Impact of HuR inhibition by the small molecule MS-444 on colorectal cancer cell tumorigenesis.

Colorectal cancer (CRC) is the third most common cancer and a leading cause of cancer-related mortality. Observed during CRC tumorigenesis is loss of post-transcriptional regulation of tumor-promoting genes such as COX-2, TNFα and VEGF. Overexpression of the RNA-binding protein HuR (ELAVL1) occurs during colon tumorigenesis and is abnormally present within the cytoplasm, where it post-transcriptionally regulates genes through its interaction with 3'UTR AU-rich elements (AREs). Here, we examine the therapeutic potential of targeting HuR using MS-444, a small molecule HuR inhibitor. Treatment of CRC cells with MS-444 resulted in growth inhibition and increased apoptotic gene expression, while similar treatment doses in non-transformed intestinal cells had no appreciable effects. Mechanistically, MS-444 disrupted HuR cytoplasmic trafficking and released ARE-mRNAs for localization to P-bodies, but did not affect total HuR expression levels. This resulted in MS-444-mediated inhibition of COX-2 and other ARE-mRNA expression levels. Importantly, MS-444 was well tolerated and inhibited xenograft CRC tumor growth through enhanced apoptosis and decreased angiogenesis upon intraperitoneal administration. In vivo treatment of MS-444 inhibited HuR cytoplasmic localization and decreased COX-2 expression in tumors. These findings provide evidence that therapeutic strategies to target HuR in CRC warrant further investigation in an effort to move this approach to the clinic.

Hu antigen R is required for NOX-1 but not NOX-4 regulation by inflammatory stimuli in vascular smooth muscle cells.

OBJECTIVE: NOX-1 and NOX-4 are key enzymes responsible for reactive oxygen species (ROS) generation in vascular smooth muscle cells (VSMC). The RNA-binding protein Hu antigen R (HuR) is implicated in posttranscriptional regulation of gene expression; however, its role regulating NOX is unknown. We investigated transcriptional and posttranscriptional mechanisms underlying angiotensin II (AngII) and IL-1ß regulation of NOX-1 and NOX-4 in VSMC and their implications in cell migration. METHODS: Rat and human VSMC were stimulated with AngII (0.1 µmol/l) and/or IL-1ß (10 ng/ml). NOX-1 and NOX-4 mRNA and protein levels, NOX-1 and NOX-4 promoter and 3'UTR activities, NADPH oxidase activity, ROS production, and cell migration were studied. RESULTS: IL-1ß increased NOX-1 expression, NADPH oxidase activity and ROS production, and decreased NOX-4 expression and H2O2 production in VSMC. AngII potentiated the IL-1ß-mediated induction of NOX-1 expression, NADPH oxidase activity, ROS production, and cell migration. However, AngII did not influence IL-1ß-induced NOX-4 downregulation. AngII + IL-1ß interfered with the decay of NOX-1 mRNA and promoted HuR binding to NOX-1 mRNA. Moreover, HuR blockade reduced NOX-1 mRNA stability and AngII + IL-1ß-induced NOX-1 mRNA levels. IL-1ß decreased NOX-4 expression through a transcriptional mechanism that involved response elements situated in the proximal promoter. AngII and/or IL-1ß-induced cell migration were prevented by NOX-1 and HuR blockade and were augmented by NOX-4 overexpression. CONCLUSION: In VSMC HuR-mediated mRNA stabilization is partially responsible for AngII + IL-1ß-dependent NOX-1 expression, whereas transcriptional mechanisms are involved in decreased NOX-4 expression induced by IL-1ß. NOX4 and HuR regulation of NOX-1 contributes to VSMC migration, important in vascular inflammation and remodeling.