Comparison of RNA Metabolism in Grarrested and Stimulated Nontransformed and Chemically Transformed Mouse Embryo Cells in Culture1

RNA metabolism and content in AKR-2B cells has been studied extensively in the G0/Gi-arrested state and following the stimulation to proliferate. The purpose of the present study was to examine selected parameters of RNA metabolism in a chemically transformed derivative of the AKR-2B cell, AKRMCA, at a G, arrest point and following the stimulation to undergo DMA synthesis. Flow microfluorometric analysis indi cates that the two cell lines have a comparable degree of growth arrest while autoradiographic data suggest a greater degree of growth arrest for the AKR-MCA cells. There is a similar magnitude of response following growth stimulation. Relative to the resting AKR-2B cells, the transformed AKRMCA cells have higher resting levels of the following: (a) endogenous RNA polymerase II activity; (b) quantity of RNA polymerase II as determined by [3H]amanitin binding; (c) rate of accumulation of poly(A)+ RNA; (d) rate of accumulation of poly(A)~ RNA; and (e) polysome content. Following the stimu lation to proliferate, there is less of an increase in these parameters in the AKR-MCA cells than in the AKR-2B cells so that in late Gì(6 to 8 hr following stimulation) the levels are roughly equivalent in the two cell lines. The MCA cells were found to be insensitive to inhibition of stimulation of DNA synthesis by a-amanitin (an inhibitor of RNA polymerases II and III) and by 5-fluorouridine (an inhibitor of ribosomal RNA proc essing) at the same concentrations which cause complete inhibition of stimulation of DNA synthesis in the AKR-2B cells. In addition, a-amanitin and 5-fluorouridine were found to inhibit stimulation of DNA synthesis in the nontransformed C3H/1 OT'/2 cells but were not inhibitory for the chemically transformed derivative, C3H/MCA-58. These data provide further evidence that the growth-arrested chemically transformed cells are in a different metabolic state and are perhaps at a different arrest point in Gìthan the quiescent nontransformed cells. The alter ations in the chemically transformed cells which render them insensitive to inhibition of DNA synthesis stimulation by two compounds which are specific for inhibition of two separate steps in RNA metabolism remain to be established.