Down regulated lncRNA MEG3 eliminates mycobacteria in macrophages via autophagy.

Kamlesh Pawar,Ralf Einspanier,Sergio Eliseo Palma Vera,Carlos Hanisch,Soroush Sharbati

doi:10.1038/srep19416

Abstract

Small non-coding RNA play a major part in host response to bacterial agents. However, the role of long non-coding RNA (lncRNA) in this context remains unknown. LncRNA regulate gene expression by acting e.g. as transcriptional coactivators, RNA decoys or microRNA sponges. They control development, differentiation and cellular processes such as autophagy in disease conditions. Here, we provide an insight into the role of lncRNA in mycobacterial infections. Human macrophages were infected with Mycobacterium bovis BCG and lncRNA expression was studied early post infection. For this purpose, lncRNA with known immune related functions were preselected and a lncRNA specific RT-qPCR protocol was established. In addition to expression-based prediction of lncRNA function, we assessed strategies for thorough normalisation of lncRNA. Arrayed quantification showed infection-dependent repression of several lncRNA including MEG3. Pathway analysis linked MEG3 to mTOR and PI3K-AKT signalling pointing to regulation of autophagy. Accordingly, IFN-γ induced autophagy in infected macrophages resulted in sustained MEG3 down regulation and lack of IFN-γ allowed for counter regulation of MEG3 by viable M. bovis BCG. Knockdown of MEG3 in macrophages resulted in induction of autophagy and enhanced eradication of intracellular M. bovis BCG.

Highlights

LncRNA frequently localise in the nucleus functioning both in cis as well as in trans, which points to potential functions as interfaces with the epigenetic machinery, chromatin organisation and regulation of gene expression
They function e.g. as protein scaffolds, activators or inhibitors of transcription, antisense RNA or miRNA sponges, respectively[13,14]. The latter has been reported recently as a novel mode of action of lncRNA, where they act as a competing endogenous RNA. This suggests the existence of a network of lncRNA and mRNA, which crosstalk based on mutual miRNA response elements (MRE)[15]
We have reported earlier that in M. avium infection of human macrophages inhibition of apoptosis is grounded in let-7e and miR-29a mediated regulation of CASP3 and 75

Summary

Introduction

LncRNA frequently localise in the nucleus functioning both in cis (at the site of their transcription) as well as in trans (at the sites on other chromosomes), which points to potential functions as interfaces with the epigenetic machinery, chromatin organisation and regulation of gene expression. It has been shown that decreased expression of the lncRNA MEG3 results in activation of autophagy in bladder cancer cells[17]. Among all down regulated lncRNA at 30 min, MEG3 showed most pronounced and significantly decreased expression having more than 10-fold lower values compared with BCG hk (Fig. 2b, unpaired t test, P < 0.01).

Results

Conclusion