Role of microRNA-155 in dendritic cells and macrophages: MiR-155 directly targets PU.1 and IL13Rα1

In search of genes differentially expressed between M1 (pro-Th₁ or pro-inflammatory) and M2 (pro-Th₂ or pro-tolerogenic) macrophages, BIC (microRNA 155 hosting gene) was found up regulated under inflammatory conditions. MicroRNAs are non coding RNAs of ~22nt in length that inhibit gene expression upon pairing to the 3’UTR (UnTranslated Region) of target mRNAs. <i>In silico </i>analysis predicted two pro-Th₂ targets for miR-155: PU.1 and IL13Rα1. PU.1 is a transcription factor essential in myelopoiesis and dendritic cells (DCs) that favours a Th₂ profiling; moreover, PU.1 had been shown to regulate the transcription of DC-SIGN (Dendritic Cell-Specific ICAM-3 Grabbing Non-integrin 1) which is a pathogen receptor expressed in DCs controlled by Th₂ stimuli. IL13Rα1 is the chain receptor for the Th₂ cytokine IL-13, which promotes M2 differentiation. Pro Th₁ stimuli cause maturation of DCs, cells that orchestrate the immune response between Th₁ and Th₂ profiles; moreover, Th₁ stimuli cause classical (M1) macrophages activation versus an alternative (M2) one. My hypothesis was that miR-155 contributes to the pro-Th₁ profile by down regulating pro-Th₂ factors. MiR-155 was found up regulated during DC maturation and both PU.1 and IL13Rα1 were demonstrated as direct targets of miR-155. Employing a developed monocytic cell line which harbors a miR-155 transgene under the control of a Tet-On system (THP1-155 cells), both PU.1 and IL13Rα1 were shown to be down regulated following miR-155 induction in these cells. Moreover, THP1-155 cells showed that DC-SIGN transcription is regulated by miR-155 levels through PU.1 targeting, and that IL-13 signalling cascade through STAT6 transcription factor was down regulated when miR-155 was over expressed. Using Anti miR-155 transfections in DCs, miR-155 was shown to modulate not only DC-SIGN expression, but also DC pathogen binding ability. Using the same technique in macrophages, miR-155 was shown to modulate IL13Rα1 and STAT6 activation, and to regulate the expression of IL-13/STAT6 dependent genes. Therefore, miR-155 contributes to the pro-Th₁ profile by down regulating pro-Th₂ factors, acting as a pro-Th₁/anti-Th₂ modulator in myeloid cells under inflammatory conditions.

Name dc:type.qualificationname

Ph.D.

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

University of Southampton

Year dc:date.issued

2010

Author dc:creator

• Martinez‐Nunez, Rocio Teresa

Advisor dc:contributor.advisor

• Sanchez-Elsner, Tilman