Site alpha is crucial for two routes of IFN gamma-induced MHC class I transactivation: the ISRE-mediated route and a novel pathway involving CIITA

EZH2-driven immune evasion defines high-risk pediatric AML with t(16;21) FUS::ERG gene fusion

Despite decades of research, acute myeloid leukemia (AML) remains a remarkably lethal malignancy. While pediatric AML (pAML) carries a more favorable prognosis than adult AML, the past 25 years of large clinical trials have produced few improvements in pAML survival. Nowhere is this more evident than in patients carrying a t(16;21)(p11;q22) translocation, which yields the FUS::ERG fusion transcript. Patients with FUS::ERG-positive AML are often primary refractory, and most responders quickly relapse. In COG clinical trials, allogeneic stem cell transplantation was of no benefit to FUS::ERG pAML patients; 100% of transplanted patients succumbed to their disease. Expression of major histocompatibility complex (MHC) class I & II and costimulatory molecules is absent at diagnosis in FUS::ERG AML, mirroring the epigenetic mechanism of post-transplant relapse seen in adult AML and its associated dismal outcomes. Here we show that this class-defining immune-repressive phenotype is driven by overexpression of the EZH2 histone lysine methyltransferase in vitro and in multiple clinical cohorts. We show that treatment with the FDA-approved EZH2 inhibitor tazemetostat along with IFN-γ reverses this phenotype, re-establishes MHC presentation, and severely impairs the viability of FUS::ERG AML cells. EZH2 inhibitors may thus provide the first targeted therapeutic option for patients with this high-risk subtype of pAML, with particular benefit as a bridge to successful allogeneic stem cell transplantation.

Unveiling the immunomodulatory shift: Epithelial-mesenchymal transition Alters immune mechanisms of amniotic epithelial cells

Epithelial-mesenchymal transition (EMT) changes cell phenotype by affecting immune properties of amniotic epithelial cells (AECs). The present study shows how the response to lipopolysaccharide of cells collected pre- (eAECs) and post-EMT (mAECs) induces changes in their transcriptomics profile. In fact, eAECs mainly upregulate genes involved in antigen-presenting response, whereas mAECs over-express soluble inflammatory mediator transcripts. Consistently, network analysis identifies CIITA and Nrf2 as main drivers of eAECs and mAECs immune response, respectively. As a consequence, the depletion of CIITA and Nrf2 impairs the ability of eAECs and mAECs to inhibit lymphocyte proliferation or macrophage-dependent IL-6 release, thus confirming their involvement in regulating immune response. Deciphering the mechanisms controlling the immune function of AECs pre- and post-EMT represents a step forward in understanding key physiological events wherein these cells are involved (pregnancy and labor). Moreover, controlling the immunomodulatory properties of eAECs and mAECs may be essential in developing potential strategies for regenerative medicine applications.

HLA-C dysregulation as a possible mechanism of immune evasion in SARS-CoV-2 and other RNA-virus infections

One of the mechanisms by which viruses can evade the host’s immune system is to modify the host’s DNA methylation pattern. This work aims to investigate the DNA methylation and gene expression profile of COVID-19 patients, divided into symptomatic and asymptomatic, and healthy controls, focusing on genes involved in the immune response. In this study, changes in the methylome of COVID-19 patients’ upper airways cells, the first barrier against respiratory infections and the first cells presenting viral antigens, are shown for the first time. Our results showed alterations in the methylation pattern of genes encoding proteins implicated in the response against pathogens, in particular the HLA-C gene, also important for the T-cell mediated memory response. HLA-C expression significantly decreases in COVID-19 patients, especially in those with a more severe prognosis and without other possibly confounding co-morbidities. Moreover, our bionformatic analysis revealed that the identified methylation alteration overlaps with enhancers regulating HLA-C expression, suggesting an additional mechanism exploited by SARS-CoV-2 to inhibit this fundamental player in the host’s immune response. HLA-C could therefore represent both a prognostic marker and an excellent therapeutic target, also suggesting a preventive intervention that conjugate a virus-specific antigenic stimulation with an adjuvant increasing the T-cell mediated memory response.

Class II transactivator induces expression of MHC-I and MHC-II in transmissible Tasmanian devil facial tumours

MHC-I and MHC-II molecules are critical components of antigen presentation and T cell immunity to pathogens and cancer. The two monoclonal transmissible devil facial tumours (DFT1, DFT2) exploit MHC-I pathways to overcome immunological anti-tumour and allogeneic barriers. This exploitation underpins the ongoing transmission of DFT cells across the wild Tasmanian devil population. We have previously shown that the overexpression of NLRC5 in DFT1 and DFT2 cells can regulate components of the MHC-I pathway but not MHC-II, establishing the stable upregulation of MHC-I on the cell surface. As MHC-II molecules are crucial for CD4⁺ T cell activation, MHC-II expression in tumour cells is beginning to gain traction in the field of immunotherapy and cancer vaccines. The overexpression of Class II transactivator in transfected DFT1 and DFT2 cells induced the transcription of several genes of the MHC-I and MHC-II pathways. This was further supported by the upregulation of MHC-I protein on DFT1 and DFT2 cells, but interestingly MHC-II protein was upregulated only in DFT1 cells. This new insight into the regulation of MHC-I and MHC-II pathways in cells that naturally overcome allogeneic barriers can inform vaccine, immunotherapy and tissue transplant strategies for human and veterinary medicine.

Mechanisms of MHC-I Downregulation and Role in Immunotherapy Response

Immunotherapy has become a key therapeutic strategy in the treatment of many cancers. As a result, research efforts have been aimed at understanding mechanisms of resistance to immunotherapy and how anti-tumor immune response can be therapeutically enhanced. It has been shown that tumor cell recognition by the immune system plays a key role in effective response to T cell targeting therapies in patients. One mechanism by which tumor cells can avoid immunosurveillance is through the downregulation of Major Histocompatibility Complex I (MHC-I). Downregulation of MHC-I has been described as a mechanism of intrinsic and acquired resistance to immunotherapy in patients with cancer. Depending on the mechanism, the downregulation of MHC-I can sometimes be therapeutically restored to aid in anti-tumor immunity. In this article, we will review current research in MHC-I downregulation and its impact on immunotherapy response in patients, as well as possible strategies for therapeutic upregulation of MHC-I.

Structural aspects of the MHC expression control system

The major histocompatibility complex (MHC) spans innate and adaptive immunity by presenting antigenic peptides to CD4⁺ and CD8⁺ T cells. Multiple transcription factors form an enhanceosome complex on the MHC promoter and recruit transcriptional machinery to activate gene transcription. Immune signals such as interferon-γ (IFN-γ) control MHC level by up-regulating components of the enhanceosome complex. As MHC plays crucial roles in immune regulation, alterations in the MHC enhanceosome structure will alter the pace of rapid immune responses at the transcription level and lead to various diseases related to the immune system. In this review, we discuss the current understanding of the MHC enhanceosome, with a focus on the structures of MHC enhanceosome components and the molecular basis of MHC enhanceosome assembly.

