Interleukin-11 mRNA Stabilization in Phorbol Ester-Stimulated Primate Bone Marrow Stromal Cells

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Abstract
12-O-Tetradecanoylphorbol-13-acetate (TPA) stimulation of PU-34 cells, a primate bone marrow stromal cell line, resulted in a prolonged elevation of interleukin-11 (IL-11) mRNA, which can be inhibited by protein synthesis inhibitors. Nuclear run-on assays and actinomycin D experiments demonstrated that the up-regulation of IL-11 gene expression is mainly controlled at the posttranscriptional level through the protein kinase C (PKC) pathway. Inhibition of PKC activity by calphostin C generated an IL-11 mRNA degradation intermediate in TPA-stimulated PU-34 cells. This intermediate retains the 5' untranslated region (5'UTR) and coding region of the IL-11 mRNA but has lost the poly(A) tail and the 3'UTR. The mechanisms underlying IL-11 mRNA stabilization were further investigated by transfections with a variety of chimeric IL-11 constructs and deletion mutants. Two important observations were made from these transient expression experiments: (i) the same 3'UTR of IL-11 mRNA shown to confer instability in one chimeric transcript may not function as a destabilizer in another chimeric RNA, and (ii) the 5'UTR, coding region, and 3'UTR all contribute to IL-11 mRNA decay, and labile IL-11 deletion transcripts are not necessarily stabilized by TPA stimulation. Our study suggests that multiple regions within the IL-11 mRNA are involved in TPA-stimulated IL-11 mRNA stabilization, possibly through a unique RNA folding conformation involving interactions of various RNA sequences within the IL-11 mRNA molecule.