T Cell Repertoire Homogeneity and Blood-Gut Overlap in Patients With Inflammatory Bowel Disease.

BACKGROUND & AIMS: Inflammatory bowel disease (IBD) causes a marked increase in the number of T cells in the intestinal mucosa. Debate exists about whether these excess cells arise from local clonal proliferation or recruitment from the periphery. METHODS: CD8+ T cells were sorted from colon biopsy specimens and blood for T-cell receptor (TCR) ß-chain sequencing. Biopsy specimens from inflamed or uninflamed colon from ulcerative colitis or Crohn's disease cohorts were compared with colon biopsy specimens from people without IBD, as well as with autologous blood α4ß7+, α4ß7- effector/memory, terminal effector/memory CD45RA+ T cell, and mucosal-associated invariant T-cell CD8 subpopulations. RESULTS: CD8 TCR diversity in mucosa and blood did not correlate with inflammation. Repertoire overlap between any 2 distinct locations of a given person's colon was consistently high, although often lower between inflamed and uninflamed sites. CD8 TCR repertoires overlapped between the colon and each peripheral blood subpopulation studied, with the highest overlap seen for integrin α4ß7+ T cells. Inflamed tissue consistently overlapped more than uninflamed tissue with each blood subpopulation. CONCLUSIONS: CD8 T-cell clones are spread homogenously throughout the length of the colon. Although TCR repertoire overlap is greater within than between inflamed and uninflamed colon segments, a similar TCR diversity in both argues against local clonal expansion being the main source of excess cytotoxic T cells in inflamed mucosa. Rather, the increased TCR overlap observed between blood and inflamed mucosa supports the significance of T-cell trafficking in IBD pathogenesis, particularly concerning α4ß7+ T-cell populations.

Janus kinase inhibitors differentially inhibit specific cytokine signals in the mesenteric lymph node cells of IBD patients.

BACKGROUND: Janus kinase (JAK) inhibitors (JAKinibs) are effective small molecule therapies for treating Crohn's Disease (CD) and Ulcerative Colitis (UC), collectively known as inflammatory bowel disease (IBD). By preventing JAKs from phosphorylating signal transducer and activator of transcription proteins, JAKinibs disrupt cytokine signaling pathways that promote inflammation. Despite considerable overlap in the JAKs they target, first and second generation JAKinibs display different clinical efficacies in CD and UC. METHODS: We conducted a comparative phosflow study of four JAKinibs (filgotinib, upadacitinib, tofacitinib, and deucravacitinib) to observe subtle mechanistic differences that may dictate their clinical behavior. Resected mesenteric lymph node (MLN) cells from 19 patients (9 CD, 10 UC) were analyzed by flow cytometry in the presence or absence of different cytokine stimuli and titrated JAKinibs. RESULTS: We found a higher potency of the JAK 1/3-preferential inhibitor, tofacitinib, for JAK 3-dependent cytokine signaling pathways in comparison to filgotinib, but a higher potency of the JAK 1-preferential inhibitors, filgotinib and upadacitinib, for JAK 3-independent cytokine signaling pathways. Deucravacitinib, a TYK2-preferential inhibitor, demonstrated a much narrower selectivity by inhibiting only IL-10 and IFN-ßpathways, albeit more potently than the other JAKinibs . Additionally, we found some differences in the sensitivity of immune cells from CD versus UC and patients with versus without a CD-associated NOD2 polymorphism to phosphorylate signal transducer and activator of transcriptions in response to specific cytokine stimulation. CONCLUSIONS: Despite their similarities, differences exist in the relative potencies of different JAKinibs against distinct cytokine families to explain their clinical efficacy.

Characterization of the mechanism of action of lanraplenib, a novel spleen tyrosine kinase inhibitor, in models of lupus nephritis.

