miR-519 suppresses tumor growth by reducing HuR levels.

The RNA-binding protein HuR is highly abundant in many cancers. HuR expression was recently found to be repressed by microRNA miR-519, which potently lowered HuR translation without influencing HuR mRNA abundance. Here, we examined the levels of HuR and miR-519 in pairs of cancer and adjacent healthy tissues from ovary, lung, and kidney. In the three sample collections, the cancer specimens showed dramatically higher HuR levels, unchanged HuR mRNA concentrations, and markedly reduced miR-519 levels, when compared with healthy tissues. As tested using human cervical carcinoma cells, miR-519 reduced tumorigenesis in athymic mice. Compared with the tumors arising from control cells, cells overexpressing miR-519 formed significantly smaller tumors, while cells expressing reduced miR-519 levels gave rise to substantially larger tumors. Evidence that the miR-519-elicited reduction of HuR was critical for its tumor suppressor influence was obtained by reducing HuR, as HuR-silenced cells formed markedly smaller tumors and were unable to form large tumors even after lowering miR-519 abundance. Together, our data reveal that miR-519 inhibits tumorigenesis in large part by repressing HuR expression.

The mRNA-destabilizing protein tristetraprolin is suppressed in many cancers, altering tumorigenic phenotypes and patient prognosis.

AU-rich element-binding proteins (ARE-BP) regulate the stability and/or translational efficiency of mRNAs containing cognate binding sites. Many targeted transcripts encode factors that control processes such as cell division, apoptosis, and angiogenesis, suggesting that dysregulated ARE-BP expression could dramatically influence oncogenic phenotypes. Using several approaches, we evaluated the expression of four well-characterized ARE-BPs across a variety of human neoplastic syndromes. AUF1, TIA-1, and HuR mRNAs were not systematically dysregulated in cancers; however, tristetraprolin mRNA levels were significantly decreased across many tumor types, including advanced cancers of the breast and prostate. Restoring tristetraprolin expression in an aggressive tumor cell line suppressed three key tumorgenic phenotypes: cell proliferation, resistance to proapoptotic stimuli, and expression of vascular endothelial growth factor mRNA. However, the cellular consequences of tristetraprolin expression varied across different cell models. Analyses of gene array data sets revealed that suppression of tristetraprolin expression is a negative prognostic indicator in breast cancer, because patients with low tumor tristetraprolin mRNA levels were more likely to present increased pathologic tumor grade, vascular endothelial growth factor expression, and mortality from recurrent disease. Collectively, these data establish that tristetraprolin expression is frequently suppressed in human cancers, which in turn can alter tumorigenic phenotypes that influence patient outcomes.