A Bloody Feast-Nutritional Regulation of Hematopoiesis.

Hematopoietic stem cells provide us with a lifelong supply of blood cells. Hence, their proper function is absolutely essential for life, and their dysfunction can lead to infectious and malignant diseases. These cells have specific metabolic requirements to enable their lifelong function and blood-producing capacity. With the words of the Roman poet Juvenal "a healthy mind in a healthy body" in mind, it is intriguing to understand the connection between our daily diet and the quality of our blood, with the hope that through specific dietary adjustments we can improve our hematopoietic stem cell function and prevent disease. Nowadays, dietary supplements are an expanding market filled with potential and promises for better health. However, the link between many of those supplements and human physiology is obscure. Several groups have begun to shed light on this by investigating the metabolic regulation of hematopoiesis by specific nutrients. Beyond the link to dietary supplementation, these studies have also significantly improved our understanding of basic hematopoietic stem cell biology. Herein we summarize recent knowledge on the effect of specific vitamins and amino acids, which might be considered as dietary supplements, on normal hematopoiesis and hematopoietic stem cell function. We propose that improving our understanding of the link between nutrition in general and blood physiology can ultimately lead to the optimization of health-care policies, protocols, and standards of care.

Small Nucleolar (Sno)RNA: Therapy Lays in Translation.

The ribosome is one of the largest complexes in the cell. Adding to its complexity are more than 200 RNA modification sites present on ribosomal RNAs (rRNAs) in a single human ribosome. These modifications occur in functionally important regions of the rRNA molecule, and they are vital for ribosome function and proper gene expression. Until recent technological advancements, the study of rRNA modifications and their profiles has been extremely laborious, leaving many questions unanswered. Small nucleolar RNAs (snoRNAs) are non-coding RNAs that facilitate and dictate the specificity of rRNA modification deposition, making them an attractive target for ribosome modulation. Here, we propose that through the mapping of rRNA modification profiles, we can identify cell-specific modifications with high therapeutic potential. We also describe the challenges of achieving the targeting specificity needed to implement snoRNAs as therapeutic targets in cancers.

Germline NPM1 mutations lead to altered rRNA 2'-O-methylation and cause dyskeratosis congenita.

RNA modifications are emerging as key determinants of gene expression. However, compelling genetic demonstrations of their relevance to human disease are lacking. Here, we link ribosomal RNA 2'-O-methylation (2'-O-Me) to the etiology of dyskeratosis congenita. We identify nucleophosmin (NPM1) as an essential regulator of 2'-O-Me on rRNA by directly binding C/D box small nucleolar RNAs, thereby modulating translation. We demonstrate the importance of 2'-O-Me-regulated translation for cellular growth, differentiation and hematopoietic stem cell maintenance, and show that Npm1 inactivation in adult hematopoietic stem cells results in bone marrow failure. We identify NPM1 germline mutations in patients with dyskeratosis congenita presenting with bone marrow failure and demonstrate that they are deficient in small nucleolar RNA binding. Mice harboring a dyskeratosis congenita germline Npm1 mutation recapitulate both hematological and nonhematological features of dyskeratosis congenita. Thus, our findings indicate that impaired 2'-O-Me can be etiological to human disease.

Epigenetic loss of RNA-methyltransferase NSUN5 in glioma targets ribosomes to drive a stress adaptive translational program.

Tumors have aberrant proteomes that often do not match their corresponding transcriptome profiles. One possible cause of this discrepancy is the existence of aberrant RNA modification landscapes in the so-called epitranscriptome. Here, we report that human glioma cells undergo DNA methylation-associated epigenetic silencing of NSUN5, a candidate RNA methyltransferase for 5-methylcytosine. In this setting, NSUN5 exhibits tumor-suppressor characteristics in vivo glioma models. We also found that NSUN5 loss generates an unmethylated status at the C3782 position of 28S rRNA that drives an overall depletion of protein synthesis, and leads to the emergence of an adaptive translational program for survival under conditions of cellular stress. Interestingly, NSUN5 epigenetic inactivation also renders these gliomas sensitive to bioactivatable substrates of the stress-related enzyme NQO1. Most importantly, NSUN5 epigenetic inactivation is a hallmark of glioma patients with long-term survival for this otherwise devastating disease.

