Tumor immunity is enhanced in mice expressing the pro-autoimmune allele of tyrosine phosphatase Ptpn22, but not in Ptpn22 knock-out mice

The 1858C>T allele of the tyrosine phosphatase PTPN22 (causing amino acid substitution R620W in encoded protein Lyp) is present in 5–10% of the North American population and is strongly associated with numerous autoimmune diseases. Although much research has been done to define how this allele potentiates autoimmunity, the influence PTPN22 and its pro-autoimmune allele has in tumor immunity is poorly defined. To interrogate the role this allele has during the anti-tumor immune response, we used CRISPR/Cas9 to generate mice in which the ortholog of Lyp, PEP, is mutated at position 619 to produce the relevant pro-autoimmune mutation (PEP-619WW) or lack Ptpn22 expression (PEP-null). Using the B16 and other tumor models, we tested the hypothesis that pleiotropic effects of the PTPN22 pro-autoimmune allele enhances tumor immunity. Results of this study show that PEP-619WW mice, but not PEP-null mice, resist tumor growth as compared with wildtype mice. Consistent with these results, tumors from PEP-619WW mice have more CD45 infiltrates containing; more activated CD8 T cell and CD4 T cells, more cDC1 cells, and less MDSCs than WT animals. Interestingly, the tumor infiltrating PEP-619WW cDC1s have lower PD-L1 expression compared to cDC1s from PEP-WT mice. Furthermore, using single-cell RNA sequencing we show that intra-tumoral myeloid cells from PEP-619WW mice have a more cytokine responsive transcriptional signature compared to PEP-WT cells. Our results suggest that a pro-autoimmune allele can be beneficial by promoting a strong anti-tumor immune response and may have a protective effect in this disease. Also, these data highlight an important difference between the PEP-null and PEP-619WW murine models during the tumor response.

Supported by grants from NIH (UO1 AI130842 and T32 AI007354 27).

Viral and tumor immunity is enhanced in mice expressing the pro-autoimmune allele of tyrosine phosphatase Ptpn22

The 1858C>T allele of the tyrosine phosphatase PTPN22 (causing amino acid substitution R620W) is present in 5–10% of the North American population and is strongly associated with numerous autoimmune diseases. Specifically, this alternative allele affects lymphocyte activation, toll-like receptor signaling, and cytokine production in various autoimmune contexts. Despite the importance of these inflammatory networks in pathogen and tumor clearance, the influence of PTPN22 and its pro-autoimmune allele have on viral and tumorigenic conditions is poorly defined. To interrogate these roles, we used CRISPR/Cas9 to generate mice expressing the Ptpn22 R619W molecule, which is the ortholog of R620W in humans. Using LCMV-cl13 infection and B16 tumor models, we tested the hypothesis that pleiotropic effects of Ptpn22 R619W enhances anti-viral and anti-tumor immunity. Importantly, R619W bearing mice have less tumor burden and clear chronic viral infection faster than wildtype mice. Consistent with these results, R619W mice have enhanced antigen-specific T cell activation during viral infection and more tumor infiltrating activated T cells. Also, R619W bearing mice have a more immunostimulatory cDC phenotype during disease. As this gene is expressed in all immune cells, we interrogated the role that the R619W molecule has on T cell intrinsic versus extrinsic mechanisms of T cell activation. We show an additive mechanism in which both T cell and non-T cell compartments expressing the R619W molecule cause the most T cell activation. Our results suggest that a pro-autoimmune allele can be beneficial by promoting anti-viral and anti-tumor immune responses through multiple immune cell types, and may have a protective effect in these diseases.