The New Kid on the Block: HLA-C, a Key Regulator of Natural Killer Cells in Viral Immunity

The human leukocyte antigen system (HLA) is a cluster of highly polymorphic genes essential for the proper function of the immune system, and it has been associated with a wide range of diseases. HLA class I molecules present intracellular host- and pathogen-derived peptides to effector cells of the immune system, inducing immune tolerance in healthy conditions or triggering effective immune responses in pathological situations. HLA-C is the most recently evolved HLA class I molecule, only present in humans and great apes. Differentiating from its older siblings, HLA-A and HLA-B, HLA-C exhibits distinctive features in its expression and interaction partners. HLA-C serves as a natural ligand for multiple members of the killer-cell immunoglobulin-like receptor (KIR) family, which are predominately expressed by natural killer (NK) cells. NK cells are crucial for the early control of viral infections and accumulating evidence indicates that interactions between HLA-C and its respective KIR receptors determine the outcome and progression of viral infections. In this review, we focus on the unique role of HLA-C in regulating NK cell functions and its consequences in the setting of viral infections.

Identification of survival-related genes and a novel gene-based prognostic signature involving the tumor microenvironment of uveal melanoma

Uveal melanoma (UM) is the most common primary intraocular malignant tumor in adults and almost fifty percent of patients subsequently develop systemic metastases usually involving the liver. The tumor microenvironment (TME) is crucial to the initiation and progression of tumors. In the present study, we comprehensively evaluated the TME of primary UM samples from The Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO) database by using several bioinformatic algorithms. The prognostic value of immune score and infiltrating immune cells in the TME were evaluated. Differentially expressed genes between the low- and high-immune score groups were also identified. The majority of tumor-infiltrating lymphocytes in UM have been determined to be activated CD8 + T cells. Therefore, weighted gene co-expression network analysis (WGCNA) was performed to identify the co-expression modules and genes significantly associated with the level of infiltrating CD8 + T cells in UM. Survival-related genes involved in the TME were identified by univariate Cox regression analysis. Furthermore, an eight-gene-based prognostic signature was established in the training dataset TCGA-UM via Lasso-penalized and multivariate Cox regression analyses. The predictive value of this signature was validated in two testing datasets. Besides, a nomogram was established to serve clinical practice. Moreover, hub genes involved in the infiltrating CD8 + T cells were identified and a potential targeted therapy for preventing metastasis of UM was proposed based on the results. In summary, our results provided a robust gene-based prognostic signature for predicting prognosis of UM patients and proposed a potential targeted therapy for preventing UM metastasis.

The MHC Class-I Transactivator NLRC5: Implications to Cancer Immunology and Potential Applications to Cancer Immunotherapy

The immune system constantly monitors the emergence of cancerous cells and eliminates them. CD8⁺ cytotoxic T lymphocytes (CTLs), which kill tumor cells and provide antitumor immunity, select their targets by recognizing tumor antigenic peptides presented by MHC class-I (MHC-I) molecules. Cancer cells circumvent immune surveillance using diverse strategies. A key mechanism of cancer immune evasion is downregulation of MHC-I and key proteins of the antigen processing and presentation machinery (APM). Even though impaired MHC-I expression in cancers is well-known, reversing the MHC-I defects remains the least advanced area of tumor immunology. The discoveries that NLRC5 is the key transcriptional activator of MHC-I and APM genes, and genetic lesions and epigenetic modifications of NLRC5 are the most common cause of MHC-I defects in cancers, have raised the hopes for restoring MHC-I expression. Here, we provide an overview of cancer immunity mediated by CD8⁺ T cells and the functions of NLRC5 in MHC-I antigen presentation pathways. We describe the impressive advances made in understanding the regulation of NLRC5 expression, the data supporting the antitumor functions of NLRC5 and a few reports that argue for a pro-tumorigenic role. Finally, we explore the possible avenues of exploiting NLRC5 for cancer immunotherapy.

The MHC Class II Transactivator CIITA: Not (Quite) the Odd-One-Out Anymore among NLR Proteins

In this review, we discuss the major histocompatibility complex (MHC) class II transactivator (CIITA), which is the master regulator of MHC class II gene expression. CIITA is the founding member of the mammalian nucleotide-binding and leucine-rich-repeat (NLR) protein family but stood apart for a long time as the only transcriptional regulator. More recently, it was found that its closest homolog, NLRC5 (NLR protein caspase activation and recruitment domain (CARD)-containing 5), is a regulator of MHC-I gene expression. Both act as non-DNA-binding activators through multiple protein-protein interactions with an MHC enhanceosome complex that binds cooperatively to a highly conserved combinatorial cis-acting module. Thus, the regulation of MHC-II expression is regulated largely through the differential expression of CIITA. In addition to the well-defined role of CIITA in MHC-II GENE regulation, we will discuss several other aspects of CIITA functions, such as its role in cancer, its role as a viral restriction element contributing to intrinsic immunity, and lastly, its very recently discovered role as an inhibitor of Ebola and SARS-Cov-2 virus replication. We will briefly touch upon the recently discovered role of NLRP3 as a transcriptional regulator, which suggests that transcriptional regulation is, after all, not such an unusual feature for NLR proteins.

NLRC5 promotes transcription of BTN3A1-3 genes and Vγ9Vδ2 T cell-mediated killing

BTN3A molecules—BTN3A1 in particular—emerged as important mediators of Vγ9Vδ2 T cell activation by phosphoantigens. These metabolites can originate from infections, e.g. with Mycobacterium tuberculosis, or by alterations in cellular metabolism. Despite the growing interest in the BTN3A genes and their high expression in immune cells and various cancers, little is known about their transcriptional regulation. Here we show that these genes are induced by NLRC5, a regulator of MHC class I gene transcription, through an atypical regulatory motif found in their promoters. Accordingly, a robust correlation between NLRC5 and BTN3A gene expression was found in healthy, in M. tuberculosis-infected donors' blood cells, and in primary tumors. Moreover, forcing NLRC5 expression promoted Vγ9Vδ2 T-cell-mediated killing of tumor cells in a BTN3A-dependent manner. Altogether, these findings indicate that NLRC5 regulates the expression of BTN3A genes and hence open opportunities to modulate antimicrobial and anticancer immunity.

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BTN3A promoters contain a unique regulatory motif occupied by overexpressed NLRC5

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NLRC5 and BTN3A mRNA levels correlate in healthy and diseased cells

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NLRC5 overexpression increases susceptibility to Vγ9Vδ2 T-cell-mediated elimination

Major histocompatibility complexes are up-regulated in glomerular endothelial cells via activation of c-Jun N-terminal kinase in 5/6 nephrectomy mice

Background and Purpose

This study aims to explore the mechanism underlying the up‐regulation of major histocompatibility complex (MHC) proteins in glomerular endothelial cells in 5/6 nephrectomy mice.

Experimental Approach

C57/BL6 mice were randomly allocated to sham‐operated (2K) and 5/6 nephrectomy (5/6Nx) groups. Mouse splenic lymphocytes, from either syngeneic or allogeneic background, were injected into 5/6Nx mice after total body irradiation. Human glomerular endothelial cells (HGECs) were cultured for experiments in vitro. Western blots, PCR, immunohistochemical and fluorescent staining were used, along with assays of tissue cytokines, lymphocyte migration and renal function.

