MicroRNA-155 Modulates the Pathogen Binding Ability of Dendritic Cells (DCs) by Down-regulation of DC-specific Intercellular Adhesion Molecule-3 Grabbing Non-integrin (DC-SIGN)

Abstract

MicroRNA-155 (miR-155) has been involved in the response to inflammation in macrophages and lymphocytes. Here we show how miR-155 participates in the maturation of human dendritic cells (DC) and modulates pathogen binding by downregulating DC-specific intercellular adhesion molecule-3 grabbing non-integrin (DC-SIGN), after directly targeting the transcription factor PU.1. During the maturation of DCs, miR-155 increases up to 130-fold, whereas PU.1 protein levels decrease accordingly. We establish that human PU.1 is a direct target for miR-155 and localize the target sequence for miR-155 in the 3-untranslated region of PU.1. Also, overexpression of miR-155 in the THP1 monocytic cell line decreases PU.1 protein levels and DC-SIGN at both the mRNA and protein levels. We prove a link between the down-regulation of PU.1 and reduced transcriptional activity of the DC-SIGN promoter, which is likely to be the basis for its reduced mRNA expression, after miR-155 overexpression. Finally, we show that, by reducing DC-SIGN in the cellular membrane, miR-155 is involved in regulating pathogen binding as dendritic cells exhibited the lower binding capacity for fungi and HIV protein gp-120 when the levels of miR-155 were higher. Thus, our results suggest a mechanism by which miR-155 regulates proteins involved in the cellular immune response against pathogens that could have clinical implications in the way pathogens enter the human organism.MicroRNAs have emerged as important regulators of key cellular processes. They consist of endogenous small, non-coding RNA molecules of about 19 -22 nucleotides in length (1), which regulate mRNAs in a post-transcriptional manner. They bind to the 3Ј-untranslated regions of their target mRNAs and exert their function in two ways: mainly blocking the translation and also inducing their cleavage in a similar fashion to small interfering RNAs (2). MicroRNAs are initially expressed as long immature pri-microRNAs, which are processed in the nucleus into the precursor pre-microRNAs and finally matured by Dicer in the cytoplasm into the functional 19 -22-nucleotide long microRNAs, which are then incorporated into the RNAinduced silencing complex (1).The role of microRNAs is being intensively studied in many different fields such as fetal development and the immune system. One of the miRNAs that appears to play a particularly important role in the immune system is microRNA-155 (miR-155), 3 the expression of which is induced by inflammatory signals such as exposure to antigen, Toll-like receptor ligands, or interferon ␥ stimulation in T-cells, B-cells, and macrophages, respectively (3, 4). miR-155 knock-out mice show aberrant immune functions including defective B and T cell immunity and abnormal function of antigen-presenting cells (4, 5). These mutant mice exhibit an imbalance in the immune Th1/Th2 response, with the CD4ϩ T cells biased toward Th2 differentiation (4). A lack of miR-155 also leads to a failure in production of high-affinity IgG 1 antibodies by murine B-cells (28). This effect has b...

Functional regulation of monocyte-derived dendritic cells by microRNAs

“…Transcription factor c-Fos as a target of miR-155 was negatively for moDC maturation (Dunand-Sauthier et al, 2011). Similarly for what was described for regulation of IL-6 by miR-155 (Ceppi et al, 2009;O'Connell et al, 2010;Dunand-Sauthier et al, 2011), a positive role for miR-155 in mouse moDC maturation is contrasted by a reported negative role of miR-155 for maturation of human moDC, at least based on DC-Sign expression (Martinez-Nunez et al, 2009). Maturation from monocytes into moDCs was also found to be correlated with decreased miR-211 (Lu et al, 2011a).…”

“…During LPS-mediated moDC maturation, miR-155 is up-regulated. In cell line with over-expressed miR-155, expression levels of transcription factor PU.1 and DC-SIGN was reduced (Martinez-Nunez et al, 2009). Suppression of miR-155 in moDCs increased DC-SIGN expression and improved the binding of HIV protein gp-120 and Candida albicans (Martinez-Nunez et al, 2009).…”

RNA Profiling in Human and Murine Transplanted Hearts: Identification and Validation of Therapeutic Targets for Acute Cardiac and Renal Allograft Rejection

“…Importantly, the pro‐inflammatory effects of miR‐155 during ACR implicate that it targets mRNAs coding for anti‐inflammatory proteins. Intriguingly, our mRNA arrays showed that the 33 dysregulated transcripts involved in the IL‐6 pathway also function downstream of SPI1 18, 25 an established target of miR‐155. Whereas the anti‐inflammatory transcription factor SPI1 decreased during ACR, miR‐155 inhibition de‐repressed SPI1.…”

“…SPI 1 is a distinct leukocytic miR‐155 target implicated in the repression of IL‐6 signaling 24 and acting as an inhibitor of dendritic cell pathogen binding and antigen presentation of dendritic cells to T cells 25. Splenic expression levels of SPI1 decreased in a time‐dependent way (Figure 2K).…”

“…Macrophage activation and dendritic cell maturation require its upregulation 16, 25, 28. Furthermore, miR‐155 functions at the interface of innate and adaptive immunity as miR‐155 deficient dendritic cells are unable to mount appropriate B and T cell responses 14, 16, 23.…”