Cellular MicroRNA Let-7a Suppresses KSHV Replication through Targeting MAP4K4 Signaling Pathways

MicroRNA let-7a regulation of Hantaan virus replication by Targeting FAS Signaling Pathways

Hantaan virus (HTNV) infection in humans can cause hemorrhagic fever and renal syndrome (HFRS). Understanding host responses to HTNV infection is crucial for developing effective disease intervention strategies. Previous RNA-sequencing studies have investigated the role of microRNAs (miRNAs) in the post-transcriptional regulation of host genes in response to HTNV infection. In this study, we demonstrated that HTNV infection induces let-7a expression in human umbilical vein endothelial cells (HUVEC) and that HTNV G protein upregulates the expression of let-7a. miRNA let-7a mimics and inhibitors validated the predicted targets, including cell apoptosis genes (FAS, caspase-8, and caspase-3) and inflammatory factors (IL-6 and its related factors). Modulation of miRNA let-7a levels by miRNA mimics and inhibitors affected HTNV replication, indicating that HTNV modulates host miRNA expression to affect the outcome of the antiviral host response.

Dichotomous role of the serine/threonine kinase MAP4K4 in pancreatic ductal adenocarcinoma onset and metastasis through control of AKT and ERK pathways

MAP4K4 is a serine/threonine kinase of the STE20 family involved in the regulation of actin cytoskeleton dynamics and cell motility. It has been proposed as a target of angiogenesis and inhibitors show potential in cardioprotection. MAP4K4 also mediates cell invasion in vitro, is overexpressed in various types of cancer, and is associated with poor patient prognosis. Recently, MAP4K4 has been shown to be overexpressed in pancreatic cancer, but its role in tumour initiation, progression, and metastasis is unknown. Here, using the KrasG12D Trp53R172H Pdx1-Cre (KPC) mouse model of pancreatic ductal adenocarcinoma (PDAC), we show that deletion of Map4k4 drives tumour initiation and progression. Moreover, we report that the acceleration of tumour onset is also associated with an overactivation of ERK and AKT, two major downstream effectors of KRAS, in vitro and in vivo. In contrast to the accelerated tumour onset caused by loss of MAP4K4, we observed a reduction in metastatic burden with both the KPC model and in an intraperitoneal transplant assay indicating a major role of MAP4K4 in metastatic seeding. In summary, our study sheds light on the dichotomous role of MAP4K4 in the initiation of PDAC onset, progression, and metastatic dissemination. It also identifies MAP4K4 as a possible druggable target against pancreatic cancer spread, but with the caveat that targeting MAP4K4 might accelerate early tumorigenesis. © 2024 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Map4k4 is up-regulated and modulates granulosa cell injury and oxidative stress in polycystic ovary syndrome via activating JNK/c-JUN pathway: An experimental study

The regulatory mechanism on granulosa cells (GCs) oxidative injury is becoming increasingly important in polycystic ovary syndrome (PCOS) studies. Serine/threonine kinase mitogen-activated protein 4 kinase 4 (Map4k4) is linked with oxidative injury and possibly associated with premature ovarian failure and ovarian dysgenesis. Herein, we investigated the function and mechanism of Map4k4 in a PCOS rat model. A microarray from GEO database identified Map4k4 was up-regulated in the ovarian of PCOS rats, and functional enrichments suggested that oxidative stress-associated changes are involved. We verified the raised Map4k4 expression in an established PCOS rat model and also in the isolated PCOS-GCs, which were consistent with the microarray data. Map4k4 knockdown in vivo contributed to regular estrous cycle, restrained steroid concentrations and ovarian injury in PCOS rats. Both Map4k4 silencing in vivo and in vitro attenuated the PCOS-related GC oxidative stress and apoptosis. Mechanically, Map4k4 activated the JNK/c-JUN signaling pathway. Importantly, a JNK agonist restored the suppressive effects of Map4k4 silencing on PCOS-induced granulosa cell injury and oxidative stress. Besides, Map4k4 may be a target gene of miR-185-5p. In conclusion, Map4k4, a potential target of miR-185-5p, is up-regulated and induces ovarian GC oxidative injury by activating JNK/c-JUN pathway in PCOS. The Map4k4/JNK/c-JUN mechanism may provide a new idea on the treatment of PCOS.