Key Results

Four weeks after nephrectomy, expression of both mRNA and protein of MHC II, CD80, and CD86 were increased in 5/6Nx glomerular endothelial cells. After total body irradiation, 5/6Nx mice injected with lymphocytes from Balb/c mice, but not those from C57/BL6 mice, exhibited increased creatinine levels, indicating that allograft lymphocyte transfer impaired renal function. In HGECs, the protein levels of MHC and MHC Class II transactivator (CIITA) were increased by stimulation with TNF‐α or IFN‐γ, which promoted human lymphocytes movement. These increases were reduced by JNK inhibitors. In the 5/6Nx mice, JNK inhibition down‐regulated MHC II protein in glomerular endothelial cells, suggesting that JNK signalling participates in the regulation of MHC II protein.

Conclusion and Implications

Chronic inflammation in mice subjected to nephrectomy induces the up‐regulation of MHC molecules in glomerular endothelial cells. This up‐regulation is reduced by inhibition of JNK signalling.

Hepatic Stellate Cells and Hepatocytes as Liver Antigen-Presenting Cells during B. abortus Infection

In Brucellosis, the role of hepatic stellate cells (HSCs) in the induction of liver fibrosis has been elucidated recently. Here, we study how the infection modulates the antigen-presenting capacity of LX-2 cells. Brucella abortus infection induces the upregulation of class II transactivator protein (CIITA) with concomitant MHC-I and -II expression in LX-2 cells in a manner that is independent from the expression of the type 4 secretion system (T4SS). In concordance, B. abortus infection increases the phagocytic ability of LX-2 cells and induces MHC-II-restricted antigen processing and presentation. In view of the ability of B. abortus-infected LX-2 cells to produce monocyte-attracting factors, we tested the capacity of culture supernatants from B. abortus-infected monocytes on MHC-I and -II expression in LX-2 cells. Culture supernatants from B. abortus-infected monocytes do not induce MHC-I and -II expression. However, these supernatants inhibit MHC-II expression induced by IFN-γ in an IL-10 dependent mechanism. Since hepatocytes constitute the most abundant epithelial cell in the liver, experiments were conducted to determine the contribution of these cells in antigen presentation in the context of B. abortus infection. Our results indicated that B. abortus-infected hepatocytes have an increased MHC-I expression, but MHC-II levels remain at basal levels. Overall, B. abortus infection induces MHC-I and -II expression in LX-2 cells, increasing the antigen presentation. Nevertheless, this response could be modulated by resident or infiltrating monocytes/macrophages.

Characterization of HLA-G Regulation and HLA Expression in Breast Cancer and Malignant Melanoma Cell Lines upon IFN-γ Stimulation and Inhibition of DNA Methylation

The potential role of human leukocyte antigen (HLA)-G as a target for new cancer immunotherapy drugs has increased the interest in the analysis of mechanisms by which HLA-G expression is regulated, and how the expression can be manipulated. We characterized HLA expression in breast cancer and malignant melanoma cell lines and investigated the induction of HLA-G expression by two distinct mechanisms: stimulation with interferon (IFN)-γ or inhibition of methylation by treatment with 5-aza-2'-deoxycytidine (5-aza-dC). The effect of IFN-γ and 5-aza-dC on HLA expression was dependent on the cancer cell lines studied. However, in general, surface expression of HLA class Ia was induced on all cell lines. Surface expression of HLA-G was inconclusive but induction of HLA-G mRNA was prevalent upon treatment with 5-aza-dC and a combination of IFN-γ and 5-aza-dC. IFN-γ alone failed to induce HLA-G expression in the HLA-G-negative cell lines. The results support that HLA-G expression is regulated partly by DNA methylation. Furthermore, IFN-γ may play a role in the maintenance of HLA-G expression rather than inducing expression. The study demonstrates the feasibility of manipulating HLA expression and contributes to the exploration of mechanisms that can be potential targets for immunotherapy in breast cancer and malignant melanoma.

miR-19 regulates the expression of interferon-induced genes and MHC class I genes in human cancer cells

MicroRNA-19 (miR-19) is identified as the key oncogenic component of the miR-17-92 cluster. When we explored the functions of the dysregulated miR-19 in lung cancer, microarray-based data unexpectedly demonstrated that some immune and inflammatory response genes (i.e., IL32, IFI6 and IFIT1) were generally down-regulated by miR-19 overexpression in A549 cells, which prompted us to fully investigate whether the miR-19 family (i.e., miR-19a and miR-19b-1) was implicated in regulating the expression of immune and inflammatory response genes in cancer cells. In the present study, we observed that miR-19a or miR-19b-1 overexpression by miRNA mimics in the A549, HCC827 and CNE2 cells significantly downregulated the expression of interferon (IFN)-regulated genes (i.e., IRF7, IFI6, IFIT1, IFITM1, IFI27 and IFI44L). Furthermore, the ectopic miR-19a or miR-19b-1 expression in the A549, HCC827, CNE2 and HONE1 cells led to a general downward trend in the expression profile of major histocompatibility complex (MHC) class I genes (such as HLA-B, HLA-E, HLA-F or HLA-G); conversely, miR-19a or miR-19b-1 inhibition by the miRNA inhibitor upregulated the aforementioned MHC Class I gene expression, suggesting that miR-19a or miR-19b-1 negatively modulates MHC Class I gene expression. The miR-19a or miR-19b-1 mimics reduced the expression of interleukin (IL)-related genes (i.e., IL1B, IL11RA and IL6) in the A549, HCC827, CNE2 or HONE1 cells. The ectopic expression of miR-19a or miR-19b-1 downregulated IL32 expression in the A549 and HCC827 cells and upregulated IL32 expression in CNE2 and HONE1 cells. In addition, enforced miR-19a or miR-19b-1 expression suppressed IL-6 production by lung cancer and nasopharyngeal carcinoma (NPC) cells. Taken together, these findings demonstrate, for the first time, that miR-19 can modulate the expression of IFN-induced genes and MHC class I genes in human cancer cells, suggesting a novel role of miR-19 in linking inflammation and cancer, which remains to be fully characterized.

Complete loss of the MHC II pathway in an anglerfish, Lophius piscatorius

Genome studies in fish provide evidence for the adaptability of the vertebrate immune system, revealing alternative immune strategies. The reported absence of the major compatibility complex (MHC) class II pathway components in certain species of pipefish (genus Syngnathus) and cod-like fishes (order Gadiformes) is of particular interest. The MHC II pathway is responsible for immunization and defence against extracellular threats through the presentation of exogenous peptides to T helper cells. Here, we demonstrate the absence of all genes encoding MHC II components (CD4, CD74 A/B, and both classical and non-classical MHC II α/β) in the genome of an anglerfish, Lophius piscatorius, indicating loss of the MHC II pathway. By contrast, it has previously been reported that another anglerfish, Antennarius striatus, retains all MHC II genes, placing the loss of MHC II in the Lophius clade to their most recent common ancestor. In the three taxa where MHC II loss has occurred, the gene loss has been restricted to four or five core MHC II components, suggesting that, in teleosts, only these genes have functions that are restricted to the MHC II pathway.