The Pro-autoimmune allele of tyrosine phosphatase PTPN22 enhances anti-viral and anti-tumor immunity

The 1858C>T allele of the tyrosine phosphatase PTPN22 (causing amino acid substitution R620W) is present in 5–10% of the North American population and is strongly associated with numerous autoimmune diseases. Specifically, this alternative allele affects lymphocyte activation, toll-like receptor signaling, and cytokine production in various autoimmune contexts. Despite the importance of these inflammatory networks to clear pathogens and tumors, the influence of PTPN22, and its pro-autoimmune allele, have on viral and tumorigenic conditions is still being defined. To interrogate these roles, we used CRISPR/Cas9 to generate mice expressing the Ptpn22 R619W molecule, which is the ortholog of R620W in humans. Using LCMV-cl13 infection and B16 tumor models, we tested the hypothesis that pleiotropic effects of Ptpn22 R619W enhances anti-viral and anti-tumor immunity. Importantly, R619W-bearing mice have less tumor burden and clear chronic viral infection faster than wild-type mice. Consistent with these results, R619W mice have enhanced antigen-specific T cell activation during viral infection and increased tumor-infiltrating Th1 CD4 T cells. Additionally, we define an underlying mechanism by which Ptpn22 promotes PD-L1 expression on conventional dendritic cells (cDCs) in wild-type mice, but is abrogated in R619W mice during disease. Lastly, R619W expression in lymphocytes alone can enhance T cell activation; however, the combination of R619W expressing lymphocytes and DCs enhances T cell activation even more. Our results suggest that a pro-autoimmune allele can be beneficial by promoting anti-viral and anti-tumor immune responses through multiple immune cell types, and may have a protective effect in these diseases.

Externalized histone H4 orchestrates chronic inflammation by inducing lytic cell death

The perpetuation of inflammation is an important pathophysiological contributor to the global medical burden. Chronic inflammation is promoted by non-programmed cell death1,2; however, how inflammation is instigated, its cellular and molecular mediators, and its therapeutic value are poorly defined. Here we use mouse models of atherosclerosis-a major underlying cause of mortality worldwide-to demonstrate that extracellular histone H4-mediated membrane lysis of smooth muscle cells (SMCs) triggers arterial tissue damage and inflammation. We show that activated lesional SMCs attract neutrophils, triggering the ejection of neutrophil extracellular traps that contain nuclear proteins. Among them, histone H4 binds to and lyses SMCs, leading to the destabilization of plaques; conversely, the neutralization of histone H4 prevents cell death of SMCs and stabilizes atherosclerotic lesions. Our data identify a form of cell death found at the core of chronic vascular disease that is instigated by leukocytes and can be targeted therapeutically.

The pleiotropic effects of PTPN22 and its pro-autoimmune alternative allele on the antiviral immune response and T cell exhaustion

A major alternative allele of the tyrosine phosphatase, PTPN22 1858T, is present in 5–10% of the North American population and is strongly associated with numerous autoimmune diseases. Extensive work understanding this allele in the context of autoimmune disorders has defined a role for PTPN22 in TCR and BCR signaling, toll-like receptor activation, and cytokine production. However, despite the importance of these inflammatory factors in controlling viral infection and promoting T cell exhaustion, very little work has been done to understand how PTPN22 affects these processes. Using mice deficient in expression of PTPN22, our lab previously identified a role for this gene in promoting T cell exhaustion during chronic viral infection. Yet, the mechanism by which it is acting and how the alternative allele effects T cell exhaustion remains unknown. To examine these questions, we used CRISPR/Cas9 to generate mice expressing the human-relevant PTPN22 alternative allele (PTPN22 R619W). Using the well-established LCMV-cl13 infection model in our mice, we tested the hypothesis that pleiotropic effects of PTPN22 contributes to T cell exhaustion and chronic viral infection. We address this through examining R619W expression in various immune cells contributing to viral clearance. Importantly, we determine T cells expressing R619W have increased antigen specific activation during viral infection. Additionally, we show that expression of R619W in CD8α-conventional dendritic cells reduces PD-L1 expression during viral infection and elucidate the underlying mechanism. Results of this study provide a new mechanism through which PTPN22 tempers the immune response that may be applicable to other diseases beyond chronic viral infection.

