Growth arrest of AKR-2B cells maintained in the presence of epidermal growth factor or 12-O-tetradecanoylphorbol-13 acetate: evidence for two separate G1 arrest points.

Nontransformed mouse embryo derived AKR-2B cells stop growing in the G1 phase of the cell cycle at saturation density due to depletion of serum growth factors, whereas a chemically transformed derivative line (AKR-MCA) arrests growth in G1 at a higher saturation density due to depletion of amino acids and glucose. Stimulation of DNA synthesis is inhibited in the AKR-2B cells, but not in the AKR-MCA cells, by two inhibitors of RNA metabolism, alpha-amanitin and 5-fluorouridine (5-FU). To determine whether the AKR-MCA cells growth arrest at a unique point in G1 or whether they arrest in a physiologic state which can also be achieved by the nontransformed cells, AKR-2B cells were maintained in medium with 10% serum containing the mitogens, epidermal growth factor (EGF) or 12-O-tetradecanoylphorbol-13-acetate (TPA), until they reached saturation density or were arrested at subconfluence by artificial deletion of amino acids from the medium. The AKR-2B cells maintained in EGF or TPA stopped growing in G1 at a higher saturation density, due to depletion of amino acids. Cells arrested in EGF or TPA or in amino acid deficient medium had a shortened interval between stimulation and the onset of DNA synthesis, and the stimulation of DNA synthesis was not inhibited by alpha-amanitin or 5-FU. The data show that the nontransformed AKR-2B cells have two different arrest states which may represent two separate and distinct G1 arrest points--a growth factor deficiency arrest point and a nutrient deficiency arrest point. The nutrient deficiency arrested cells were very similar to the G1 arrested transformed AKR-MCA cells.