Cyclooxygenase-2 (COX-2) expression is translationally silenced in epithelial cells undergoing radiation-induced apoptosis. CUGBP2, a predominantly nuclear protein, is also rapidly induced in response to radiation and translocates to the cytoplasm. Antisense-mediated suppression of CUGBP2 renders radioprotection through a COX-2-dependent prostaglandin pathway, providing an in vivo demonstration of translation inhibition activity for CUGBP2. CUGBP2 binds to two sets of AU-rich sequences (AREs) located within the first sixty nucleotides of the COX-2 3' untranslated region (3'UTR). Upon binding, CUGBP2 stabilizes a chimeric luciferase-COX-2 3'UTR mRNA but inhibits its translation. These findings identify a novel paradigm for RNA binding proteins in facilitating opposing functions of mRNA stability and translation inhibition and reveal a mechanism for inhibiting COX-2 expression in cancer cells.

This study was negative for the primary end point, but findings for the secondary end points suggest that sargramostim therapy decreased disease severity and improved the quality of life in patients with active Crohn's disease.

Diphenyl difluoroketone (EF24), a molecule having structural similarity to curcumin, was reported to inhibit proliferation of a variety of cancer cells in vitro. However, the efficacy and in vivo mechanism of action of EF24 in gastrointestinal cancer cells have not been investigated. Here, we assessed the in vivo therapeutic effects of EF24 on colon cancer cells. Using hexosaminidase assay, we determined that EF24 inhibits proliferation of HCT-116 and HT-29 colon and AGS gastric adenocarcinoma cells but not of mouse embryo fibroblasts. Furthermore, the cancer cells showed increased levels of activated caspase-3 and increased Bax to Bcl-2 and Bax to Bcl-xL ratios, suggesting that the cells were undergoing apoptosis. At the same time, cell cycle analysis showed that there was an increased number of cells in the G 2 -M phase. To determine the effects of EF24 in vivo, HCT-116 colon cancer xenografts were established in nude mice and EF24 was given i.p. EF24 significantly suppressed the growth of colon cancer tumor xenografts. Immunostaining for CD31 showed that there was a lower number of microvessels in the EF24-treated animals coupled with decreased cyclooxygenase-2, interleukin-8, and vascular endothelial growth factor mRNA and protein expression. Western blot analyses also showed decreased AKT and extracellular signal-regulated kinase activation in the tumors. Taken together, these data suggest that the novel curcumin-related compound EF24 is a potent antitumor agent that induces caspase-mediated apoptosis during mitosis and has significant therapeutic potential for gastrointestinal cancers. [Cancer Res 2008;68(6):1962-9]

RNA-binding proteins play a key role in post-transcriptional regulation of mRNA stability and translation. We have identified that RBM3, a translation regulatory protein, is significantly upregulated in human tumors, including a stage-dependent increase in colorectal tumors. Forced RBM3 overexpression in NIH3T3 mouse fibroblasts and SW480 human colon epithelial cells increases cell proliferation and development of compact multicellular spheroids in soft agar suggesting the ability to induce anchorage-independent growth. In contrast, downregulating RBM3 in HCT116 colon cancer cells with specific siRNA decreases cell growth in culture, which was partially overcome when treated with prostaglandin E 2 , a product of cyclooxygenase (COX)-2 enzyme activity. Knockdown also resulted in the growth arrest of tumor xenografts. We have also identified that RBM3 knockdown increases caspase-mediated apoptosis coupled with nuclear cyclin B1, and phosphorylated Cdc25c, Chk1 and Chk2 kinases, implying that under conditions of RBM3 downregulation, cells undergo mitotic catastrophe. RBM3 enhances COX-2, IL-8 and VEGF mRNA stability and translation. Conversely, RBM3 knockdown results in loss in the translation of these transcripts. These data demonstrate that the RNA stabilizing and translation regulatory protein RBM3 is a novel proto-oncogene that induces transformation when overexpressed and is essential for cells to progress through mitosis.

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