**5. miRNAs and the inhibition of viral replication**

The miRNAs generally induce translational repression by binding to target mRNAs. Thus, it is not surprising that most of the miRNAs identified so far have DENV replication. The evidence points to the fact that miRNAs bind complementarily to the DENV 5'UTR or 3'UTR genome and thus inhibit DENV replication. The miR-548 g-3p represented the first evidence that a miRNA suppresses DENV multiplication by directly linking it to the viral genome. In the study, they showed that miR-548 g-3p was able to bind to the stem-loop A (SLA) promoter at 5'UTR, which is a crucial element for DENV RNA synthesis and replication, and uncontrolled replication of DENV-1. This inhibitory effect was proposed to arise from the binding of miR-548 g-3p to SLA, which could make it physically difficult, and thus attenuated the interaction between the SLA promoter and NS5. This DENV protein contains a C-dependent RNA-terminal RNA polymerase domain [45, 47].

Their hypothesis suggests that a functional miRNA has been preserved among all DENV serotypes and is present in the 3'UTR. The three dengue serotypes, miR-133a, miR-484, and miR-744, are involved in DENV replication, genome circularization, and viral viability. The overexpression of miR-133a, miR-484, and miR-744 in Vero cells had been experimentally validated to show the potencies of these three miRNAs in inhibiting DENV replication [48]. In another study, it found that miR-252 can inhibit DENV-2 replication in cell culture. The identification of protein E as a target for this miRNA is interesting since it has an indispensable role for viral entry [49, 50].

## **6. miRNAs that modulate host factors to inhibit or facilitate DENV replication**

The DENV virus depends on its host's machinery for replication and infection, and it is not surprising that several miRNAs have shown to indirectly regulate DENV replication through modulation of host factors or the immune response. These indirect effects included modulation of the expression of a cell transcript that encodes a host factor necessary for one or a few stages of the viral cycle. The modulation of receptor expression can regulate virus entry, tropism, and essential cofactors for replication or translation that can impair or increase viral replication and the production of viral proteins. Also, miRNAs can increase or restrict cellular responses to viral infection, such as immune response or defense mechanisms [51].

The miRNA let-7c is highly expressed in Huh-7 cells and may be related to the protection of infected cells from oxidative stress and the response to inflammation after DENV infection. Let-7c has shown to bind directly to the basic transcription factor-1 of the leucine zipper (BACH1), a potent repressor of the anti-inflammatory and antioxidant protein heme oxygenase-1 (HO-1), and to dysregulate infection by DENV-2 and DENV-4. In this way, let-7c is probably able to protect the host from virus-induced infection [49].

In addition to modulating the host's immune response, miRNA may have antiviral actions. An example is miR-223, capable of inhibiting DENV-2 replication; its antiviral effect is probably associated with attenuated expression of the microtubule-destabilizing protein, stathmin 1 (STMN1), a key regulator of protein microtubules that controls microtubule dynamics [52]. The exact mechanism of how STMN1 affected DENV-2 replication is not yet known. However, studies have shown that an intact microtubule network involved in STMN1 sequestration was essential for HMCV to establish an infection. As such, it is highly likely that STMN1 is playing a similar role in establishing controlled microtubule dynamics in the context of DENV infection [53].

It is important to emphasize that despite all studies and the discovery of several miRNAs associated with cell regulation positively or negatively, better clarification of the processes involving miRNAs and DENV is still needed.

#### **6.1 Perspective**

#### *6.1.1 Diagnostic using miRNA*

As already reported in this chapter, several human diseases were induced due to differential miRNA expressions. Recently, several studies have confirmed the vibrant role of miRNAs in the successful regulation of various biological processes through the synergistic effects of the multiple miRNA networks, an integrated way to control an individual gene [17].

Also, several physiological functions (such as development, infection, immune response, inflammation, tumor genesis, and regulation of bone mass) have suggested being controlled by miRNAs. The miRNAs can regulate gene expression at the posttranscriptional level of more than 50% of the protein-coding genes in humans.

