MicroRNAs are a class of small noncoding RNAs that act as major post-transcriptional regulators of gene expression. They are currently recognized for their important role in the intricate interaction ...between host and bacterial pathogens, either as part of the host immune response to neutralize infection, or as a molecular strategy employed by bacteria to hijack host pathways for their own benefit. Here, we summarize recent advances on the function of miRNAs during infection of mammalian hosts by bacterial pathogens, highlighting key cellular pathways. In addition, we discuss emerging themes in this field, including the participation of miRNAs in host–microbiota crosstalk and cell-to-cell communication.
MiRNAs have recently emerged as major players in the interactions between host and bacterial pathogens.
Several host functions have been shown to be regulated by miRNAs during infection, including cell cycle, cytoskeleton organization, autophagy, cell death, and survival.
MiRNAs are an integral part of the host immune response to bacterial infection.
Bacterial pathogens subvert host miRNA expression for their own benefit, promoting survival, replication, and persistence.
A growing number of studies indicate that gut microbiota can influence the miRNome, and vice-versa.
MicroRNAs (miRNAs) are small non-coding RNAs with a central role in the post-transcriptional control of gene expression, that have been implicated in a wide-range of biological processes. Regulation ...of miRNA expression is increasingly recognized as a crucial part of the host response to infection by bacterial pathogens, as well as a novel molecular strategy exploited by bacteria to manipulate host cell pathways. Here, we review the current knowledge of bacterial pathogens that modulate host miRNA expression, focusing on mammalian host cells, and the implications of miRNA regulation on the outcome of infection. The emerging role of commensal bacteria, as part of the gut microbiota, on host miRNA expression in the presence or absence of bacterial pathogens is also discussed.
In mammals, enlargement of the heart during embryonic development is primarily dependent on the increase in cardiomyocyte numbers. Shortly after birth, however, cardiomyocytes stop proliferating and ...further growth of the myocardium occurs through hypertrophic enlargement of the existing myocytes. As a consequence of the minimal renewal of cardiomyocytes during adult life, repair of cardiac damage through myocardial regeneration is very limited. Here we show that the exogenous administration of selected microRNAs (miRNAs) markedly stimulates cardiomyocyte proliferation and promotes cardiac repair. We performed a high-content microscopy, high-throughput functional screening for human miRNAs that promoted neonatal cardiomyocyte proliferation using a whole-genome miRNA library. Forty miRNAs strongly increased both DNA synthesis and cytokinesis in neonatal mouse and rat cardiomyocytes. Two of these miRNAs (hsa-miR-590 and hsa-miR-199a) were further selected for testing and were shown to promote cell cycle re-entry of adult cardiomyocytes ex vivo and to promote cardiomyocyte proliferation in both neonatal and adult animals. After myocardial infarction in mice, these miRNAs stimulated marked cardiac regeneration and almost complete recovery of cardiac functional parameters. The miRNAs identified hold great promise for the treatment of cardiac pathologies consequent to cardiomyocyte loss.
The YAP and TAZ mediators of the Hippo pathway (hereafter called YAP/TAZ) promote tissue proliferation and organ growth. However, how their biological properties intersect with cellular metabolism ...remains unexplained. Here, we show that YAP/TAZ activity is controlled by the SREBP/mevalonate pathway. Inhibition of the rate-limiting enzyme of this pathway (HMG-CoA reductase) by statins opposes YAP/TAZ nuclear localization and transcriptional responses. Mechanistically, the geranylgeranyl pyrophosphate produced by the mevalonate cascade is required for activation of Rho GTPases that, in turn, activate YAP/TAZ by inhibiting their phosphorylation and promoting their nuclear accumulation. The mevalonate-YAP/TAZ axis is required for proliferation and self-renewal of breast cancer cells. In Drosophila melanogaster, inhibition of mevalonate biosynthesis and geranylgeranylation blunts the eye overgrowth induced by Yorkie, the YAP/TAZ orthologue. In tumour cells, YAP/TAZ activation is promoted by increased levels of mevalonic acid produced by SREBP transcriptional activity, which is induced by its oncogenic cofactor mutant p53. These findings reveal an additional layer of YAP/TAZ regulation by metabolic cues.
Sterol regulatory element binding proteins (SREBPs) are a family of transcription factors that regulate lipid biosynthesis and adipogenesis by controlling the expression of several enzymes required ...for cholesterol, fatty acid, triacylglycerol and phospholipid synthesis. In vertebrates, SREBP activation is mainly controlled by a complex and well-characterized feedback mechanism mediated by cholesterol, a crucial bio-product of the SREBP-activated mevalonate pathway. In this work, we identified acto-myosin contractility and mechanical forces imposed by the extracellular matrix (ECM) as SREBP1 regulators. SREBP1 control by mechanical cues depends on geranylgeranyl pyrophosphate, another key bio-product of the mevalonate pathway, and impacts on stem cell fate in mouse and on fat storage in Drosophila. Mechanistically, we show that activation of AMP-activated protein kinase (AMPK) by ECM stiffening and geranylgeranylated RhoA-dependent acto-myosin contraction inhibits SREBP1 activation. Our results unveil an unpredicted and evolutionary conserved role of SREBP1 in rewiring cell metabolism in response to mechanical cues.
