The role of 3' poly(A) tail metabolism in tumor necrosis factor-alpha regulation.

In unstimulated RAW 264.7 macrophage-like cells, tumor necrosis factor-alpha (TNF-alpha) mRNA was transcribed and accumulated in the cytoplasm, but the TNF-alpha transcripts failed to associate with polysomes, and TNF-alpha protein was not detected. Stimulation with lipopolysaccharide (LPS) induced an increase in TNF-alpha transcription, cytoplasmic TNF-alpha mRNA accumulation, polysome association, and secretion of TNF-alpha protein. This process was associated with a 200-nucleotide increase in the apparent length of the TNF-alpha mRNA. The difference in TNF-alpha mRNA size was caused by marked truncation of the 3' poly(A) tail in unstimulated cells. Fully adenylated TNF-alpha mRNA appeared within 15 min of LPS stimulation. We speculate that removal of the poly(A) tail blocks initiation of TNF-alpha translation in unstimulated macrophages. LPS inactivates this process, allowing synthesis of translatable polyadenylated TNF-alpha mRNA.