RELATIVE CONTRIBUTION OF TRANSCRIPTION AND TRANSLATION TO THE INDUCTION OF TUMOR-NECROSIS-FACTOR-ALPHA BY LIPOPOLYSACCHARIDE

The synthesis of tumor necrosis factor-alpha has been suggested to be regulated at both the transcriptional and translational levels in resp onse to stimulation by bacterial lipopolysaccharide, although the rela tive contribution of these two mechanisms has not been quantitatively evaluated. Here, using the murine monocytic cell line RAW 264.7 as a m odel system, we show that steady-state TNF-alpha! mRNA levels increase similar to 77-fold following treatment with lipopolysaccharide for 2 h and to a maximum of 164-fold after 8 h as measured by an RNase prote ction assay. The TNF-alpha gene transcription rate increases similar t o 5-fold following exposure to lipopolysaccharide for 2 h as measured by a nuclear run-on assay. TNF-alpha mRNA stability did not change in the presence of lipopolysaccharide. A ribosomal sedimentation assay an d an RNA transfection assay revealed that the translation rate of endo genous as well as transiently trans fected TNF-alpha mRNAs increases o nly similar to 2-3-fold after stimulation with lipopolysaccharide for 2 h. Taken together, these results suggest that the large increase in the level of secreted TNF-alpha protein in RAW 264.7 cells is due prim arily to activation of TNF-alpha gene transcription.