Myeloid-Specific Deletion of Peptidylarginine Deiminase 4 Mitigates Atherosclerosis

Increasing evidence suggests that neutrophil extracellular traps (NETs) may play a role in promoting atherosclerotic plaque lesions in humans and in murine models. The exact pathways involved in NET-driven atherogenesis remain to be systematically characterized. To assess the extent to which myeloid-specific peptidylarginine deiminase 4 (PAD4) and PAD4-dependent NET formation contribute to atherosclerosis, mice with myeloid-specific deletion of PAD4 were generated and backcrossed to Apoe^-/- mice. The kinetics of atherosclerosis development were determined. NETs, but not macrophage extracellular traps, were present in atherosclerotic lesions as early as 3 weeks after initiating high-fat chow. The presence of NETs was associated with the development of atherosclerosis and with inflammatory responses in the aorta. Specific deletion of PAD4 in the myeloid lineage significantly reduced atherosclerosis burden in association with diminished NET formation and reduced inflammatory responses in the aorta. NETs stimulated macrophages to synthesize inflammatory mediators, including IL-1β, CCL2, CXCL1, and CXCL2. Our data support the notion that NETs promote atherosclerosis and that the use of specific PAD4 inhibitors may have therapeutic benefits in this potentially devastating condition.

Autoimmune Risk Allele of PTPN22 influences early events post viral infection

The PTPN22 alternative allele, PTPN22 1858T, is present in 5–10% of the North American population and is considered the highest autoimmune, non-HLA, risk allele. Extensive work has been done to better understand this allele in the context of autoimmune disorders. However, the role of PTPN22 1858T in the context of viral infection remains incompletely defined. Our lab has previously defined a role for Ptpn22 in generating T cell exhaustion during chronic viral infection. Yet, the mechanism by which it is acting and how the alternative allele effects T cell exhaustion remains unknown. To directly determine this we used CRISPR/Cas9 technology to independently generate mice expressing the human-relevant Ptpn22 alternative allele. Using the well-established LCMV-cl13 infection model in our mice, we tested the hypothesis that pleiotropic effects of Ptpn22 contributes to T cell exhaustion and chronic viral infection. We address this through examination of the role of Ptpn22 in numerous immune cells contributing to viral clearance in vivo. Since early events post-infection drastically influence persistent viral infection we began our studies characterizing splenic organization, cytokines, immune cell infiltration of target organs, and viral load at 1 and 3 days post infection in our mice. Next, we further define how the Ptpn22 alternative allele effects APC functions required for proper anti-viral immune response. Lastly, we determine the state of viral clearance and T cell exhaustion at late time points post-infection in our system. Results of these studies give valuable insight into the role of Ptpn22 in multiple immune cell types that contribute to chronic viral infection and T cell exhaustion.

Targeting Aberrant Epigenetic Networks Mediated by PRMT1 and KDM4C in Acute Myeloid Leukemia

Transcriptional deregulation plays a major role in acute myeloid leukemia, and therefore identification of epigenetic modifying enzymes essential for the maintenance of oncogenic transcription programs holds the key to better understanding of the biology and designing effective therapeutic strategies for the disease. Here we provide experimental evidence for the functional involvement and therapeutic potential of targeting PRMT1, an H4R3 methyltransferase, in various MLL and non-MLL leukemias. PRMT1 is necessary but not sufficient for leukemic transformation, which requires co-recruitment of KDM4C, an H3K9 demethylase, by chimeric transcription factors to mediate epigenetic reprogramming. Pharmacological inhibition of KDM4C/PRMT1 suppresses transcription and transformation ability of MLL fusions and MOZ-TIF2, revealing a tractable aberrant epigenetic circuitry mediated by KDM4C and PRMT1 in acute leukemia.

Citrullination regulates pluripotency and histone H1 binding to chromatin

Citrullination is the post-translational conversion of an arginine residue within a protein to the non-coded amino acid citrulline. This modification leads to the loss of a positive charge and reduction in hydrogen-bonding ability. It is carried out by a small family of tissue-specific vertebrate enzymes called peptidylarginine deiminases (PADIs) and is associated with the development of diverse pathological states such as autoimmunity, cancer, neurodegenerative disorders, prion diseases and thrombosis. Nevertheless, the physiological functions of citrullination remain ill-defined, although citrullination of core histones has been linked to transcriptional regulation and the DNA damage response. PADI4 (also called PAD4 or PADV), the only PADI with a nuclear localization signal, was previously shown to act in myeloid cells where it mediates profound chromatin decondensation during the innate immune response to infection. Here we show that the expression and enzymatic activity of Padi4 are also induced under conditions of ground-state pluripotency and during reprogramming in mouse. Padi4 is part of the pluripotency transcriptional network, binding to regulatory elements of key stem-cell genes and activating their expression. Its inhibition lowers the percentage of pluripotent cells in the early mouse embryo and significantly reduces reprogramming efficiency. Using an unbiased proteomic approach we identify linker histone H1 variants, which are involved in the generation of compact chromatin, as novel PADI4 substrates. Citrullination of a single arginine residue within the DNA-binding site of H1 results in its displacement from chromatin and global chromatin decondensation. Together, these results uncover a role for citrullination in the regulation of pluripotency and provide new mechanistic insights into how citrullination regulates chromatin compaction.

