Rheumatoid arthritis synovial fluid macrophages express decreased tumor necrosis factor-related apoptosis-inducing ligand R2 and increased decoy receptor tumor necrosis factor-related apoptosis-inducing ligand R3.

OBJECTIVE: To characterize the expression pattern of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and its cognate receptors (TRAIL R1, R2, R3, and R4) on rheumatoid arthritis (RA) synovial fluid (SF) lymphocytes and monocyte/macrophages and on cultured RA synovial fibroblasts. METHODS: The expression of TRAIL and TRAIL receptors on RA SF lymphocytes and monocyte/macrophages, normal macrophages, and RA synovial fibroblasts was examined by flow cytometry with previously characterized monoclonal antibodies. The ability of adenoviral-mediated delivery of TRAIL to induce macrophage or RA synovial fibroblast apoptosis was examined by flow cytometry. RESULTS: By flow cytometry, neither TRAIL nor its cognate receptors was detectable on RA SF lymphocytes or RA synovial fibroblasts. In contrast, RA SF macrophages expressed TRAIL R3, a decoy receptor (P < 0.01 versus isotype control), but not TRAIL, or TRAIL R1, R2, or R4. Normal peripheral blood-derived monocyte-differentiated macrophages expressed TRAIL R2 (P < 0.01), but not TRAIL or the other TRAIL receptors. Adenoviral-mediated delivery of TRAIL had no effect on the survival of normal macrophages or RA synovial fibroblasts but readily induced apoptosis in the prostate cancer cell line (PC-3) that expressed TRAIL R1 and R2. CONCLUSION: TRAIL R1 and R2, which are required for signal transmission by TRAIL, were not detected on RA SF lymphocytes, macrophages, or synovial fibroblasts. These observations do not support a potential therapeutic role for TRAIL in RA.

HuD, a neuronal-specific RNA-binding protein, increases the in vivo stability of MYCN RNA.

MYCN amplification and consequent deregulated expression plays a crucial role in determining the clinical behavior of neuroblastoma. Enhanced expression of MYCN confers growth potential to neuroblastoma cells, and a direct link between MYCN expression and the development of neuroblastoma has been demonstrated in transgenic mice studies. Although the molecular pathways underlying the regulation of MYCN have not been fully elucidated, post-transcriptional mechanisms appear to be important. Previously, we reported that an embryonic lethal abnormal vision-like (ELAV) protein binds with high specificity to at least two AU-rich elements within the MYCN 3'-untranslated region. In this study, we characterized the ability of cis-acting elements within the MYCN 3'-untranslated region to destabilize mRNA in cells and examined the functional consequences of its interactions with the ELAV protein HuD. We show that at least 4 cis-acting elements within the MYCN 3'-untranslated region are able to signal the degradation of stable heterologous mRNA. Ectopic overexpression of HuD dramatically inhibits RNA decay mediated by the full-length MYCN 3'-untranslated region and cis-acting destabilizing elements that harbor HuD binding sites in vivo. HuD may contribute to the malignant phenotype of neuroblastoma cells by stabilizing MYCN mRNA, thereby enhancing steady-state levels of expression of this oncogene.