Tumor-induced escape mechanisms and their association with resistance to checkpoint inhibitor therapy

Immunotherapy aims to activate the immune system to fight cancer in a very specific and targeted manner. Despite the success of different immunotherapeutic strategies, in particular antibodies directed against checkpoints as well as adoptive T-cell therapy, the response of patients is limited in different types of cancers. This attributes to escape of the tumor from immune surveillance and development of acquired resistances during therapy. In this review, the different evasion and resistance mechanisms that limit the efficacy of immunotherapies targeting tumor-associated antigens presented by major histocompatibility complex molecules on the surface of the malignant cells are summarized. Overcoming these escape mechanisms is a great challenge, but might lead to a better clinical outcome of patients and is therefore currently a major focus of research.

Long Noncoding RNA HCP5, a Hybrid HLA Class I Endogenous Retroviral Gene: Structure, Expression, and Disease Associations

The HCP5 RNA gene (NCBI ID: 10866) is located centromeric of the HLA-B gene and between the MICA and MICB genes within the major histocompatibility complex (MHC) class I region. It is a human species-specific gene that codes for a long noncoding RNA (lncRNA), composed mostly of an ancient ancestral endogenous antisense 3′ long terminal repeat (LTR, and part of the internal pol antisense sequence of endogenous retrovirus (ERV) type 16 linked to a human leukocyte antigen (HLA) class I promoter and leader sequence at the 5′-end. Since its discovery in 1993, many disease association and gene expression studies have shown that HCP5 is a regulatory lncRNA involved in adaptive and innate immune responses and associated with the promotion of some autoimmune diseases and cancers. The gene sequence acts as a genomic anchor point for binding transcription factors, enhancers, and chromatin remodeling enzymes in the regulation of transcription and chromatin folding. The HCP5 antisense retroviral transcript also interacts with regulatory microRNA and immune and cellular checkpoints in cancers suggesting its potential as a drug target for novel antitumor therapeutics.

Immunoepigenetics Combination Therapies: An Overview of the Role of HDACs in Cancer Immunotherapy

Long-standing efforts to identify the multifaceted roles of histone deacetylase inhibitors (HDACis) have positioned these agents as promising drug candidates in combatting cancer, autoimmune, neurodegenerative, and infectious diseases. The same has also encouraged the evaluation of multiple HDACi candidates in preclinical studies in cancer and other diseases as well as the FDA-approval towards clinical use for specific agents. In this review, we have discussed how the efficacy of immunotherapy can be leveraged by combining it with HDACis. We have also included a brief overview of the classification of HDACis as well as their various roles in physiological and pathophysiological scenarios to target key cellular processes promoting the initiation, establishment, and progression of cancer. Given the critical role of the tumor microenvironment (TME) towards the outcome of anticancer therapies, we have also discussed the effect of HDACis on different components of the TME. We then have gradually progressed into examples of specific pan-HDACis, class I HDACi, and selective HDACis that either have been incorporated into clinical trials or show promising preclinical effects for future consideration. Finally, we have included examples of ongoing trials for each of the above categories of HDACis as standalone agents or in combination with immunotherapeutic approaches.

Biological Consequences of MHC-II Expression by Tumor Cells in Cancer

Immunotherapy has emerged as a key pillar of cancer treatment. To build upon the recent successes of immunotherapy, intense research efforts are aimed at a molecular understanding of antitumor immune responses, identification of biomarkers of immunotherapy response and resistance, and novel strategies to circumvent resistance. These studies are revealing new insight into the intricacies of tumor cell recognition by the immune system, in large part through MHCs. Although tumor cells widely express MHC-I, a subset of tumors originating from a variety of tissues also express MHC-II, an antigen-presenting complex traditionally associated with professional antigen-presenting cells. MHC-II is critical for antigen presentation to CD4+ T lymphocytes, whose role in antitumor immunity is becoming increasingly appreciated. Accumulating evidence demonstrates that tumor-specific MHC-II associates with favorable outcomes in patients with cancer, including those treated with immunotherapies, and with tumor rejection in murine models. Herein, we will review current research regarding tumor-enriched MHC-II expression and regulation in a range of human tumors and murine models, and the possible therapeutic applications of tumor-specific MHC-II.

Class I transactivator, NLRC5: a central player in the MHC class I pathway and cancer immune surveillance

Major histocompatibility complex (MHC) class I and class II molecules play critical roles in the activation of the adaptive immune system by presenting antigens to CD8+ and CD4+ T cells, respectively. Although it has been well known that CIITA (MHC class II transactivator), an NLR (nucleotide-binding domain, leucine-rich-repeat containing) protein, as a master regulator of MHC class II gene expression, the mechanism of MHC class I gene transactivation was unclear. Recently, another NLR protein, NLRC5 (NLR family, CARD domain-containing 5), was identified as an MHC class I transactivator (CITA). NLRC5 is a critical regulator for the transcriptional activation of MHC class I genes and other genes involved in the MHC class I antigen presentation pathway. CITA/NLRC5 plays a crucial role in human cancer immunity through the recruitment and activation of tumor killing CD8+ T cells. Here, we discuss the molecular function and mechanism of CITA/NLRC5 in the MHC class I pathway and its role in cancer.

The antitumor effects of entinostat in ovarian cancer require adaptive immunity

BACKGROUND

Ovarian cancer is poorly immunogenic; however, increased major histocompatibility complex class II (MHCII) expression correlates with improved immune response and prolonged survival in patients with ovarian cancer. The authors previously demonstrated that the histone deacetylase inhibitor entinostat increases MHCII expression on ovarian cancer cells. In the current study, they evaluated whether entinostat treatment and resultant MHCII expression would enhance beneficial immune responses and impair tumor growth in mice with ovarian cancer.

METHODS

C57BL/6 mice bearing intraperitoneal ID8 tumors were randomized to receive entinostat 20 mg/kg daily versus control. Changes in messenger RNA (mRNA) expression of 46 genes important for antitumor immunity were evaluated using NanoString analysis, and multicolor flow cytometry was used to measure changes in protein expression and tumor-infiltrating immune cells.

RESULTS

Entinostat treatment decreased the growth of both subcutaneously and omental ID8 tumors and prolonged survival in immunocompetent C57BL/6 mice. NanoString analysis revealed significant changes in mRNA expression in 21 of 46 genes, including increased expression of the MHCI pathway, the MHCII transactivator (CIITA), interferon γ, and granzyme B. C57BL/6 mice that received entinostat had increased MHCII expression on omental tumor cells and a higher frequency of tumor-infiltrating, CD8-positive T cells by flow cytometry. In immunocompromised mice, treatment with entinostat had no effect on tumor size and did not increase MHCII expression.

CONCLUSIONS

In the current murine ovarian cancer model, entinostat treatment enhances beneficial immune responses. Moreover, these antitumor effects of entinostat are dependent on an intact immune system. Future studies combining entinostat with checkpoint inhibitors or other immunomodulatory agents may achieve more durable antitumor responses in patients with ovarian cancer.