Automethylation of protein arginine methyltransferase 8 (PRMT8) regulates activity by impeding S-adenosylmethionine sensitivity

Protein arginine methyltransferase (PRMT) 8 is unique among the PRMTs, as it has a highly restricted tissue expression pattern and an N terminus that contains two automethylation sites and a myristoylation site. PRMTs catalyze the transfer of a methyl group from S-adenosylmethionine (AdoMet) to a peptidylarginine on a protein substrate. Currently, the physiological roles, regulation, and cellular substrates of PRMT8 are poorly understood. However, a thorough understanding of PRMT8 kinetics should provide insights into each of these areas, thereby enhancing our understanding of this unique enzyme. In this study, we determined how automethylation regulates the enzymatic activity of PRMT8. We found that preventing automethylation with lysine mutations (preserving the positive charge of the residue) increased the turnover rate and decreased the Km of AdoMet but did not affect the Km of the protein substrate. In contrast, mimicking automethylation with phenylalanine (i.e. mimicking the increased hydrophobicity) decreased the turnover rate. The inhibitory effect of the PRMT8 N terminus could be transferred to PRMT1 by creating a chimeric protein containing the N terminus of PRMT8 fused to PRMT1. Thus, automethylation of the N terminus likely regulates PRMT8 activity by decreasing the affinity of the enzyme for AdoMet.

Identification of the low density lipoprotein (LDL) receptor-related protein-1 interactome in central nervous system myelin suggests a role in the clearance of necrotic cell debris

In the central nervous system (CNS), fast neuronal signals are facilitated by the oligodendrocyte-produced myelin sheath. Oligodendrocyte turnover or injury generates myelin debris that is usually promptly cleared by phagocytic cells. Failure to remove dying oligodendrocytes leads to accumulation of degraded myelin, which, if recognized by the immune system, may contribute to the development of autoimmunity in diseases such as multiple sclerosis. We recently identified low density lipoprotein receptor-related protein-1 (LRP1) as a novel phagocytic receptor for myelin debris. Here, we report characterization of the LRP1 interactome in CNS myelin. Fusion proteins were designed corresponding to the extracellular ligand-binding domains of LRP1. LRP1 partners were isolated by affinity purification and characterized by mass spectrometry. We report that LRP1 binds intracellular proteins via its extracellular domain and functions as a receptor for necrotic cells. Peptidyl arginine deiminase-2 and cyclic nucleotide phosphodiesterase are novel LRP1 ligands identified in our screen, which interact with full-length LRP1. Furthermore, the extracellular domain of LRP1 is a target of peptidyl arginine deiminase-2-mediated deimination in vitro. We propose that LRP1 functions as a receptor for endocytosis of intracellular components released during cellular damage and necrosis.

Activation of PAD4 in NET formation

Peptidylarginine deiminases, or PADs, convert arginine residues to the non-ribosomally encoded amino acid citrulline in a variety of protein substrates. PAD4 is expressed in granulocytes and is essential for the formation of neutrophil extracellular traps (NETs) via PAD4-mediated histone citrullination. Citrullination of histones is thought to promote NET formation by inducing chromatin decondensation and facilitating the expulsion of chromosomal DNA that is coated with antimicrobial molecules. Numerous stimuli have been reported to lead to PAD4 activation and NET formation. However, how this signaling process proceeds and how PAD4 becomes activated in cells is largely unknown. Herein, we describe the various stimuli and signaling pathways that have been implicated in PAD4 activation and NET formation, including the role of reactive oxygen species generation. To provide a foundation for the above discussion, we first describe PAD4 structure and function, and how these studies led to the development of PAD-specific inhibitors. A comprehensive survey of the receptors and signaling pathways that regulate PAD4 activation will be important for our understanding of innate immunity, and the identification of signaling intermediates in PAD4 activation may also lead to the generation of pharmaceuticals to target NET-related pathogenesis.

