Growth arrest of AKR‐2B cells maintained in the presence of epidermal growth factor or 12‐O‐tetradecanolyhorbol‐13 acetate: Evidence for two separate G1 arrest points

Abstract

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 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, α‐amanitin and 5‐fluorouridine (5‐FU). To determine whether the AKR‐MCA cells growth arrest at a uniue 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 α‐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.