Molecular evolution of elements controlling HLA-C expression: Adaptation to a role as a killer-cell immunoglobulin-like receptor ligand regulating natural killer cell function

The regulatory elements controlling the transcription of the HLA-A, HLA-B, and HLA-C genes have been extensively studied and compared. However, few studies have considered regulatory differences in the HLA genes from the perspective of their role as ligands for the killer-cell immunoglobulin-like receptor (KIR) family of HLA receptors expressed by natural killer (NK) cells. HLA-C is the most recently evolved gene, and there is considerable evidence pointing to its emergence as a specialized KIR ligand playing a major role in the missing-self recognition system of NK cells. Here I evaluate gene-specific differences in regulatory elements of the HLA genes, showing alterations that are consistent with the adaptation of HLA-C to a role in NK cell regulation.

Chemical and genetic control of IFNγ-induced MHCII expression

The cytokine interferon-γ (IFNγ) can induce expression of MHC class II (MHCII) on many different cell types, leading to antigen presentation to CD4⁺ T cells and immune activation. This has also been linked to anti-tumour immunity and graft-versus-host disease. The extent of MHCII upregulation by IFNγ is cell type-dependent and under extensive control of epigenetic regulators and signalling pathways. Here, we identify novel genetic and chemical factors that control this form of MHCII expression. Loss of the oxidative stress sensor Keap1, autophagy adaptor p62/SQSTM1, ubiquitin E3-ligase Cullin-3 and chromatin remodeller BPTF impair IFNγ-mediated MHCII expression. A similar phenotype is observed for arsenite, an oxidative stressor. Effects of the latter can be reversed by the inhibition of HDAC1/2, linking oxidative stress conditions to epigenetic control of MHCII expression. Furthermore, dimethyl fumarate, an antioxidant used for the treatment of several autoimmune diseases, impairs the IFNγ response by manipulating transcriptional control of MHCII We describe novel pathways and drugs related to oxidative conditions in cells impacting on IFNγ-mediated MHCII expression, which provide a molecular basis for the understanding of MHCII-associated diseases.

Evolutionary Convergence and Divergence in NLR Function and Structure

The recognition of cellular damage caused by either pathogens or abiotic stress is essential for host defense in all forms of life in the plant and animal kingdoms. The NOD-like receptors (NLRs) represent a large family of multidomain proteins that were initially discovered for their role in host defense in plants and vertebrates. Over recent years the wide distribution of NLRs among metazoans has become apparent and their origins have begun to emerge. Moreover, intense study of NLR function has shown that they play essential roles beyond pathogen recognition - in the regulation of antigen presentation, cell death, inflammation, and even in embryonic development. We summarize here the latest insights into NLR biology and discuss examples of converging and diverging evolution of NLR function and structure.

NLRC5/CITA: A Key Player in Cancer Immune Surveillance

Cancer cells need to escape immune surveillance for successful tumor growth. Loss of MHC class I has been described as a major immune evasion strategy in many cancers. MHC class I transactivator (CITA), NLRC5 [nucleotide-binding domain and leucine-rich repeats containing (NLR) family, caspase activation and recruitment domain (CARD) domain containing 5], is a key transcription coactivator of MHC class I genes. Recent genetic studies have revealed that NLRC5 is a major target for cancer immune evasion mechanisms. The reduced expression or activity of NLRC5 caused by promoter methylation, copy number loss, or somatic mutations is associated with defective MHC class I expression, impaired cytotoxic T cell activation, and poor patient prognosis. Here, we review the role of NLRC5 in cancer immune evasion and the future prospects for cancer research.

NF-Y and the immune response: Dissecting the complex regulation of MHC genes

Nuclear Factor Y (NF-Y) was first described as one of the CCAAT binding factors. Although CCAAT motifs were found to be present in various genes, NF-Y attracted a lot of interest early on, due to its role in Major Histocompatibility Complex (MHC) gene regulation. MHC genes are crucial in immune response and show peculiar expression patterns. Among other conserved elements on MHC promoters, an NF-Y binding CCAAT box was found to contribute to MHC transcriptional regulation. NF-Y along with other DNA binding factors assembles in a stereospecific manner to form a multiprotein scaffold, the MHC enhanceosome, which is necessary but not sufficient to drive transcription. Transcriptional activation is achieved by the recruitment of yet another factor, the class II transcriptional activator (CIITA). In this review, we briefly discuss basic findings on MHCII transcription regulation and we highlight NF-Y different modes of function in MHCII gene activation. This article is part of a Special Issue entitled: Nuclear Factor Y in Development and Disease, edited by Prof. Roberto Mantovani.

Upregulation of HLA Expression in Primary Uveal Melanoma by Infiltrating Leukocytes

Introduction

Uveal melanoma (UM) with an inflammatory phenotype, characterized by infiltrating leukocytes and increased human leukocyte antigen (HLA) expression, carry an increased risk of death due to metastases. These tumors should be ideal for T-cell based therapies, yet it is not clear why prognostically-infaust tumors have a high HLA expression. We set out to determine whether the level of HLA molecules in UM is associated with other genetic factors, HLA transcriptional regulators, or microenvironmental factors.

Methods

28 enucleated UM were used to study HLA class I and II expression, and several regulators of HLA by immunohistochemistry, PCR microarray, qPCR and chromosome SNP-array. Fresh tumor samples of eight primary UM and four metastases were compared to their corresponding xenograft in SCID mice, using a PCR microarray and SNP array.

Results

Increased expression levels of HLA class I and II showed no dosage effect of chromosome 6p, but, as expected, were associated with monosomy of chromosome 3. Increased HLA class I and II protein levels were positively associated with their gene expression and with raised levels of the peptide-loading gene TAP1, and HLA transcriptional regulators IRF1, IRF8, CIITA, and NLRC5, revealing a higher transcriptional activity in prognostically-bad tumors. Implantation of fresh human tumor samples into SCID mice led to a loss of infiltrating leukocytes, and to a decreased expression of HLA class I and II genes, and their regulators.

Conclusion

Our data provides evidence for a proper functioning HLA regulatory system in UM, offering a target for T-cell based therapies.

CITA/NLRC5: A critical transcriptional regulator of MHC class I gene expression

Major histocompatibility complex (MHC) class I and class II molecules play essential roles in the development and activation of the human adaptive immune system. An NLR protein, CIITA (MHC class II transactivator) has been recognized as a master regulator of MHC class II gene expression, albeit knowledge about the regulatory mechanism of MHC class I gene expression had been limited. Recently identified MHC class I transactivator (CITA), or NLRC5, also belongs to the NLR protein family and constitutes a critical regulator for the transcriptional activation of MHC class I genes. In addition to MHC class I genes, CITA/NLRC5 induces the expression of β2 -microglobulin, TAP1 and LMP2, essential components of the MHC class I antigen presentation pathway. Therefore, CITA/NLRC5 and CIITA are transcriptional regulators that orchestrate the concerted expression of critical components in the MHC class I and class II pathways, respectively. © 2016 BioFactors, 42(4):349-357, 2016.