ATP induces protein arginine deiminase 2-dependent citrullination in mast cells through the P2X7 purinergic receptor

Posttranslational modifications regulate physiology either by directly modulating protein function or by impacting immune recognition of self-proteins. Citrullination is a posttranslational modification formed by the conversion of arginine residues into the citrulline amino acid by protein arginine deiminase (PAD) family members. We have identified mast cells as a major source of the PAD2 enzyme. Activation of the P2X7 purinergic receptor (P2X7) by the inflammatory "danger" signal ATP induces PAD2 activity and robust protein citrullination. P2X7-mediated activation of PAD2 is sensitive to p38 MAPK and protein kinase C inhibitors, and PAD2 regulates the expression of the TNFR2, Adamts-9, and Rab6b transcripts in mast cells. Further, the PAD2 enzyme and its citrullinated substrate proteins are released from mast cells on activation with ATP. PAD2 expression is closely linked with inflammation in rheumatoid arthritis (RA) synovial tissue, and PAD2 and citrullinated proteins are found in the synovial fluid of RA patients. In addition, RA is associated with the development of autoantibodies to citrullinated self-proteins. Our results suggest that P2X7 activation of mast cells may play a role in inflammation by providing PAD2 and PAD2 substrates access to the extracellular space.

Novel inhibitors for PRMT1 discovered by high-throughput screening using activity-based fluorescence polarization

Protein arginine methyltransferases (PRMTs) catalyze the posttranslational methylation of arginine using S-adenosylmethionine (SAM) as a methyl-donor. The PRMT family is widely expressed and has been implicated in biological functions such as RNA splicing, transcriptional control, signal transduction, and DNA repair. Therefore, specific inhibitors of individual PRMTs have potentially significant research and therapeutic value. In particular, PRMT1 is responsible for >85% of arginine methyltransferase activity, but currently available inhibitors of PRMT1 lack specificity, efficacy, and bioavailability. To address this limitation, we developed a high-throughput screening assay for PRMT1 that utilizes a hyper-reactive cysteine within the active site, which is lacking in almost all other PRMTs. This assay, which monitors the kinetics of the fluorescence polarization signal increase upon PRMT1 labeling by a rhodamine-containing cysteine-reactive probe, successfully identified two novel inhibitors selective for PRMT1 over other SAM-dependent methyltransferases.

PAD4 is not essential for disease in the K/BxN murine autoantibody-mediated model of arthritis

Introduction

Both murine and human genome-wide association studies have implicated peptidyl arginine deiminase (PAD4) as a susceptibility gene in rheumatoid arthritis (RA). In addition, patients with RA commonly have autoantibodies which recognize PAD4 or and/or citrullinated peptides. This study aims to evaluate the role of PAD4 in the effector phase of arthritis.

Methods

PAD4 knock out (KO) and wild type (WT) C57BL/6J mice were injected with K/BxN sera to induce disease. Progression of disease was monitored by measuring paw and ankle swelling and clinical indexes of disease, and pathogenesis was assessed by indexing of clinical progression on paws collected from WT and PAD4 KO mice injected with K/BxN serum. PAD4 activity was determined by visualization of neutrophil extracellular traps (NETs) and immunohistological analysis of histone citrullination.

Results

PAD4 activity is readily detectable in the inflamed synovium of WT but not PAD4 deficient animals, as demonstrated by histone citrullination and NET formation. However, PAD4 WT and KO animals develop K/BxN serum transfer disease with comparable severity and kinetics, with no statistically significant differences noted in clinical scores, swelling, joint erosion or joint invasion.

Conclusions

PAD4 WT and KO mice develop disease in the K/BxN serum transfer model of arthritis with similar severity and kinetics, indicating that PAD4 is dispensable in this effector phase model of disease.