Loss of SETD2-mediated downregulation of intracellular and exosomal miRNA-10b determines MAPK pathway activation and multidrug resistance in renal cancer

SET domain-containing 2 (SETD2) is the most frequently mutated gene among all the histone methyltransferases in clear cell renal cell carcinoma (ccRCC). Microarrays, RNA sequencing analysis and exosomes analysis of cellular supernatant were performed after transfection A498 cells with si-SETD2 or siRNA of negative control. Chromatin immunoprecipitation and Luciferase reporter assay were conducted to evaluate the interaction between SETD2 and miR-10b. Functional and drug experiments in vitro and in vivo were performed to verify the role of SETD2, miR-10b and MAP4K4. The results showed that loss of SETD2 mediated downregulation of intracellular and exosomal microRNA-10b. MAP4K4 were relevant to oncogenesis of ccRCC caused by loss of SETD2 and miR-10b. SETD2 could directly target miR-10b and regulate the expression of multidrug resistance (MDR)-1 (P-gp170) through JNK pathway, which was one of the downstream pathways of MAP4K4. The coordinated expression of SETD2/H3K36me3/miR-10b/MAPKs/JNK/MDR pathway was revealed to the progression of ccRCC.

Inhibition of MAP4K4 Signaling Initiaties Metabolic Reprogramming to Protect Hepatocytes from Lipotoxic Damage

The primary hepatic consequence of obesity is non-alcoholic fatty liver disease (NAFLD), affecting about 25% of the global adult population. Non-alcoholic steatohepatitis (NASH) is a severe form of NAFLD characterized by liver lipid accumulation, inflammation, and hepatocyte ballooning, with a different degree of hepatic fibrosis. In the light of rapidly increasing prevalence of NAFLD and NASH, there is an urgent need for improved understanding of the molecular pathogenesis of these diseases. The aim of this study was to decipher the possible role of STE20-type kinase MAP4K4 in the regulation of hepatocellular lipotoxicity and susceptibility to NAFLD. We found that MAP4K4 mRNA expression in human liver biopsies was positively correlated with key hallmarks of NAFLD (i.e., liver steatosis, lobular inflammation, hepatocellular ballooning, and fibrosis). We also found that the silencing of MAP4K4 suppressed lipid deposition in human hepatocytes by stimulating β-oxidation and triacylglycerol secretion, while attenuating fatty acid influx and lipid synthesis. Furthermore, downregulation of MAP4K4 markedly reduced the glycolysis rate and lowered incidences of oxidative/endoplasmic reticulum stress. In parallel, we observed suppressed JNK and ERK and increased AKT phosphorylation in MAP4K4-deficient hepatocytes. Together, these results provide the first experimental evidence supporting the potential involvement of STE20-type kinase MAP4K4 as a component of the hepatocellular lipotoxic milieu promoting NAFLD susceptibility.

Kaposi's sarcoma-associated herpes virus-derived microRNA K12-1 over-activates the PI3K/Akt pathway to facilitate cancer progression in HIV-related gastrointestinal Kaposi's sarcoma

BACKGROUND

Kaposi's sarcoma-associated herpes virus (KSHV) initiate and accelerate the development of Kaposi's sarcoma (KS), and KSHV possesses many cancer-associated genes, including KSHV-derived microRNA miR-K12-1, which has been identified to be closely associated with KS progression. However, the detailed mechanisms by which miR-K12-1 facilitates HIV-related gastrointestinal KS development are still not fully delineated.

OBJECTIVES

This study strived to evaluate the effect of miR-K12-1 on the progression of HIV-related gastrointestinal KS.

MATERIALS AND METHODS

The expression levels of miR-K12-1 in HIV-related gastrointestinal KS tissues were determined by RT-qPCR. Proliferation and apoptosis were assessed by colony formation, CCK-8 and flow cytometry, respectively. The expression of all proteins was detected by Western blot. The in vivo effect of miR-K12-1 on the formation of a tumor was explored by using the mouse xenograft model.

RESULTS

In this study, we uncovered that KSHV-miR-K12-1 was upregulated in HIV-related gastrointestinal KS tissues and associated with poor outcome in HIV-related gastrointestinal KS patients. Compared with the control group, after miR-K12-1 inhibitor transfection, BCBL-1 cell viability was decreased, and the cell apoptosis was significantly increased, whereas transfection of miR-K12-1 mimics promoted cell proliferation and mitosis. In addition, our rescuing experiments verified that miR-K12-1 promoted cell proliferation via activating the PI3K/Akt pathway, and inhibition of the PI3K/Akt pathway by LY294002 abrogated the tumor-promoting effects of miR-K12-1 in HIV-related gastrointestinal KS.