BACKGROUND: B cells are critical mediators of systemic lupus erythematosus (SLE) and lupus nephritis (LN), and antinuclear antibodies can be found in the serum of approximately 98% of patients with SLE. Spleen tyrosine kinase (SYK) is a nonreceptor tyrosine kinase that mediates signaling from immunoreceptors, including the B cell receptor. Active, phosphorylated SYK has been observed in tissues from patients with SLE or cutaneous lupus erythematosus, and its inhibition is hypothesized to ameliorate disease pathogenesis. We sought to evaluate the efficacy and characterize the mechanism of action of lanraplenib, a selective oral SYK inhibitor, in the New Zealand black/white (NZB/W) murine model of SLE and LN. METHODS: Lanraplenib was evaluated for inhibition of primary human B cell functions in vitro. Furthermore, the effect of SYK inhibition on ameliorating LN-like disease in vivo was determined by treating NZB/W mice with lanraplenib, cyclophosphamide, or a vehicle control. Glomerulopathy and immunoglobulin G (IgG) deposition were quantified in kidneys. The concentration of proinflammatory cytokines was measured in serum. Splenocytes were analyzed by flow cytometry for B cell maturation and T cell memory maturation, and the presence of T follicular helper and dendritic cells. RESULTS: In human B cells in vitro, lanraplenib inhibited B cell activating factor-mediated survival as well as activation, maturation, and immunoglobulin M production. Treatment of NZB/W mice with lanraplenib improved overall survival, prevented the development of proteinuria, and reduced blood urea nitrogen concentrations. Kidney morphology was significantly preserved by treatment with lanraplenib as measured by glomerular diameter, protein cast severity, interstitial inflammation, vasculitis, and frequency of glomerular crescents; treatment with lanraplenib reduced glomerular IgG deposition. Mice treated with lanraplenib had reduced concentrations of serum proinflammatory cytokines. Lanraplenib blocked disease-driven B cell maturation and T cell memory maturation in the spleen. CONCLUSIONS: Lanraplenib blocked the progression of LN-like disease in NZB/W mice. Human in vitro and murine in vivo data suggest that lanraplenib may be efficacious in preventing disease progression in patients with LN at least in part by inhibiting B cell maturation. These data provide additional rationale for the use of lanraplenib in the treatment of SLE and LN.

The BET inhibitor GS-5829 targets chronic lymphocytic leukemia cells and their supportive microenvironment.

Despite major improvements in treatment outcome with novel targeted therapies, such as the Bruton tyrosine kinase (BTK) inhibitor ibrutinib, chronic lymphocytic leukemia (CLL) remains incurable in the majority of patients. Activation of PI3K, NF-κB, and/or MYC has been linked to residual disease and/or resistance in ibrutinib-treated patients. These pathways can be targeted by inhibitors of bromodomain and extra-terminal (BET) proteins. Here we report about the preclinical activity of GS-5829, a novel BET inhibitor, in CLL. GS-5829 inhibited CLL cell proliferation and induced leukemia cell apoptosis through deregulation of key signaling pathways, such as BLK, AKT, ERK1/2, and MYC. IκBα modulation indicates that GS-5829 also inhibited NF-κB signaling. GS-5829-induced apoptosis resulted from an imbalance between positive (BIM) and negative regulators (BCL-XL) of the intrinsic apoptosis pathway. The antileukemia activity of GS-5829 increased synergistically in combinations with B-cell receptor signaling inhibitors, the BTK inhibitor ibrutinib, the PI3Kδ inhibitor idelalisib, and the SYK inhibitor entospletinib. In cocultures that mimic the lymph node microenvironment, GS-5829 inhibited signaling pathways within nurselike cells and their growth, indicating that BET inhibitors also can target the supportive CLL microenvironment. Collectively, these data provide a rationale for the clinical evaluation of BET inhibitors in CLL.

Effects of GS-9876, a novel spleen tyrosine kinase inhibitor, on platelet function and systemic hemostasis.