PAD4-mediated neutrophil extracellular trap formation is not required for immunity against influenza infection

During an inflammatory response, neutrophils migrate to the site of infection where they can kill invading pathogens by phagocytosis, secretion of anti-microbicidal mediators or the release of neutrophil extracellular traps (NETs). NETs are specialized anti-microbial structures comprised of decondensed chromatin decorated with microbicidal agents. Increased amount of NETs have been found in patients suffering from the chronic lung inflammatory disease cystic fibrosis, correlating with increased severity of pulmonary obstruction. Furthermore, acute lung inflammation during influenza A infection is characterized by a massive influx of neutrophils into the lung. The role of NETs during virus-mediated lung inflammation is unknown. Peptidylarginine deiminase 4 (PAD4)-mediated deimination of histone H3 and H4 is required for NET formation. Therefore, we generated a PAD4-deficient mouse strain that has a striking inability to form NETs. These mice were infected with influenza A/WSN, and the disease was monitored at the level of leukocytic lung infiltration, lung pathology, viral replication, weight loss and mortality. PAD4 KO fared comparable to WT mice in all the parameters tested, but they displayed slight but statistically different weight loss kinetics during infection that was not reflected in enhanced survival. Overall, we conclude that PAD4-mediated NET formation is dispensable in a mouse model of influenza A infection.

Mast cell function is not altered by Coronin-1A deficiency

Coronin-1A is a WD repeat protein family member, highly expressed in all hematopoietic lineages, and acts as a regulator of F-actin dynamics and Ca2+ signaling. In Coro1a(Lmb3) mice results in inactivation of the protein and leads to disease resistance in a model of lupus erythematosus. In Coro1a(-/-) and Coro1a(Lmb3) mice, peripheral T cells exhibit impairments in survival, migration, activation, and Ca2+ flux. In this study, we show that in vitro-differentiated mast cells from Coro1a(Lmb3) mice are viable, developed normally, and are fully functional in assays of degranulation, cytokine secretion, and chemotactic migration, despite increased F-actin levels. In Coro1a(Lmb3) mast cells, Ca2+ flux in response to physiological FcεRI stimulation is unaffected. Finally, Coro1a(Lmb3) mice showed similar in vivo mast cell responses as the WT mice. Coronin-1B and Coronin-1C expression levels were not increased in Coro1a(Lmb3) mast cells but were higher in mast cells than in CD4 T cells or B cells in WT mice. We conclude that Coronin-1A activity is not required for mast cell function.

Effects of a novel arginine methyltransferase inhibitor on T-helper cell cytokine production

The protein arginine methyltransferase (PRMT) family of enzymes catalyzes the transfer of methyl groups from S-adenosylmethionine to the guanidino nitrogen atom of peptidylarginine to form monomethylarginine or dimethylarginine. We created several less polar analogs of the specific PRMT inhibitor arginine methylation inhibitor-1, and one such compound was found to have improved PRMT inhibitory activity over the parent molecule. The newly identified PRMT inhibitor modulated T-helper-cell function and thus may serve as a lead for further inhibitors useful for the treatment of immune-mediated disease.

Negative Regulation of NIP45 Function by Peptidylarginine Deminase 4 (87.28)

IL-4 production in Th2 lymphocytes is regulated by the nuclear factor of activated T-cells (NFAT) and NFAT-interacting protein 45kDa (NIP45). Recently, we showed that arginine methylation of NIP45 modulates its interaction with NFAT and augments IL-4 transcription. Here we report that NIP45 methylation is negatively regulated by peptidylarginine-deiminase 4 (PAD4) via deimination of arginine residues and generation of the atypical amino acid citrulline. NIP45 loses its ability to become methylated after deimination by PAD4. Ectopic expression of PAD4 impairs the association of NIP45 with NFAT and profoundly inhibits IL-4 promoter activity. Whereas, knockdown of PAD4 expression in Th2 cells by a PAD4-directed shRNA-expressing retrovirus leads to elevated IL-4 production. Interestingly, a PAD4 variant is association with rheumatoid arthritis (RA) in a Japanese population. Indeed, many autoantibodies in RA are directed against citrullinated proteins. It has been proposed that PAD4 is linked to RA because citrullination of peptides leads to a breakdown of self-tolerance to self-antigens. Our data suggest that PAD4 may also influence RA development through regulation of the cytokine milieu. Modification of NIP45 by PAD4 provides a novel negative regulatory mechanism whereby NFAT and NIP45 control IL-4 and potentially other cytokines production.

