INTERLEUKIN-11 MESSENGER-RNA STABILIZATION IN PHORBOL ESTER-STIMULATED PRIMATE BONE-MARROW STROMAL CELLS

12-O-Tetradecanoylphorbol-13-acetate (TPA) stimulation of PU-34,cells, a primate hone marrow stromal cell line, resulted in a prolonged elev ation of interleukin-11 (IL-11)-mRNA, which can be inhibited by protei n synthesis inhibitors, Nuclear run-on assays and actinomycin D experi ments 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 PRC activity by calphostin C ge nerated an IL-11 mRNA degradation intermediate in TPA-stimulated PU-34 cells. This intermediate retains the 5' untranslated region (5'UTR) a nd coding region of the IL-11 mRNA but has lost the poly(A) tail add t he 3'UTR. The mechanisms underlying IL-11 mRNA stabilization were furt her investigated by transfections with a variety of chimeric IL-11 con structs and deletion mutants, Two important observations were made fro m these transient expression experiments: (i) the same 3'UTR of IL-11 mRNA shown to confer instability in one chimeric transcript may not fu nction 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 labil e IL-11 deletion transcripts are not necessarily stabilized by TPA sti mulation, Our study suggests that multiple regions within the IL-11 mR NA are involved in TPA-stimulated IL-11 mRNA stabilization, possibly t hrough a unique RNA folding conformation involving interactions of var ious RNA sequences within the IL-11 mRNA molecule.