An Integrated Genome-wide CRISPRa Approach to Functionalize lncRNAs in Drug Resistance.

Resistance to chemotherapy plays a significant role in cancer mortality. To identify genetic units affecting sensitivity to cytarabine, the mainstay of treatment for acute myeloid leukemia (AML), we developed a comprehensive and integrated genome-wide platform based on a dual protein-coding and non-coding integrated CRISPRa screening (DICaS). Putative resistance genes were initially identified using pharmacogenetic data from 760 human pan-cancer cell lines. Subsequently, genome scale functional characterization of both coding and long non-coding RNA (lncRNA) genes by CRISPR activation was performed. For lncRNA functional assessment, we developed a CRISPR activation of lncRNA (CaLR) strategy, targeting 14,701 lncRNA genes. Computational and functional analysis identified novel cell-cycle, survival/apoptosis, and cancer signaling genes. Furthermore, transcriptional activation of the GAS6-AS2 lncRNA, identified in our analysis, leads to hyperactivation of the GAS6/TAM pathway, a resistance mechanism in multiple cancers including AML. Thus, DICaS represents a novel and powerful approach to identify integrated coding and non-coding pathways of therapeutic relevance.

Vigilin Regulates the Expression of the Stress-Induced Ligand MICB by Interacting with Its 5' Untranslated Region.

NK cells are part of the innate immune system, and are able to identify and kill hazardous cells. The discrimination between normal and hazardous cells is possible due to an array of inhibitory and activating receptors. NKG2D is one of the prominent activating receptors expressed by all human NK cells. This receptor binds stress-induced ligands, including human MICA, MICB, and UL16-binding proteins 1-6. The interaction between NKG2D and its ligands facilitates the elimination of cells under cellular stress, such as tumor transformation. However, the mechanisms regulating the expression of these ligands are still not well understood. Under normal conditions, the NKG2D ligands were shown to be posttranscriptionally regulated by cellular microRNAs and RNA-binding proteins (RBPs). Thus far, only the 3' untranslated regions (UTRs) of MICA, MICB, and UL16-binding protein 2 were shown to be regulated by RBPs and microRNAs, usually resulting in their downregulation. In this study we investigated whether MICB expression is controlled by RBPs through its 5'UTR. We used an RNA pull-down assay followed by mass spectrometry and identified vigilin, a ubiquitously expressed multifunctional RNA-binding protein. We demonstrated that vigilin binds and negatively regulates MICB expression through its 5'UTR. Additionally, vigilin downregulation in target cells led to a significant increase in NK cell activation against said target cells. Taken together, we have discovered a novel mode of MICB regulation.

MicroRNA editing facilitates immune elimination of HCMV infected cells.

The human cytomegalovirus (HCMV) is extremely prevalent in the human population. Infection by HCMV is life threatening in immune compromised individuals and in immune competent individuals it can cause severe birth defects, developmental retardation and is even associated with tumor development. While numerous mechanisms were developed by HCMV to interfere with immune cell activity, much less is known about cellular mechanisms that operate in response to HCMV infection. Here we demonstrate that in response to HCMV infection, the expression of the short form of the RNA editing enzyme ADAR1 (ADAR1-p110) is induced. We identified the specific promoter region responsible for this induction and we show that ADAR1-p110 can edit miR-376a. Accordingly, we demonstrate that the levels of the edited-miR-376a (miR-376a(e)) increase during HCMV infection. Importantly, we show that miR-376a(e) downregulates the immune modulating molecule HLA-E and that this consequently renders HCMV infected cells susceptible to elimination by NK cells.