Signaling pathways in Th2 development

In order for an immune response to be successful, it must be of the appropriate type and magnitude. Intracellular residing pathogens require a cell-mediated immune response, whereas extracellular pathogens evoke a humoral immune response. T-helper (Th) cells orchestrate the immune response and are divided into two subsets, Th1 and Th2 cells. Here, we discuss the mechanisms of Th2 development with a focus on signal transduction pathways that influence Th2 differentiation.

Arginine Methylation of NIP45 Modulates Cytokine Gene Expression in Effector T Lymphocytes

Posttranslational modification of proteins within T cell receptor signaling cascades allows T lymphocytes to rapidly initiate an appropriate immune response. Here we report a role for arginine methylation in regulating cytokine gene transcription in the T helper lymphocyte. Inhibition of arginine methylation impaired the expression of several cytokine genes, including the signature type 1 and type 2 helper cytokines, interferon gamma, and interleukin-4. T cell receptor signaling increased expression of the protein arginine methyltransferase PRMT1, which in turn methylated the nuclear factor of activated T cells (NFAT) cofactor protein, NIP45. Arginine methylation of the amino terminus of NIP45 modulated its interaction with NFAT and resulted in augmented cytokine production, while T cells from mice lacking NIP45 had impaired expression of IFNgamma and IL-4. Covalent modification of NIP45 by arginine methylation is an important mechanism of regulating the expression of NFAT-dependent cytokine genes.

Interferon regulatory factor 4 (IRF4) interacts with NFATc2 to modulate interleukin 4 gene expression

Proteins of the nuclear factor of activated T cells (NFAT) family of transcription factors are critical for lymphocyte activation in the immune system. In particular, NFATs are important regulators of inducible IL-4 gene expression. Interferon regulatory factor 4 (IRF4) is an immune system-restricted interferon regulatory factor that is required for lymphocyte activation, but its molecular functions in the T lineage remain to be elucidated. We demonstrate that IRF4 potently synergizes with NFATc2 to specifically enhance NFATc2-driven transcriptional activation of the IL-4 promoter. This function is dependent on the physical interaction of IRF4 with NFATc2. IRF4 synergizes with NFATc2 and the IL-4-inducing transcription factor, c-maf, to augment IL-4 promoter activity as well as to elicit significant levels of endogenous IL-4 production. Furthermore, naïve T helper cells from mice lacking IRF4 are compromised severely for the production of IL-4 and other Th2 cytokines. The identification of IRF4 as a partner for NFATc2 in IL-4 gene regulation provides an important molecular function for IRF4 in T helper cell differentiation.

Analysis of protein arginine methylation and protein arginine-methyltransferase activity

Posttranslational modification of proteins allows cells to adapt and react quickly to their environment beyond the boundaries set forth by genetic code. Arginine methylation, a protein modification discovered almost 30 years ago, has recently experienced a renewed interest as several new arginine methyltransferases have been identified and numerous proteins were found to be regulated by methylation on arginine residues. Until recently, the detection of arginine methylation required the use of chromatography and mass-spectrometrical analysis. The following protocol provides guidelines for the straightforward identification of arginine-methylated proteins, made possible by the availability of novel, commercially available reagents.

Tumor necrosis factor receptor-associated factor (TRAF)2 represses the T helper cell type 2 response through interaction with NFAT-interacting protein (NIP45)

Recently we have identified a novel protein NIP45 (nuclear factor of activated T cells [NFAT]-interacting protein) which substantially augments interleukin (IL)-4 gene transcription. The provision of NIP45 together with NFAT and the T helper cell type 2 (Th2)-specific transcription factor c-Maf to cells normally refractory to IL-4 production, such as B cells or Th1 clones, results in substantial IL-4 secretion to levels that approximate those produced by primary Th2 cells. In studies designed to further our understanding of NIP45 activity, we have uncovered a novel facet of IL-4 gene regulation. We present evidence that members of the tumor necrosis factor receptor-associated factor (TRAF) family of proteins, generally known to function as adapter proteins that transduce signals from the tumor necrosis factor receptor superfamily, contribute to the repression of IL-4 gene transcription and that this effect is mediated through their interaction with NIP45.

