The Effect of Actinomycin D and 5-Azacytidine on Macromolecular Synthesis in Murine Myeloma Tumor Cells

Abstract

Abstract A tissue culture-adapted cell line of the murine myeloma tumor MOPC 21 was employed to study the relationship between RNA and protein synthesis in myeloma tumor cells. This cell line constitutively synthesizes and secretes a large proportion of its total cellular protein as a homogeneous γG immunoglobulin. Two inhibitors which function at the level of transcription, actinomycin D and 5-azacytidine, were used to obtain an estimate for the half-life of the mRNA coding for myeloma globulin. While a high concentration of actinomycin D (5.0 µg/ml) inhibited RNA synthesis by greater than 95% after one hr of incubation, a high concentration of 5-azacytidine (100 µg/ml) allowed considerable RNA synthesis for 4 hr. The half-life of the myeloma mRNA, as estimated by measuring the capacity to synthesize and secrete myeloma globulin while transcription of functional mRNA was inhibited, appeared to be of the order of 2 to 3 hr. The average half-life of the mRNA coding for total intracellular protein appeared to be similar to that of the globulin mRNA by these methods. The protein secreted in the presence of both actinomycin D and 5-azacytidine was in the form of a reduced amount of intact γG globulin. Neither inhibitor showed a nonspecific effect on incorporation in a cell-free protein-synthesizing system. The implications of a relatively short-lived mRNA coding for myeloma globulin are discussed.