The Hippo pathway is an oncosuppressor signalling cascade that plays a major role in the control of cell growth, tissue homoeostasis and organ size. Dysregulation of the Hippo pathway leads to ...aberrant activation of the transcription co-activator YAP (Yes-associated protein) that contributes to tumorigenesis in several tissues. Here we identify glucocorticoids (GCs) as hormonal activators of YAP. Stimulation of glucocorticoid receptor (GR) leads to increase of YAP protein levels, nuclear accumulation and transcriptional activity in vitro and in vivo. Mechanistically, we find that GCs increase expression and deposition of fibronectin leading to the focal adhesion-Src pathway stimulation, cytoskeleton-dependent YAP activation and expansion of chemoresistant cancer stem cells. GR activation correlates with YAP activity in human breast cancer and predicts bad prognosis in the basal-like subtype. Our results unveil a novel mechanism of YAP activation in cancer and open the possibility to target GR to prevent cancer stem cells self-renewal and chemoresistance.
Loss of functional cardiomyocytes is a major determinant of heart failure after myocardial infarction. Previous high throughput screening studies have identified a few microRNAs (miRNAs) that can ...induce cardiomyocyte proliferation and stimulate cardiac regeneration in mice. Here, we show that all of the most effective of these miRNAs activate nuclear localization of the master transcriptional cofactor Yes-associated protein (YAP) and induce expression of YAP-responsive genes. In particular, miR-199a-3p directly targets two mRNAs coding for proteins impinging on the Hippo pathway, the upstream YAP inhibitory kinase TAOK1, and the E3 ubiquitin ligase β-TrCP, which leads to YAP degradation. Several of the pro-proliferative miRNAs (including miR-199a-3p) also inhibit filamentous actin depolymerization by targeting Cofilin2, a process that by itself activates YAP nuclear translocation. Thus, activation of YAP and modulation of the actin cytoskeleton are major components of the pro-proliferative action of miR-199a-3p and other miRNAs that induce cardiomyocyte proliferation.
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•A few microRNAs can stimulate cardiac myocyte proliferation•The most effective of these microRNAs activate YAP•Several pro-proliferative microRNAs also inhibit actin depolymerization•miR-199a-3p directly targets TAOK1, b-TrCP, and Cofilin2 to achieve its effects
Torrini et al. report that several microRNAs that induce cardiomyocyte proliferation act by stimulating activation of the transcriptional cofactor YAP, a master regulator of cell proliferation. Several microRNAs also act on the cardiomyocyte cytoskeleton by promoting actin polymerization. These microRNAs can be considered as potential treatments for cardiac regeneration.
Increasing evidence suggests an important role for miRNAs in the molecular interplay between bacterial pathogens and host cells. Here we perform a fluorescence microscopy-based screen using a library ...of miRNA mimics and demonstrate that miRNAs modulate Salmonella infection. Several members of the miR-15 miRNA family were among the 17 miRNAs that more efficiently inhibit Salmonella infection. We discovered that these miRNAs are downregulated during Salmonella infection, through the inhibition of the transcription factor E2F1. Analysis of miR-15 family targets revealed that derepression of cyclin D1 and the consequent promotion of G1/S transition are crucial for Salmonella intracellular proliferation. In addition, Salmonella induces G2/M cell cycle arrest in infected cells, further promoting its replication. Overall, these findings uncover a mechanism whereby Salmonella renders host cells more susceptible to infection by controlling cell cycle progression through the active modulation of host cell miRNAs.
Viral vectors based on the adeno-associated virus (AAV) hold great promise for in vivo gene transfer; several unknowns, however, still limit the vectors’ broader and more efficient application. Here, ...we report the results of a high-throughput, whole-genome siRNA screening aimed at identifying cellular factors regulating AAV transduction. We identified 1,483 genes affecting vector efficiency more than 4-fold and up to 50-fold, either negatively or positively. Most of these factors have not previously been associated to AAV infection. The most effective siRNAs were independent from the virus serotype or analyzed cell type and were equally evident for single-stranded and self-complementary AAV vectors. A common characteristic of the most effective siRNAs was the induction of cellular DNA damage and activation of a cell cycle checkpoint. This information can be exploited for the development of more efficient AAV-based gene delivery procedures. Administration of the most effective siRNAs identified by the screening to the liver significantly improved in vivo AAV transduction efficiency.
Productive HIV-1 replication requires viral integrase (IN), which catalyzes integration of the viral genome into the host cell DNA. IN, however, is short lived and is rapidly degraded by the host ...ubiquitin-proteasome system. To identify the cellular factors responsible for HIV-1 IN degradation, we performed a targeted RNAi screen using a library of siRNAs against all components of the ubiquitin-conjugation machinery using high-content microscopy. Here we report that the E3 RING ligase TRIM33 is a major determinant of HIV-1 IN stability. CD4-positive cells with TRIM33 knock down show increased HIV-1 replication and proviral DNA formation, while those overexpressing the factor display opposite effects. Knock down of TRIM33 reverts the phenotype of an HIV-1 molecular clone carrying substitution of IN serine 57 to alanine, a mutation known to impair viral DNA integration. Thus, TRIM33 acts as a cellular factor restricting HIV-1 infection by preventing provirus formation.
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