The miRNAs were found to play roles in helping and defending viruses. Mammalian miRNA genes generally exist in the noncoding region of the genes. However, they also occur both in the exonic regions of the gene encoding protein 16, and in alternative exon splicing, it can also regulate the expression of miRNA interionic genes. Study results show a role for unregulated autophagy in the pathogenesis of some RNA viruses. In this context, the positive regulation of hsa-miR-31 and the negative regulations of hsa-miR-493, hsa-miR-889, hsa-miR-655, hsa-miR-656, hsamiR-26a-1, hsa-miR-154, hsa-miR-335, hsa-miR-1197, and hsa-miR-146a improve innate antiviral responses in cells infected by the virus [26].

Thus, this study aimed at the expression of these miRNAs during dengue infection; in this way, monitoring possible changes can be used as a complementary diagnostic method for faster interventions that can prevent more severe clinical conditions in patients infected with dengue.

#### *6.1.2 Role of RNAi in dengue therapy*

To date, miRNAs are used against some viruses that cause disease in humans, including influenza viruses, hepatitis C viruses, hepatitis B viruses, human immunodeficiency virus type 1, polio, and DENV. These viruses are characterized by the presence of ssRNA genomes, which are potential targets for RNAi in the cytoplasm. This functional interaction occurred during the removal and replication of viral RNA [15, 54].

Any changes in the miRNA pathway may shed light on why some mosquitoes are specific vectors for arthropod-borne virus infections (arboviruses), while others are not. The first evidence is the interference of Sindbis viruses that express the

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*Dengue Virus and the Relationship with MicroRNAs DOI: http://dx.doi.org/10.5772/intechopen.92453*

the silencing mechanism in plants [55].

replication [41, 42].

blocking viral replication.

**Acknowledgements**

**Conflict of interest**

helped in the preparation of this text.

**Notes/thanks/other declarations**

The authors declare no conflict of interest.

**7. Conclusions**

recombinant part of the non-inconsequential unrelated RNA (DENV-2), with the replication of DENV-2 in mosquitoes (Egyptian Aedes) through a system such as

Potential evidence may be involved with the interaction of dsRNA or siRNA derived from the arbovirus genome. Mammals have thousands of Piwi-interacting RNA genes from producer types of microRNA regulation expression to control the various stages of cell development and physiology. The critical role of RNAi is a defense against viruses in primary organisms, but in mammals, it is the antiviral defense mechanism hitherto controversial. Currently, it is a conserved mechanism of RNAi in mammals, where its introduction to siRNA affects the silent replication of viruses. Currently, the most significant therapeutic attempt using miRNA is to block the "shutdown" actions of genes that end up facilitating viral

It is possible to conclude that miRNA has an important relationship during DENV infection, and this regulation can be positive for the virus, that is, facilitating the entry of the virus and helping in the replication process, but it is important to emphasize that there are miRNAs that can also have antiviral action, thereby

The miRNA studies demonstrate how important this small RNAi is for viral infections, whether in arthropod vectors like mosquitoes or mammals like humans. One of the significant difficulties in the study of miRNA is the difficulty of understanding all of its relationships within the cell. Thus, further studies are needed to elucidate more forcefully what the functions of each miRNA are with the cell cycle and the viral replication cycle. Nevertheless, these RNAs have been bring-

I thank the colleagues who contributed to this work and the institutions that

The authors thank everyone who contributed to the elaboration of this text.

ing great perspectives both in treatment and as markers for DENV.

recombinant part of the non-inconsequential unrelated RNA (DENV-2), with the replication of DENV-2 in mosquitoes (Egyptian Aedes) through a system such as the silencing mechanism in plants [55].

Potential evidence may be involved with the interaction of dsRNA or siRNA derived from the arbovirus genome. Mammals have thousands of Piwi-interacting RNA genes from producer types of microRNA regulation expression to control the various stages of cell development and physiology. The critical role of RNAi is a defense against viruses in primary organisms, but in mammals, it is the antiviral defense mechanism hitherto controversial. Currently, it is a conserved mechanism of RNAi in mammals, where its introduction to siRNA affects the silent replication of viruses. Currently, the most significant therapeutic attempt using miRNA is to block the "shutdown" actions of genes that end up facilitating viral replication [41, 42].
