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      MicroRNAs: Biological Regulators in Pathogen–Host Interactions

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          Abstract

          An inflammatory response is essential for combating invading pathogens. Several effector components, as well as immune cell populations, are involved in mounting an immune response, thereby destroying pathogenic organisms such as bacteria, fungi, viruses, and parasites. In the past decade, microRNAs (miRNAs), a group of noncoding small RNAs, have emerged as functionally significant regulatory molecules with the significant capability of fine-tuning biological processes. The important role of miRNAs in inflammation and immune responses is highlighted by studies in which the regulation of miRNAs in the host was shown to be related to infectious diseases and associated with the eradication or susceptibility of the infection. Here, we review the biological aspects of microRNAs, focusing on their roles as regulators of gene expression during pathogen–host interactions and their implications in the immune response against Leishmania, Trypanosoma, Toxoplasma, and Plasmodium infectious diseases.

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          Most cited references124

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          Microarray analysis shows that some microRNAs downregulate large numbers of target mRNAs.

          MicroRNAs (miRNAs) are a class of noncoding RNAs that post-transcriptionally regulate gene expression in plants and animals. To investigate the influence of miRNAs on transcript levels, we transfected miRNAs into human cells and used microarrays to examine changes in the messenger RNA profile. Here we show that delivering miR-124 causes the expression profile to shift towards that of brain, the organ in which miR-124 is preferentially expressed, whereas delivering miR-1 shifts the profile towards that of muscle, where miR-1 is preferentially expressed. In each case, about 100 messages were downregulated after 12 h. The 3' untranslated regions of these messages had a significant propensity to pair to the 5' region of the miRNA, as expected if many of these messages are the direct targets of the miRNAs. Our results suggest that metazoan miRNAs can reduce the levels of many of their target transcripts, not just the amount of protein deriving from these transcripts. Moreover, miR-1 and miR-124, and presumably other tissue-specific miRNAs, seem to downregulate a far greater number of targets than previously appreciated, thereby helping to define tissue-specific gene expression in humans.
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            Regulation by let-7 and lin-4 miRNAs results in target mRNA degradation.

            MicroRNAs (miRNAs) are approximately 22 nucleotide RNAs that negatively regulate the expression of protein-coding genes. In a present model of miRNA function in animals, miRNAs that form imperfect duplexes with their targets inhibit protein expression without affecting mRNA levels. Here, we report that in C. elegans, regulation by the let-7 miRNA results in degradation of its lin-41 target mRNA, despite the fact that its 3'UTR regulatory sequences can only partially base-pair with the miRNA. Furthermore, lin-14 and lin-28 are targets of the lin-4 miRNA, and we show that the mRNA levels for these protein-coding genes significantly decrease in response to lin-4 expression. This study reveals that mRNAs containing partial miRNA complementary sites can be targeted for degradation in vivo, raising the possibility that regulation at the level of mRNA stability may be more common than previously appreciated for the miRNA pathway.
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              Inhibition of translational initiation by Let-7 MicroRNA in human cells.

              MicroRNAs (miRNAs) are approximately 21-nucleotide-long RNA molecules regulating gene expression in multicellular eukaryotes. In metazoa, miRNAs act by imperfectly base-pairing with the 3' untranslated region of target messenger RNAs (mRNAs) and repressing protein accumulation by an unknown mechanism. We demonstrate that endogenous let-7 microribonucleoproteins (miRNPs) or the tethering of Argonaute (Ago) proteins to reporter mRNAs in human cells inhibit translation initiation. M(7)G-cap-independent translation is not subject to repression, suggesting that miRNPs interfere with recognition of the cap. Repressed mRNAs, Ago proteins, and miRNAs were all found to accumulate in processing bodies. We propose that localization of mRNAs to these structures is a consequence of translational repression.
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                Author and article information

                Journal
                Cells
                Cells
                cells
                Cells
                MDPI
                2073-4409
                02 January 2020
                January 2020
                : 9
                : 1
                : 113
                Affiliations
                Department of Physiology, Universidade de São Paulo, 05508-090 São Paulo, Brazil; stephanie.acuna@ 123456usp.br (S.M.A.); lucile@ 123456usp.br (L.M.F.-W.)
                Author notes
                [* ]Correspondence: sandrammuxel@ 123456usp.br ; Tel.: +55-11-3091-7503
                Author information
                https://orcid.org/0000-0001-6074-4077
                https://orcid.org/0000-0003-0118-5361
                Article
                cells-09-00113
                10.3390/cells9010113
                7016591
                31906500
                b2b15ce3-c5f9-40d6-9e71-6b5b95243698
                © 2020 by the authors.

                Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license ( http://creativecommons.org/licenses/by/4.0/).

                History
                : 29 November 2019
                : 19 December 2019
                Categories
                Review

                micrornas,gene expression,post-transcriptional,pathogen,parasite,host,immune response

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