Posttranscriptional Regulation Of IL-10 And IFN-? Expression By MicroRNA

Part I microRNA-4661 up-regulates IL-10 expression in TLR-triggered macrophages by antagonizing RNA-binding protein tristetraprolin-mediated IL-10 mRNA degradationmicroRNAs are generally accepted to regulate gene expression posttranscriptionally by inhibiting translation or inducing target mRNA degradation. However, new mechanisms for miRNAs to regulate gene expression in other manners also attract much attention. More and more novel microRNAs (miRNAs) are discovered by the advanced sequencing technology, but their biological functions are largely unknown. Up to now, the function of miR-4661, a miRNA discovered in mouse embryonic stem (ES) cells, remains unclear. Here we report that miR-4661 can up-regulate both mRNA and protein expression of interleukin (IL)-10 in TLR-triggered macrophages. Further experiments show that miR-4661 can competitively bind to the IL-10 3'UTR AU-rich elements (ARE), which is a characteristic binding site of RNA-binding protein (RBP). Tristetraprolin (TTP) is a well known RBP, mediating rapid degradation of IL-10 mRNA. miRNA always mediates target mRNA degradation or translation repression modestly, thus the net effect of miR-4661's binding to IL-10 ARE is to prevent IL-10 mRNA degradation mediated by TTP, finally extending IL-10 mRNA half-life and resulting in the up-regulation of IL-10 expression. So, competitive blockade of RBP to bind same target mRNA and subsequent stabilization of target mRNA is an alternative mechanism for gene regulation by miRNAs. Also, a new way for regulation of IL-10 by miRNAs is outlined.Part?miR-29 controls innate and adaptive immune responses against intracellular bacterial infection by targeting IFN-?miRNAs have been identified as important regulators of numerous biological systems, including mammalian immune system. It has been shown that miRNAs have unique expression profiles in cells of the innate and adaptive immune systems and have pivotal roles in the regulation of development and function of the immune cells. For T cells, the expression profile has identified a broad range of expressed miRNA species, and the expression patterns of miRNAs vary between different T cell subsets and stages of development, indicating that the unique expression patterns of miRNAs may contribute to the identity of the cell subset or their functional state. In addition, miRNAs have been found to be important to regulate innate function of macrophages, dendritic cells and NK cells. The canonical Th1 cytokine, interferon-?(IFN-?), is critical for innate and adaptive immunity against infections, especially for intracellular bacterial infections such as the L. monocytogenes (LM) and M. tuberculosis. A number of complex, interwoven molecular mechanisms have evolved to assure appropriate expression of IFN-?. We found that miR-29a and miR-29b are downregulated in IFN-?-secreting T cells. On the basis of the experimental observations and the predication of IFN-?as potential target of miR-29, we hypothesized that the activation-induced downregulation of miR-29 may in turn facilitate the IFN-? production in these activated cells.Here we report that miR-29 participates in the regulation of NK cell function and Thl response by directly targeting IFN-y mRNA. Knockdown or overexpression of miR-29 facilitated or inhibited the IFN-y production, respectively. The miR-29 sponge transgenic mice, in which the endogenous miR29 was sequestrated in vivo, mounted more potent innate immune response against LM infection, and also stronger Thl response and increased DTH against Bacillus Calmette-Guerin (BCG) infection. Collectively, we demonstrate that miR-29 can suppress both innate and adaptive immune responses against intracellular pathogens by targeting IFN-y, providing a new mechanism for posttranscriptional regulation of IFN-y production and IFN-y-mediated immune responses.