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. Neuroblastoma (NB),1 a neoplasm that arises from embryonic neural crest tissue, is the second-most common solid pediatric tumor (1). MYCN is amplified in ϳ25% of primary NBs (2-4), and MYCN overexpression is frequently detected in NB tumors (5). Although the clinical significance of MYCN expression in NB tumors that lack MYCN amplification remains controversial (6 -10), a strong correlation between high levels of MYCN expression consequent to genomic amplification of this oncogene and aggressive disease is well established (3-5, 11). Laboratory experiments have further supported an important role for MYCN in determining NB phenotype. Ectopic overexpression of MYCN results in enhanced malignant growth (12, 13), whereas MYCN antisense studies performed by our laboratory and others have shown that down-regulation of MYCN in human NB is associated with a decrease in cellular proliferation and inhibited tumor cell growth in vitro (14 -16). Furthermore, a direct link between MYCN expression and the development of NB has been demonstrated in transgenic mice studies (17).Previously we examined MYCN regulation in N-(neuroblastic, tumorigenic) and S-type (substrate-adherent, non-tumorigenic) subclones (W-N and W-S) of the MYCN-amplified NB cell line NBL-W (18). In addition to distinct morphology and growth characteristics, the subclones have differential levels of MYCN expression despite having the same genomic MYCN copy number. We found that the disparity in steady-state levels of MYCN mRNA in the W-N and W-S cells was largely determined by differences in MYCN mRNA stability (19). Lazarova and co-workers (20) examined MYCN expression in other ...

No abstract

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 monocytedifferentiated 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.

Our studies suggest that TNP-470 treatment may be most effective if it is administered in the setting of microscopic disease. We speculate that TNP-470 may inhibit neuroblastoma growth in children if treatment is initiated following intensive multimodality therapy, when residual disease is minimal.