MiR-10b downregulates the stress-induced cell surface molecule MICB, a critical ligand for cancer cell recognition by natural killer cells.

Natural killer cells (NK) are a component of innate immunity well known for their potent ability to kill virus-infected or neoplastically transformed cells following stimulation of the NK cell receptor NKG2D. One of the various ligands of NKG2D is MICB, a stress-induced ligand that has been found to be upregulated on the surface of tumor cells. However, there is little knowledge about how this upregulation may occur or how it may be selected against in tumors as a mechanism of immune escape. Here, we report that the metastasis-associated microRNA (metastamir) miR-10b directly binds to the 3' untranslated region of MICB and downregulates its expression. Notably, antagonizing miR-10b action enhanced NKG2D-mediated killing of tumor cells in vitro and enhanced clearance of tumors in vivo. Conversely, overexpression of miR-10b downregulated MICB and impaired elimination of tumor cells. Together, our results define MICB as a novel immune target of miR-10b, implying a direct link between metastasis capability and immune escape from NK cells.

An identical miRNA of the human JC and BK polyoma viruses targets the stress-induced ligand ULBP3 to escape immune elimination.

The human polyoma viruses JCV and BKV establish asymptomatic persistent infection in 65%-90% of humans but can cause severe illness under immunosuppressive conditions. The mechanisms by which these viruses evade immune recognition are unknown. Here we show that a viral miRNA identical in sequence between JCV and BKV targets the stress-induced ligand ULBP3, which is a protein recognized by the killer receptor NKG2D. Consequently, viral miRNA-mediated ULBP3 downregulation results in reduced NKG2D-mediated killing of virus-infected cells by natural killer (NK) cells. Importantly, when the activity of the viral miRNA was inhibited during infection, NK cells killed the infected cells more efficiently. Because NKG2D is also expressed by various T cell subsets, we propose that JCV and BKV use an identical miRNA that targets ULBP3 to escape detection by both the innate and adaptive immune systems, explaining how these viruses remain latent without being eliminated by the immune system.

The human cytomegalovirus microRNA miR-UL112 acts synergistically with a cellular microRNA to escape immune elimination.

Although approximately 200 viral microRNAs are known, only very few share similar targets with their host's microRNAs. A notable example of this is the stress-induced ligand MICB, which is targeted by several distinct viral and cellular microRNAs. Through the investigation of the microRNA-mediated immune-evasion strategies of herpesviruses, we initially identified two new cellular microRNAs that targeted MICB and were expressed differently both in healthy tissues and during melanocyte transformation. We show that coexpression of various pairs of cellular microRNAs interfered with the downregulation of MICB, whereas the viral microRNAs optimized their targeting ability to efficiently downregulate MICB. Moreover, we demonstrate that through site proximity and possibly inhibition of translation, a human cytomegalovirus (HCMV) microRNA acts synergistically with a cellular microRNA to suppress MICB expression during HCMV infection.

Diverse herpesvirus microRNAs target the stress-induced immune ligand MICB to escape recognition by natural killer cells.

Herpesviruses are known for their persistent lifelong latent infection, which is made possible by their vast repertoire of immune-evasion strategies. We have previously shown that a human cytomegalovirus (HCMV) microRNA represses expression of the stress-induced Natural Killer (NK) cell ligand, MICB, to escape recognition and consequent elimination by NK cells. Here, we show functional conservation among diverse microRNAs derived from different herpesviruses, including HCMV, Kaposi's sarcoma-associated herpesvirus (KSHV), and Epstein-Barr virus (EBV), in their ability to directly target MICB mRNA and reduce its expression. Although the various viral microRNAs share no sequence homology, they are functionally similar and target MICB at different yet adjacent sites during authentic viral infection. The finding that different herpesvirus microRNAs target MICB indicates that MICB plays a pivotal role in the clash between herpesviruses and humans.