CONCLUSIONS

In summary, we concluded that KSHV-derived miR-K12-1 activate the PI3K/Akt pathway to initiate and accelerate the development of KS, which convinces us that miR-K12-1 can be used as potential biomarkers for KS diagnosis, treatment and prognosis.

MircroRNA Let-7a-5p in Airway Smooth Muscle Cells is Most Responsive to High Stretch in Association With Cell Mechanics Modulation

Objective: High stretch (strain >10%) can alter the biomechanical behaviors of airway smooth muscle cells which may play important roles in diverse lung diseases such as asthma and ventilator-induced lung injury. However, the underlying modulation mechanisms for high stretch-induced mechanobiological responses in ASMCs are not fully understood. Here, we hypothesize that ASMCs respond to high stretch with increased expression of specific microRNAs (miRNAs) that may in turn modulate the biomechanical behaviors of the cells. Thus, this study aimed to identify the miRNA in cultured ASMCs that is most responsive to high stretch, and subsequently investigate in these cells whether the miRNA expression level is associated with the modulation of cell biomechanics.

Methods: MiRNAs related to inflammatory airway diseases were obtained via bioinformatics data mining, and then tested with cultured ASMCs for their expression variations in response to a cyclic high stretch (13% strain) simulating in vivo ventilator-imposed strain on airways. Subsequently, we transfected cultured ASMCs with mimics and inhibitors of the miRNA that is most responsive to the high stretch, followed by evaluation of the cells in terms of morphology, stiffness, traction force, and mRNA expression of cytoskeleton/focal adhesion-related molecules.

Results: 29 miRNAs were identified to be related to inflammatory airway diseases, among which let-7a-5p was the most responsive to high stretch. Transfection of cultured human ASMCs with let-7a-5p mimics or inhibitors led to an increase or decrease in aspect ratio, stiffness, traction force, migration, stress fiber distribution, mRNA expression of α-smooth muscle actin (SMA), myosin light chain kinase, some subfamily members of integrin and talin. Direct binding between let-7a-5p and ItgαV was also verified in classical model cell line by using dual-luciferase assays.

Conclusion: We demonstrated that high stretch indeed enhanced the expression of let-7a-5p in ASMCs, which in turn led to changes in the cells’ morphology and biomechanical behaviors together with modulation of molecules associated with cytoskeletal structure and focal adhesion. These findings suggest that let-7a-5p regulation is an alternative mechanism for high stretch-induced effect on mechanobiology of ASMCs, which may contribute to understanding the pathogenesis of high stretch-related lung diseases.

MicroRNA let-7 and viral infections: focus on mechanisms of action

MicroRNAs (miRNAs) are fundamental post-transcriptional modulators of several critical cellular processes, a number of which are involved in host defense mechanisms. In particular, miRNA let-7 functions as an essential regulator of the function and differentiation of both innate and adaptive immune cells. Let-7 is involved in several human diseases, including cancer and viral infections. Several viral infections have found ways to dysregulate the expression of miRNAs. Extracellular vesicles (EV) are membrane-bound lipid structures released from many types of human cells that can transport proteins, lipids, mRNAs, and miRNAs, including let-7. After their release, EVs are taken up by the recipient cells and their contents released into the cytoplasm. Let-7-loaded EVs have been suggested to affect cellular pathways and biological targets in the recipient cells, and can modulate viral replication, the host antiviral response, and the action of cancer-related viruses. In the present review, we summarize the available knowledge concerning the expression of let-7 family members, functions, target genes, and mechanistic involvement in viral pathogenesis and host defense. This may provide insight into the development of new therapeutic strategies to manage viral infections.

RTA and LANA Competitively Regulate let-7a/RBPJ Signal to Control KSHV Replication

The recombination signal binding protein for immunoglobulin kappa J region (RBPJ) has a dual effect on Kaposi's sarcoma-associated herpesvirus (KSHV) replication. RBPJ interaction with replication and transcription activator (RTA) is essential for lytic replication, while the interaction with latency-associated nuclear antigen (LANA) facilitates latent infection. Furthermore, our previous study found that LANA decreased RBPJ through upregulating miRNA let-7a. However, it is unclear whether RTA regulates the expression of RBPJ. Here, we show RTA increases RBPJ by decreasing let-7a. During KSHV replication, the RBPJ expression level was positively correlated with the RTA expression level and negatively correlated with the LANA expression level. The let-7a expression level was inverse to RBPJ. Knockdown of RBPJ inhibited the self-activation of RTA promoter and LANA promoter and weakened LANA's inhibition of RTA promoter. Collectively, these findings indicate that RTA and LANA compete for let-7a/RBPJ signal to control the KSHV replication. Regulating the RBPJ expression level by RTA and LANA plays an important role during KSHV replication.