Role of EZH2 histone methyltrasferase in melanoma progression and metastasis

There is accumulating evidence that the histone methyltransferase enhancer of zeste homolog 2 (EZH2), the main component of the polycomb-repressive complex 2 (PRC2), is involved in melanoma progression and metastasis. Novel drugs that target and reverse such epigenetic changes may find a way into the management of patients with advanced melanoma. We provide a comprehensive up-to-date review of the role and biology of EZH2 on gene transcription, senescence/apoptosis, melanoma microenvironment, melanocyte stem cells, the immune system, and micro RNA. Furthermore, we discuss EZH2 inhibitors as potential anti-cancer therapy.

NLRC5/MHC class I transactivator is a target for immune evasion in cancer

Cancer cells develop under immune surveillance, thus necessitating immune escape for successful growth. Loss of MHC class I expression provides a key immune evasion strategy in many cancers, although the molecular mechanisms remain elusive. MHC class I transactivator (CITA), known as "NLRC5" [NOD-like receptor (NLR) family, caspase recruitment (CARD) domain containing 5], has recently been identified as a critical transcriptional coactivator of MHC class I gene expression. Here we show that the MHC class I transactivation pathway mediated by CITA/NLRC5 constitutes a target for cancer immune evasion. In all the 21 tumor types we examined, NLRC5 expression was highly correlated with the expression of MHC class I, with cytotoxic T-cell markers, and with genes in the MHC class I antigen-presentation pathway, including LMP2/LMP7, TAP1, and β2-microglobulin. Epigenetic and genetic alterations in cancers, including promoter methylation, copy number loss, and somatic mutations, were most prevalent in NLRC5 among all MHC class I-related genes and were associated with the impaired expression of components of the MHC class I pathway. Strikingly, NLRC5 expression was significantly associated with the activation of CD8(+) cytotoxic T cells and patient survival in multiple cancer types. Thus, NLRC5 constitutes a novel prognostic biomarker and potential therapeutic target of cancers.

Identification of a nuclear export sequence in the MHC CIITA

Initiation of an immune response through expression of MHC class II and related genes is under the control of the CIITA. Normally found in both the cytoplasm and nucleus, CIITA is tightly controlled by a variety of posttranslational modifications as well as interactions with other nuclear and cytoplasmic factors, whereas disruption of this dual subcellular localization impairs CIITA functioning and expression of target genes. Although CIITA has well-defined domains necessary for its nuclear import, the region responsible for the translocation of CIITA from the nucleus has not been characterized. In this study, we identify a leucine-rich motif at residues 717-724 that bears strong homology to known nuclear export sequence (NES) domains. Mutation of this region renders CIITA insensitive to treatment with leptomycin B, an inhibitor of nuclear export, whereas fusion of this domain to a heterologous GFP is sufficient to induce its export to the cytoplasm or cause its retention in the nucleus following leptomycin B treatment. Point mutations of specific leucine residues within the NES disrupt the normal subcellular distribution of the full-length CIITA, impair its ability to interact with the nuclear export factor CRM1, and enhance CIITA-induced gene expression from an MHC class II gene promoter. IFN-γ stimulation of class II genes is further enhanced by inhibiting the nuclear export of endogenous CIITA. Collectively, these data demonstrate the first identification of a specific NES within CIITA and place it among the other protein domains that contribute to the posttranslational regulation of CIITA activity.

Insights into HLA-G Genetics Provided by Worldwide Haplotype Diversity

Human leukocyte antigen G (HLA-G) belongs to the family of non-classical HLA class I genes, located within the major histocompatibility complex (MHC). HLA-G has been the target of most recent research regarding the function of class I non-classical genes. The main features that distinguish HLA-G from classical class I genes are (a) limited protein variability, (b) alternative splicing generating several membrane bound and soluble isoforms, (c) short cytoplasmic tail, (d) modulation of immune response (immune tolerance), and (e) restricted expression to certain tissues. In the present work, we describe the HLA-G gene structure and address the HLA-G variability and haplotype diversity among several populations around the world, considering each of its major segments [promoter, coding, and 3′ untranslated region (UTR)]. For this purpose, we developed a pipeline to reevaluate the 1000Genomes data and recover miscalled or missing genotypes and haplotypes. It became clear that the overall structure of the HLA-G molecule has been maintained during the evolutionary process and that most of the variation sites found in the HLA-G coding region are either coding synonymous or intronic mutations. In addition, only a few frequent and divergent extended haplotypes are found when the promoter, coding, and 3′UTRs are evaluated together. The divergence is particularly evident for the regulatory regions. The population comparisons confirmed that most of the HLA-G variability has originated before human dispersion from Africa and that the allele and haplotype frequencies have probably been shaped by strong selective pressures.

Temporal gene profiling of the 5XFAD transgenic mouse model highlights the importance of microglial activation in Alzheimer's disease

BACKGROUND

The 5XFAD early onset mouse model of Alzheimer's disease (AD) is gaining momentum. Behavioral, electrophysiological and anatomical studies have identified age-dependent alterations that can be reminiscent of human AD. However, transcriptional changes during disease progression have not yet been investigated. To this end, we carried out a transcriptomic analysis on RNAs from the neocortex and the hippocampus of 5XFAD female mice at the ages of one, four, six and nine months (M1, M4, M6, M9).

RESULTS

Our results show a clear shift in gene expression patterns between M1 and M4. At M1, 5XFAD animals exhibit region-specific variations in gene expression patterns whereas M4 to M9 mice share a larger proportion of differentially expressed genes (DEGs) that are common to both regions. Analysis of DEGs from M4 to M9 underlines the predominance of inflammatory and immune processes in this AD mouse model. The rise in inflammation, sustained by the overexpression of genes from the complement and integrin families, is accompanied by an increased expression of transcripts involved in the NADPH oxidase complex, phagocytic processes and IFN-γ related pathways.

CONCLUSIONS

Overall, our data suggest that, from M4 to M9, sustained microglial activation becomes the predominant feature and point out that both detrimental and neuroprotective mechanisms appear to be at play in this model. Furthermore, our study identifies a number of genes already known to be altered in human AD, thus confirming the use of the 5XFAD strain as a valid model for understanding AD pathogenesis and for screening potential therapeutic molecules.

Transcriptional and posttranscriptional regulations of the HLA-G gene

HLA-G has a relevant role in immune response regulation. The overall structure of the HLA-G coding region has been maintained during the evolution process, in which most of its variable sites are synonymous mutations or coincide with introns, preserving major functional HLA-G properties. The HLA-G promoter region is different from the classical class I promoters, mainly because (i) it lacks regulatory responsive elements for IFN-γ and NF-κB, (ii) the proximal promoter region (within 200 bases from the first translated ATG) does not mediate transactivation by the principal HLA class I transactivation mechanisms, and (iii) the presence of identified alternative regulatory elements (heat shock, progesterone and hypoxia-responsive elements) and unidentified responsive elements for IL-10, glucocorticoids, and other transcription factors is evident. At least three variable sites in the 3' untranslated region have been studied that may influence HLA-G expression by modifying mRNA stability or microRNA binding sites, including the 14-base pair insertion/deletion, +3142C/G and +3187A/G polymorphisms. Other polymorphic sites have been described, but there are no functional studies on them. The HLA-G coding region polymorphisms might influence isoform production and at least two null alleles with premature stop codons have been described. We reviewed the structure of the HLA-G promoter region and its implication in transcriptional gene control, the structure of the HLA-G 3'UTR and the major actors of the posttranscriptional gene control, and, finally, the presence of regulatory elements in the coding region.