Arginine methylation of STAT1 modulates IFNalpha/beta-induced transcription

Transcriptional induction by interferons requires the tyrosine and serine phosphorylation of STAT transcription factors. The N-terminal region is highly homologous among the STAT proteins and surrounds a completely conserved arginine residue. Here we demonstrate arginine methylation of STAT1 by the protein arginine methyl-transferase PRMT1 as a novel requirement for IFNalpha/beta-induced transcription. Methyl-thioadenosine, a methyl-transferase inhibitor that accumulates in many transformed cells, inhibits STAT1-mediated IFN responses. This inhibition arises from impaired STAT1-DNA binding due to an increased association of the STAT inhibitor PIAS1 with phosphorylated STAT1 dimers in the absence of arginine methylation. Thus, arginine methylation of STAT1 is an additional posttranslational modification regulating transcription factor function, and alteration of arginine methylation might be responsible for the lack of interferon responsiveness observed in many malignancies.

Characterization of a nuclear deformed epidermal autoregulatory factor-1 (DEAF-1)-related (NUDR) transcriptional regulator protein

A monkey kidney cDNA that encodes a nuclear regulatory factor was identified by expression and affinity binding to a synthetic retinoic acid response element (RARE) and was used to isolate human placental and rat germ cell cDNAs by hybridization. The cDNAs encode a 59-kDa protein [nuclear DEAF-1-related (NUDR)] which shows sequence similarity to the Drosophila Deformed epidermal autoregulatory factor-1 (DEAF-1), a nonhomeodomain cofactor of embryonic Deformed gene expression. Similarities to other proteins indicate five functional domains in NUDR including an alanine-rich region prevalent in developmental transcription factors, a domain found in the promyelocytic leukemia-associated SP100 proteins, and a zinc finger homology domain associated with the AML1/MTG8 oncoprotein. Although NUDR mRNA displayed a wide tissue distribution in rats, elevated levels of protein were only observed in testicular germ cells, developing fetus, and transformed cell lines. Nuclear localization of NUDR was demonstrated by immunocytochemistry and by a green fluorescent protein-NUDR fusion protein. Site-directed mutagenesis of a nuclear localization signal resulted in cytoplasmic localization of the protein and eliminated NUDR-dependent transcriptional activation. Recombinant NUDR protein showed affinity for the RARE in mobility shifts; however it was efficiently displaced by retinoic acid receptor (RAR)/retinoid X receptor (RXR) complexes. In transient transfections, NUDR produced up to 26-fold inductions of a human proenkephalin promoter-reporter plasmid, with minimal effects on the promoters for prodynorphin or thymidine kinase. Placement of a RARE on the proenkephalin promoter increased NUDR-dependent activation to 41-fold, but this RARE-dependent increase was not transferable to a thymidine kinase promoter. Recombinant NUDR protein showed minimal binding affinity for proenkephalin promoter sequences, but was able to select DNA sequences from a random oligonucleotide library that had similar core-binding motifs (TTCG) as those recognized by DEAF-1. This motif is also present between the half-sites of several endogenous RAREs. The derived consensus- binding motif recognized by NUDR (TTCGGGNNTTTCCGG) was confirmed by mobility shift and deoxyribonuclease I (DNase I) protection assays; however, the consensus sequence was also unable to confer NUDR-dependent transcriptional activation to the thymidine kinase promoter. Our data suggests that NUDR may activate transcription independently of promoter binding, perhaps through protein-protein interaction with basal transcription factors, or by activation of secondary factors. The sequence and functional similarities between NUDR and DEAF-1 suggest that NUDR may also act as a cofactor to regulate the transcription of genes during fetal development or differentiation of testicular cells.