RETRACTED: Mouse bone marrow derived mesenchymal stem cells-secreted exosomal microRNA-125b-5p suppresses atherosclerotic plaque formation via inhibiting Map4k4

This article has been retracted: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). This article has been retracted at the request of the Editor-in-Chief. Concern was raised about the reliability of the Western blot results in Figs. 2D and 4E, which appear to have the same eyebrow shaped phenotype as many other publications tabulated here (https://docs.google.com/spreadsheets/d/149EjFXVxpwkBXYJOnOHb6RhAqT4a2llhj9LM60MBffM/edit#gid=0). The journal requested the corresponding author comment on these concerns and provide the raw data. However the authors were not able to satisfactorily fulfil this request and therefore the Editor-in-Chief decided to retract the article.

miRNAs and Leukotrienes in Respiratory Syncytial Virus Infection

MicroRNAs (miRNAs) are small, non-coding RNAs that regulate posttranscription by binding to 3'-untranslated regions of target mRNAs. Recent functional studies have elucidated mechanisms that miRNAs regulate leukotriene synthesis by perturbing arachidonic acid metabolism. Both microarrays and high-throughput sequencing revealed distinct differential expression of miRNAs in children with respiratory syncytial virus (RSV) infection compared with healthy controls. Abnormal miRNA expression may contribute to higher leukotriene levels, which is associated with airway hyperreactivity. Targeting miRNAs may benefit to restore the homeostasis of inflammatory reaction and provide new strategies to alleviate airway hyperreactivity induced by RSV. In this article, we provide an overview of the current knowledge about miRNAs modulating leukotrienes through regulation of arachidonic acid metabolism with a special focus on miRNAs aberrantly expressed in children with RSV infection.

Interactions of Monocytes, HIV, and ART Identified by an Innovative scRNAseq Pipeline: Pathways to Reservoirs and HIV-Associated Comorbidities

HIV reservoirs persist despite successful antiretroviral therapy (ART) and are a major obstacle to the eradication and cure of HIV. The mature monocyte subset, CD14+CD16+, contributes to viral reservoirs and HIV-associated comorbidities. Only a subset of monocytes harbors HIV (HIV+), while the rest remain uninfected, exposed cells (HIVexp). We developed an innovative single cell RNA sequencing (scRNAseq) pipeline that detects HIV and host transcripts simultaneously, enabling us to examine differences between HIV+ and HIVexp mature monocytes. Using this, we characterized uninfected, HIV+, and HIVexp primary human mature monocytes with and without ART. We showed that HIV+ mature monocytes do not form their own cluster separately from HIVexp but can be distinguished by significant differential gene expression. We found that ART decreased levels of unspliced HIV transcripts potentially by modulating host transcriptional regulators shown to decrease viral infection and replication. We also identified and characterized mature monocyte subpopulations differentially impacted by HIV and ART. We identified genes dysregulated by ART in HIVexp monocytes compared to their uninfected counterpart and, of interest, the junctional protein ALCAM, suggesting that ART impacts monocyte functions. Our data provide a novel method for simultaneous detection of HIV and host transcripts. We identify potential targets, such as those genes whose expression is increased in HIV+ mature monocytes compared to HIVexp, to block their entry into tissues, preventing establishment/replenishment of HIV reservoirs even with ART, thereby reducing and/or eliminating viral burden and HIV-associated comorbidities. Our data also highlight the heterogeneity of mature monocyte subsets and their potential contributions to HIV pathogenesis in the ART era.IMPORTANCE HIV enters tissues early after infection, leading to establishment and persistence of HIV reservoirs despite antiretroviral therapy (ART). Viral reservoirs are a major obstacle to the eradication and cure of HIV. CD14+CD16+ (mature) monocytes may contribute to establishment and reseeding of reservoirs. A subset of monocytes, consisting mainly of CD14+CD16+ cells, harbors HIV (HIV+), while the rest remain uninfected, exposed cells (HIVexp). It is important to identify cells harboring virus to eliminate reservoirs. Using an innovative single-cell RNA sequencing (scRNAseq) pipeline to detect HIV and host transcripts simultaneously, we characterized HIV+ and HIVexp primary human mature monocytes with and without ART. HIV+ mature monocytes are not a unique subpopulation but rather can be distinguished from HIVexp by differential gene expression. We characterized mature monocyte subpopulations differently impacted by HIV and ART, highlighting their potential contributions to HIV-associated comorbidities. Our data propose therapeutic targets to block HIV+ monocyte entry into tissues, preventing establishment and replenishment of reservoirs even with ART.