NLRC5, at the Heart of Antigen Presentation

Nucleotide-binding domain and leucine-rich repeat containing receptors (NLRs) are intracellular proteins mainly involved in pathogen recognition, inflammatory responses, and cell death. Until recently, the function of the family member NLR caspase recruitment domain (CARD) containing 5 (NLRC5) has been a matter of debate. It is now clear that NLRC5 acts as a transcriptional regulator of the major-histocompatibility complex class I. In this review we detail the development of our understanding of NLRC5 function, discussing both the accepted and the controversial aspects of NLRC5 activity. We give insight into the molecular mechanisms, and the potential implications, of NLRC5 function in health and disease.

Human dominant-negative class II transactivator transgenic pigs - effect on the human anti-pig T-cell immune response and immune status

Swine leucocyte antigen (SLA) class II molecules on porcine (p) cells play a crucial role in xenotransplantation as activators of recipient human CD4(+) T cells. A human dominant-negative mutant class II transactivator (CIITA-DN) transgene under a CAG promoter with an endothelium-specific Tie2 enhancer was constructed. CIITA-DN transgenic pigs were produced by nuclear transfer/embryo transfer. CIITA-DN pig cells were evaluated for expression of SLA class II with/without activation, and the human CD4(+) T-cell response to cells from CIITA-DN and wild-type (WT) pigs was compared. Lymphocyte subset numbers and T-cell function in CIITA-DN pigs were compared with those in WT pigs. The expression of SLA class II on antigen-presenting cells from CIITA-DN pigs was significantly reduced (40-50% reduction compared with WT; P < 0·01), and was completely suppressed on aortic endothelial cells (AECs) even after activation (100% suppression; P < 0·01). The human CD4(+) T-cell response to CIITA-DN pAECs was significantly weaker than to WT pAECs (60-80% suppression; P < 0·01). Although there was a significantly lower frequency of CD4(+) cells in the PBMCs from CIITA-DN (20%) than from WT (30%) pigs (P < 0·01), T-cell proliferation was similar, suggesting no significant immunological compromise. Organs and cells from CIITA-DN pigs should be partially protected from the human cellular immune response.

Analysis of the genomic response of human prostate cancer cells to histone deacetylase inhibitors

Histone deacetylases (HDACs) have emerged as important targets for cancer treatment. HDAC-inhibitors (HDACis) are well tolerated in patients and have been approved for the treatment of patients with cutaneous T-cell lymphoma (CTCL). To improve the clinical benefit of HDACis in solid tumors, combination strategies with HDACis could be employed. In this study, we applied Analysis of Functional Annotation (AFA) to provide a comprehensive list of genes and pathways affected upon HDACi-treatment in prostate cancer cells. This approach provides an unbiased and objective approach to high throughput data mining. By performing AFA on gene expression data from prostate cancer cell lines DU-145 (an HDACi-sensitive cell line) and PC3 (a relatively HDACi-resistant cell line) treated with HDACis valproic acid or vorinostat, we identified biological processes that are affected by HDACis and are therefore potential treatment targets for combination therapy. Our analysis revealed that HDAC-inhibition resulted among others in upregulation of major histocompatibility complex (MHC) genes and deregulation of the mitotic spindle checkpoint by downregulation of genes involved in mitosis. These findings were confirmed by AFA on publicly available data sets from HDACi-treated prostate cancer cells. In total, we analyzed 375 microarrays with HDACi treated and non-treated (control) prostate cancer cells. All results from this extensive analysis are provided as an online research source (available at the journal's website and at http://luigimarchionni.org/HDACIs.html). By publishing this data, we aim to enhance our understanding of the cellular changes after HDAC-inhibition, and to identify novel potential combination strategies with HDACis for the treatment of prostate cancer patients.

Tumor necrosis factor α-induced hypoxia-inducible factor 1α-β-catenin axis regulates major histocompatibility complex class I gene activation through chromatin remodeling

Hypoxia-inducible factor 1α (HIF-1α) plays a crucial role in the progression of glioblastoma multiforme tumors, which are characterized by their effective immune escape mechanisms. As major histocompatibility complex class I (MHC-I) is involved in glioma immune evasion and since HIF-1α is a pivotal link between inflammation and glioma progression, the role of tumor necrosis factor alpha (TNF-α)-induced inflammation in MHC-I gene regulation was investigated. A TNF-α-induced increase in MHC-I expression and transcriptional activation was concurrent with increased HIF-1α, ΝF-κΒ, and β-catenin activities. While knockdown of HIF-1α and β-catenin abrogated TNF-α-induced MHC-I activation, NF-κB had no effect. β-Catenin inhibition abrogated HIF-1α activation and vice versa, and this HIF-1α-β-catenin axis positively regulated CREB phosphorylation. Increased CREB activation was accompanied by its increased association with β-catenin and CBP. Chromatin immunoprecipitation revealed increased CREB enrichment at CRE/site α on the MHC-I promoter in a β-catenin-dependent manner. β-Catenin replaced human Brahma (hBrm) with Brg1 as the binding partner for CREB at the CRE site. The hBrm-to-Brg1 switch is crucial for MHC-I regulation, as ATPase-deficient Brg1 abolished TNF-α-induced MHC-I expression. β-Catenin also increased the association of MHC-I enhanceosome components RFX5 and NF-YB at the SXY module. CREB acts as a platform for assembling coactivators and chromatin remodelers required for MHC-I activation in a HIF-1α/β-catenin-dependent manner.

Interferon induced IFIT family genes in host antiviral defense

Secretion of interferons (IFNs) from virus-infected cells is a hallmark of host antiviral immunity and in fact, IFNs exert their antiviral activities through the induction of antiviral proteins. The IFN-induced protein with tetratricopeptide repeats (IFITs) family is among hundreds of IFN-stimulated genes. This family contains a cluster of duplicated loci. Most mammals have IFIT1, IFIT2, IFIT3 and IFIT5; however, bird, marsupial, frog and fish have only IFIT5. Regardless of species, IFIT5 is always adjacent to SLC16A12. IFIT family genes are predominantly induced by type I and type III interferons and are regulated by the pattern recognition and the JAK-STAT signaling pathway. IFIT family proteins are involved in many processes in response to viral infection. However, some viruses can escape the antiviral functions of the IFIT family by suppressing IFIT family genes expression or methylation of 5' cap of viral molecules. In addition, the variants of IFIT family genes could significantly influence the outcome of hepatitis C virus (HCV) therapy. We believe that our current review provides a comprehensive picture for the community to understand the structure and function of IFIT family genes in response to pathogens in human, as well as in animals.

