chemically transformed line of 3T3 cells does become quiescent when grown in medium with 0.2% serum and that these cells growth arrest in the G, phase of the cell cycle. O'Brien and Diamond (16) have shown that chemically transformed hamster cells can be growth ar rested in medium with 10% serum and that the cells can be stimulated to undergo a waveof DNAsynthesis beginning 6 hr following stimulation in a manner similar to that of their nontransformed cells, suggesting that the transformed cells were arrested in G,. The presentstudy was carried out in order to confirm that chemically transformed cells, unlike DNA virus-transformed cells, can become quiescent in G, and to examine the mechanism for growth arrest in the chemically transformed cells. For these studies we have used the nontransformed AKR-2B cell line and a 3-methylcholanthrene-transformed clone (AKR-MCA)derived from the AKR-2B cells (9). In addition, we have examined the C3H/1OT'/2 cell line and a 3-methylcholanthrene-transformed derivative, cabled C3H/ MCA-58 (22). Both chemically transformed cells became quiescent in G1 at a point closer to the onset of DNA synthesis than that for their nontransformed counterparts. The data indicate that the chemically transformed cells growth arrest due to depletion of multiple amino acids and glucose from the chemically defined medium. In contrast to the nontransformed cells, they are unresponsive to serum, EGF,FGF,and TPA.