Latency-associated nuclear antigen inhibits lytic replication of Kaposi's sarcoma-associated herpesvirus by regulating let-7a/RBPJ signaling

Latency-associated nuclear antigen (LANA) is the key factor in the establishment and maintenance of latency of Kaposi's sarcoma-associated herpesvirus (KSHV). A cellular protein, recombination signal binding protein for immunoglobulin kappa J region (RBPJ), is essential for the lytic reactivation of KSHV. However, whether RBPJ expression is regulated by KSHV is not clear. Here, we show that LANA upregulates let-7a and its primary transcripts in parallel with its reduction of RBPJ expression. An increase in notch intracellular domain (NICD) and the downregulation of NF-κB and LIN28B contribute to the upregulation of let-7a by LANA. Let-7a represses RBPJ expression by directly binding the 3' untranslated region of RBPJ. Let-7a overexpression or RBPJ knockdown led to a dose- and time-dependent inhibition of lytic reactivation of KSHV. Collectively, these findings support a model wherein LANA inhibits the lytic replication of KSHV by regulating let-7a/RBPJ signaling.

Identification of lead anti-human cytomegalovirus compounds targeting MAP4K4 via machine learning analysis of kinase inhibitor screening data

Chemogenomic approaches involving highly annotated compound sets and cell based high throughput screening are emerging as a means to identify novel drug targets. We have previously screened a collection of highly characterized kinase inhibitors (Khan et al., Journal of General Virology, 2016) to identify compounds that increase or decrease expression of a human cytomegalovirus (HCMV) protein in infected cells. To identify potential novel anti-HCMV drug targets we used a machine learning approach to relate our phenotypic data from the aforementioned screen to kinase inhibition profiling of compounds used in this screen. Several of the potential targets had no previously reported role in HCMV replication. We focused on one potential anti-HCMV target, MAPK4K, and identified lead compounds inhibiting MAP4K4 that have anti-HCMV activity with little cellular cytotoxicity. We found that treatment of HCMV infected cells with inhibitors of MAP4K4, or an siRNA that inhibited MAP4K4 production, reduced HCMV replication and impaired detection of IE2-60, a viral protein necessary for efficient HCMV replication. Our findings demonstrate the potential of this machine learning approach to identify novel anti-viral drug targets, which can inform the discovery of novel anti-viral lead compounds.

Hsa-let-7c controls the committed differentiation of IGF-1-treated mesenchymal stem cells derived from dental pulps by targeting IGF-1R via the MAPK pathways

The putative tumor suppressor microRNA let-7c is extensively associated with the biological properties of cancer cells. However, the potential involvement of let-7c in the differentiation of mesenchymal stem cells has not been fully explored. In this study, we investigated the influence of hsa-let-7c (let-7c) on the proliferation and differentiation of human dental pulp-derived mesenchymal stem cells (DPMSCs) treated with insulin-like growth factor 1 (IGF-1) via flow cytometry, CCK-8 assays, alizarin red staining, real-time RT-PCR, and western blotting. In general, the proliferative capabilities and cell viability of DPMSCs were not significantly affected by the overexpression or deletion of let-7c. However, overexpression of let-7c significantly inhibited the expression of IGF-1 receptor (IGF-1R) and downregulated the osteo/odontogenic differentiation of DPMSCs, as indicated by decreased levels of several osteo/odontogenic markers (osteocalcin, osterix, runt-related transcription factor 2, dentin sialophosphoprotein, dentin sialoprotein, alkaline phosphatase, type 1 collagen, and dentin matrix protein 1) in IGF-1-treated DPMSCs. Inversely, deletion of let-7c resulted in increased IGF-1R levels and enhanced osteo/odontogenic differentiation. Furthermore, the ERK, JNK, and P38 MAPK pathways were significantly inhibited following the overexpression of let-7c in DPMSCs. Deletion of let-7c promoted the activation of the JNK and P38 MAPK pathways. Our cumulative findings indicate that Let-7c can inhibit the osteo/odontogenic differentiation of IGF-1-treated DPMSCs by targeting IGF-1R via the JNK/P38 MAPK signaling pathways.