NLRC5: a key regulator of MHC class I-dependent immune responses

The expression of MHC class I molecules is crucial for the initiation and regulation of adaptive immune responses against pathogens. NOD-, LRR- and CARD-containing 5 (NLRC5) was recently identified as a specific transactivator of MHC class I genes (CITA). NLRC5 and the master regulator for MHC class II genes, class II transactivator (CIITA), interact with similar MHC promoter-bound factors. Here, we provide a broad overview of the molecular mechanisms behind MHC class I transcription and the role of the class I transactivator NLRC5 in MHC class I-dependent immune responses.

Considerations on regulatory sequences of the distal promoter region of the HLA-G gene

Gene expression in eukaryotic cells is accomplished via association of transcription factors, some of which directly bind to DNA regulatory sequences. HLA-G codes for an immunoregulatory protein with tissue-specific expression, its unique promoter regulatory region is responsible for this feature. The aim of the present study was to explore motif composition as well as identify haplotypes in the HLA-G 5' distal promoter region. The sample was composed by 176 euro-descendents individuals genotyped by Sequence Based Typing of HLA-G distal promoter, encompassing 16 SNPs. Haplotypes were inferred by the expectation maximization algorithm. Only haplotypes with frequency higher than 1% were aligned to check for similarities and differences and thirteen haplotypes remained. For a better understanding of the nucleotide diversity of the analyzed region our approach was to split the whole sequence into two regions. Two contrasting haplotype groups were found in both regions, allowing us to suggest the existence of different transcription factors capable of binding cis elements while the intra-group variations suggest the intensity modulation of binding with regulatory factors.

NF-κB-mediated inverse regulation of fractalkine and CX3CR1 during CLP-induced sepsis

Fractalkine is a unique member of the CX3C chemokine family by unfolding its potential through the chemokine (C-X3-C motif) receptor 1 (CX3CR1) with dual function acting both as an adhesion molecule and a soluble chemokine. The regulation of this chemokine is still not clear. Therefore, we were interested in the regulation of fractalkine and of CX3CR1 in experimental sepsis. In addition, we investigated the role of NF-κB for the regulation of fractalkine and of CX3CR1. Using a mouse model of cecal ligation and puncture (CLP)-induced sepsis, we found elevated fractalkine mRNA levels in the heart, lung, kidney, and liver, as well as increased plasma levels 24 and 48h after CLP, respectively. In parallel, CLP resulted in a significant downregulation of CX3CR1 mRNA receptor expression in all investigated murine tissues. Septic mice that were pretreated with the selective NF-κB inhibitor pyrrolidine dithiocarbamate (PDTC) were found to have a decreased liberation of proinflammtory cytokines such as TNF-α, IL-1β, IL-6, or IFN-γ. Further PDTC pretreatment attenuated CLP-induced downregulation of CX3CR1 mRNA as well as CLP-induced upregulation of fractalkine mRNA expression in the heart, lung, kidney, liver, and the increase in fractalkine plasma levels of septic mice. In addition, CLP-induced downregulation of renal CX3CR1 protein expression was inhibited by PDTC-pretreatment. Taken together, our data indicate a CLP-induced inverse regulation of the expression between the relating ligand and the receptor with an upregulation of fractalkine and downregulation of CX3CR1, which seems to be mediated by the transcripting factor NF-κB likely via reduced liberation of proinflammtory cytokines in the whole murine organism.

Cutting edge: impaired MHC class I expression in mice deficient for Nlrc5/class I transactivator

MHC class I and class II are crucial for the adaptive immune system. Although regulation of MHC class II expression by CIITA has long been recognized, the mechanism of MHC class I transactivation has been largely unknown until the recent discovery of NLRC5/class I transactivator. In this study, we show using Nlrc5-deficient mice that NLRC5 is required for both constitutive and inducible MHC class I expression. Loss of Nlrc5 resulted in severe reduction in the expression of MHC class I and related genes such as β(2)-microglobulin, Tap1, or Lmp2, but did not affect MHC class II levels. IFN-γ stimulation could not overcome the impaired MHC class I expression in Nlrc5-deficient cells. Upon infection with Listeria monocyogenes, Nlrc5-deficient mice displayed impaired CD8(+) T cell activation, accompanied with increased bacterial loads. These findings illustrate critical roles of NLRC5/class I transactivator in MHC class I gene regulation and host defense by CD8(+) T cell responses.

Regulation of class I major histocompatibility complex (MHC) by nucleotide-binding domain, leucine-rich repeat-containing (NLR) proteins

Most of the nucleotide-binding domain, leucine-rich repeat (NLR) proteins regulate responses to microbial and damage-associated products. Class II transactivator (CIITA) has a distinct function as the master regulator of class II major histocompatibility complex (MHC-II) transcription. Recently, human NLRC5 was found to regulate MHC-I in cell lines; however, a host of conflicting positive and negative functions has been attributed to this protein. To address the function of NLRC5 in a physiologic setting, we generated an Nlrc5(-/-) strain that contains a deletion in the exon that encodes the nucleotide-binding domain. We have not detected a role for this protein in cytokine induction by pathogen-associated molecular patterns and viruses. However, Nlrc5(-/-) cells showed a dramatic decrease of classical (H-2K) and nonclassical (Tla) MHC-I expression by T/B lymphocytes, natural killer (NK) cells, and myeloid-monocytic lineages. As a comparison, CIITA did not affect mouse MHC-I expression. Nlrc5(-/-) splenocytes and bone marrow-derived macrophages were able to up-regulate MHC-I in response to IFN-γ; however, the absolute levels of MHC-I expression were significantly lower than WT controls. Chromatin immunoprecipitation of IFN-γ-treated cells indicates that Nlrc5 reduced the silencing H3K27me3 histone modification, but did not affect the activating AcH3 modification on a MHC-I promoter. In summary, we conclude that Nlrc5 is important in the regulation of MHC-I expression by reducing H3K27me3 on MHC-I promoter and joins CIITA as an NLR subfamily that controls MHC gene transcription.

NLRC5 controls basal MHC class I gene expression in an MHC enhanceosome-dependent manner

Nucleotide-binding domain and leucine-rich repeat (NLR) proteins play important roles in innate immune responses as pattern-recognition receptors. Although most NLR proteins act in cell autonomous immune pathways, some do not function as classical pattern-recognition receptors. One such NLR protein is the MHC class II transactivator, the master regulator of MHC class II gene transcription. In this article, we report that human NLRC5, which we recently showed to be involved in viral-mediated type I IFN responses, shuttles to the nucleus and activates MHC class I gene expression. Knockdown of NLRC5 in different human cell lines and primary dermal fibroblasts leads to reduced MHC class I expression, whereas introduction of NLRC5 into cell types with very low expression of MHC class I augments MHC class I expression to levels comparable to those found in lymphocytes. Expression of NLRC5 positively correlates with MHC class I expression in human tissues. Functionally, we show that both the N-terminal effector domain of NLRC5 and its C-terminal leucine-rich repeat domain are needed for activation of MHC class I expression. Moreover, nuclear shuttling and function depend on a functional Walker A motif. Finally, we identified a promoter sequence in the MHC class I promoter, the X1 box, to be involved in NLRC5-mediated MHC class I gene activation. Taken together, this suggested that NLRC5 acts in a manner similar to class II transactivator to drive MHC expression and revealed NLRC5 as an important regulator of basal MHC class I expression.