Early cellular responses to diverse growth stimuli independent of protein and RNA synthesis

Serum, elevated pH, excess Zn++, 9,10 dimethyl-1,2 dibenzanthracene (DMBA) and insulin accelerate the progress of growth-inhibited chick embryo cells into the S-period of DNA synthesis. A comparative study was made of their capacity to elicit other cellular responses within two hours after their application. All the agents studied stimulated the uptake of the glucose analogue 2-deoxy-D-glucose (2-dGlc). Elevated pH elicited a more striking increase than the other agents in the uptake of the amino acid analogue alpha-amino isobutyric acid (AIB). The application of subtoxic concentrations of Zn++ or DMBA did not stimulate the uptake of uridine by cells nor its incorporation into RNA when tested at 2 hours. However, it was found that the stimulation of uridine utilization did occur but was delayed several hours. Similarly, the accelerated onset of DNA synthesis was also delayed for several hours by these agents. Insulin acted like serum in stimulating the utilization of 2-dGlc, AIB and uridine. Serum and DMBA were particularly effective in stimulating the utilization of choline. It was concluded that the utilization of 2-dGlc, uridine and thymidine are affected similarly by all the agents, but that there may be differential effects in the utilization of AIB and choline. The inhibition of RNA synthesis by actinomycin D did not prevent the relative stimulation of 2-dGlc, AIB and choline utilization by serum and pH treatment. The inhibition of protein synthesis by cycloheximide did not prevent the relative stimulation of 2-dGlc and choline utilization by serum and pH treatment. It partially blocked the increased uptake of AIB and had erratic effects on the utilization of uridine. It was concluded that neither RNA nor protein synthesis is required for some, if not all, the early responses to growth stimuli measured here. The inhibited cell appears to be a poised system which carries out a programmed array of reactions characteristic of the cell type following perturbation by a variety of unrelated agents. In vivo specificity is provided by the physiological reagents available (i.e., hormones) and their capacity to interact with different cell types.