miRNA-36 inhibits KSHV, EBV, HSV-2 infection of cells via stifling expression of interferon induced transmembrane protein 1 (IFITM1)

Kaposi's sarcoma-associated herpesvirus (KSHV) is etiologically associated with all forms of Kaposi's sarcoma worldwide. Little is currently known about the role of microRNAs (miRNAs) in KSHV entry. We recently demonstrated that KSHV induces a plethora of host cell miRNAs during the early stages of infection. In this study, we show the ability of host cell novel miR-36 to specifically inhibit KSHV-induced expression of interferon induced transmembrane protein 1 (IFITM1) to limit virus infection of cells. Transfecting cells with miR-36 mimic specifically lowered IFITM1 expression and thereby significantly dampening KSHV infection. In contrast, inhibition of miR-36 using miR-36 inhibitor had the direct opposite effect on KSHV infection of cells, allowing enhanced viral infection of cells. The effect of miR-36 on KSHV infection of cells was at a post-binding stage of virus entry. The highlight of this work was in deciphering a common theme in the ability of miR-36 to regulate infection of closely related DNA viruses: KSHV, Epstein-Barr virus (EBV), and herpes simplexvirus-2 (HSV-2). Taken together, we report for the first time the ability of host cell miRNA to regulate internalization of KSHV, EBV, and HSV-2 in hematopoietic and endothelial cells.

Profiling of cellular microRNA responses during the early stages of KSHV infection

Kaposi's sarcoma-associated herpesvirus (KSHV) causes a variety of cancers, including Kaposi's sarcoma (KS), primary effusion lymphoma (PEL), and multicentric Castleman disease (MCD). Host cellular microRNAs (miRNAs) play important post-transcriptional regulatory roles in gene expression and can greatly influence virus-host cell interactions. This study investigated cellular miRNA expression profiles operating in response to early stages of KSHV infection of human Burkitt lymphoma B cells (BJAB). We employed deep sequencing to analyze miRNA expression in KSHV-infected BJAB cells 15 min post infection (PI) and compared this to uninfected BJAB cells. A total of 32 known miRNAs and 28 novel miRNA candidates were differentially expressed in KSHV-infected compared to uninfected BJAB cells. Interestingly, miRNA expression profiles during the early stages of viral infection yielded comparable results when UV-inactivated KSHV was used. The deep sequencing results were further confirmed by performing real-time reverse transcription PCR. The target genes predicted to be regulated by both the known and novel miRNAs are mainly involved in assisting virus entry, inducing critical cell signaling, initiating transcription of immediate early genes, promoting latent infection, and modulating the host immune response. For the first time, we provide insight into the host cellular miRNA expression profiles in response to early stages of KSHV infection of human B cells. Furthermore, this study offers a valuable basis for further investigation on the roles of cellular miRNAs in the KSHV entry process.

MAP4K4: an emerging therapeutic target in cancer

The serine/threonine kinase MAP4K4 is a member of the Ste20p (sterile 20 protein) family. MAP4K4 was initially discovered in 1995 as a key kinase in the mating pathway in Saccharomyces cerevisiae and was later found to be involved in many aspects of cell functions and many biological and pathological processes. The role of MAP4K4 in immunity, inflammation, metabolic and cardiovascular disease has been recognized. Information regarding MAP4K4 in cancers is extremely limited, but increasing evidence suggests that MAP4K4 also plays an important role in cancer and MAP4K4 may represent a novel actionable cancer therapeutic target. This review summarizes our current understanding of MAP4K4 regulation and MAP4K4 in cancer. MAP4K4-specific inhibitors have been recently developed. We hope that this review article would advocate more basic and preclinical research on MAP4K4 in cancer, which could ultimately provide biological and mechanistic justifications for preclinical and clinical test of MAP4K4 inhibitor in cancer patients.

MicroRNA let-7f-5p Inhibits Porcine Reproductive and Respiratory Syndrome Virus by Targeting MYH9

Porcine reproductive and respiratory syndrome virus (PRRSV) is one of the most important viral pathogens in the swine industry. Current antiviral strategies do not effectively prevent and control PRRSV. Recent reports show that microRNAs (miRNAs) play vital roles in viral infections by post transcriptionally regulating the expression of viral or host genes. Our previous research showed that non-muscle myosin heavy chain 9 (MYH9) is an essential factor for PRRSV infection. Using bioinformatic prediction and experimental verification, we demonstrate that MYH9 expression is regulated by the miRNA let-7f-5p, which binds to the MYH9 mRNA 3'UTR and may play an important role during PRRSV infection. To understand how let-7f-5p regulates PRRSV infection, we analyzed the expression pattern of both let-7f-5p and MYH9 in porcine alveolar macrophages (PAMs) after infection with either highly pathogenic PRRSV (HP-PRRSV) or classical type PRRSV (N-PRRSV) using a deep sequencing approach with quantitative real-time PCR validation. Our results showed that both HP-PRRSV and N-PRRSV infection reduced let-7f-5p expression while also inducing MYH9 expression. Furthermore, let-7f-5p significantly inhibited PRRSV replication through suppression of MYH9 expression. These findings not only provide new insights into the pathogenesis of PRRSV, but also suggest potential new antiviral strategies against PRRSV infection.

Precise let-7 expression levels balance organ regeneration against tumor suppression

The in vivo roles for even the most intensely studied microRNAs remain poorly defined. Here, analysis of mouse models revealed that let-7, a large and ancient microRNA family, performs tumor suppressive roles at the expense of regeneration. Too little or too much let-7 resulted in compromised protection against cancer or tissue damage, respectively. Modest let-7 overexpression abrogated MYC-driven liver cancer by antagonizing multiple let-7 sensitive oncogenes. However, the same level of overexpression blocked liver regeneration, while let-7 deletion enhanced it, demonstrating that distinct let-7 levels can mediate desirable phenotypes. let-7 dependent regeneration phenotypes resulted from influences on the insulin-PI3K-mTOR pathway. We found that chronic high-dose let-7 overexpression caused liver damage and degeneration, paradoxically leading to tumorigenesis. These dose-dependent roles for let-7 in tissue repair and tumorigenesis rationalize the tight regulation of this microRNA in development, and have important implications for let-7 based therapeutics.

DOI:http://dx.doi.org/10.7554/eLife.09431.001

The development of animals is guided by the expression of certain genes at critical moments. Many different mechanisms control development; in one of them, the expression of genes can be decreased by molecules called microRNAs. In particular, the group of microRNAs called let-7 has been intensively studied in roundworms and fruit flies. Although mammals have extremely similar let-7 microRNAs they seem to be more important during adulthood.

Previous studies using cells grown in the laboratory have shown that mammalian let-7 microRNAs decrease cell proliferation and cell growth. Furthermore, in mouse models of various cancers, let-7 microRNAs often reduce tumour growth when they are supplied to adult mice. Therefore, overall the let-7 group has been classified as genes that act to suppress tumors, and thus protect mice (and most likely humans too) from cancers. However, in-depth analysis of let-7 microRNAs was still missing.

Wu and Nguyen et al. have now studied mice with liver cancer using strains where they were able to regulate the levels of let-7. These mice overproduce a strong cancer-inducing gene in the liver; half were used as controls and the other half were further engineered to have moderately elevated levels of let-7 expression. Most of the control mice got large cancerous tumors, but only a few mice in the other group developed cancers and the tumors were smaller. This confirmed that let-7 hinders tumor formation.

Wu and Nguyen et al. also observed that the protected mice were less able to regenerate their liver tissues. Further experiments showed that deleting just two out of ten let-7 microRNAs enhanced the mice’s ability to regenerate liver tissue after injury. These findings indicate that let-7 microRNAs slow down the growth of both cancerous and normal cells. Lastly, when let-7 levels were raised to very high levels for a prolonged amount of time this actually led to liver damage and subsequent tumor formation.

This last observation may have important consequences for possible cancer therapies. Some scientists have shown that providing extra let-7 can slow or even reverse tumour growth, but the findings here clearly point out that too much let-7 could actually worsen the situation. Since the let-7 family comprises a handful of microRNAs in mammals, in the future it will also be important to find out to what extent these molecules play overlapping roles and how much they differ.

DOI:http://dx.doi.org/10.7554/eLife.09431.002