INTRODUCTION: Spleen tyrosine kinase (SYK) mediates signal transduction in multiple hematopoietic cells, including platelets. SYK signals downstream of immunoreceptors and SYK inhibition may ameliorate disease pathology in multiple autoimmune disorders; however, the impact of SYK inhibition in platelets and its potential relevance to bleeding is not fully understood. These studies evaluated the effect of an oral SYK inhibitor, GS-9876, on platelets in vitro and in vivo, and the impact of GS-9876 plus non-steroidal anti-inflammatory drugs (NSAIDs) on platelet aggregation. MATERIAL AND METHODS: The effect of GS-9876 on platelet activation, aggregation, and binding was characterized by western blotting, aggregometry, fluorescence-activated cell sorting, and microscopy techniques. The effect of GS-9876 on in vivo bleeding time (BT) was determined in cynomolgus monkeys and humans. RESULTS: GS-9876 inhibited glycoprotein VI (GPVI)-induced phosphorylation of linker for activation of T cells and phospholipase Cγ2, platelet activation and aggregation in human whole blood, and platelet binding to collagen under arterial flow. Ex vivo, GPVI-stimulated platelet aggregation was inhibited in GS-9876-treated monkeys without a concomitant increase in BT. Similarly, orally administered GS-9876 did not increase BT in humans. No in vitro additive effects on inhibition of platelet aggregation were observed with GS-9876 plus NSAIDs in human blood. CONCLUSIONS: GS-9876 inhibited SYK activity in platelets via the GPVI receptor without prolonging BT in monkeys or humans. Furthermore, GS-9876 did not increase inhibition of platelet aggregation by NSAIDs in vitro, suggesting that these agents can potentially be combined without increasing bleeding risk in humans.

Regulation of centromere localization of the Drosophila Shugoshin MEI-S332 and sister-chromatid cohesion in meiosis.

The Shugoshin (Sgo) protein family helps to ensure proper chromosome segregation by protecting cohesion at the centromere by preventing cleavage of the cohesin complex. Some Sgo proteins also influence other aspects of kinetochore-microtubule attachments. Although many Sgo members require Aurora B kinase to localize to the centromere, factors controlling delocalization are poorly understood and diverse. Moreover, it is not clear how Sgo function is inactivated and whether this is distinct from delocalization. We investigated these questions in Drosophila melanogaster, an organism with superb chromosome cytology to monitor Sgo localization and quantitative assays to test its function in sister-chromatid segregation in meiosis. Previous research showed that in mitosis in cell culture, phosphorylation of the Drosophila Sgo, MEI-S332, by Aurora B promotes centromere localization, whereas Polo phosphorylation promotes delocalization. These studies also suggested that MEI-S332 can be inactivated independently of delocalization, a conclusion supported here by localization and function studies in meiosis. Phosphoresistant and phosphomimetic mutants for the Aurora B and Polo phosphorylation sites were examined for effects on MEI-S332 localization and chromosome segregation in meiosis. Strikingly, MEI-S332 with a phosphomimetic mutation in the Aurora B phosphorylation site prematurely dissociates from the centromeres in meiosis I. Despite the absence of MEI-S332 on meiosis II centromeres in male meiosis, sister chromatids segregate normally, demonstrating that detectable levels of this Sgo are not essential for chromosome congression, kinetochore biorientation, or spindle assembly.

A potential therapeutic strategy for chronic lymphocytic leukemia by combining Idelalisib and GS-9973, a novel spleen tyrosine kinase (Syk) inhibitor.

Agents that target B-cell receptor (BCR) signaling in lymphoid malignancies including idelalisib (GS-1101) and fostamatinib which inhibit the delta isoform of PI3 kinase (PI3Kd) and spleen tyrosine kinase (Syk) respectively have shown significant clinical activity. By disrupting B-cell signaling pathways, idelalisib treatment has been associated with a dramatic lymph node response, but eradication of disease and relapse in high risk disease remain challenges. Targeting the BCR signaling pathway with simultaneous inhibition of PI3Kd and Syk has not yet been reported. We evaluated the pre-clinical activity of idelalisib combined with the novel and selective Syk inhibitor GS-9973 in primary peripheral blood and bone marrow Chronic Lymphocytic Leukemia (CLL) samples. Both PI3Kd and Syk inhibition reduced CLL survival and in combination induced synergistic growth inhibition and further disrupted chemokine signaling at nanomolar concentrations including in bone marrow derived and poor risk samples. Simultaneous targeting of these kinases may significantly increase clinical activity.

Suppression analysis of esa1 mutants in Saccharomyces cerevisiae links NAB3 to transcriptional silencing and nucleolar functions.

The acetyltransferase Esa1 is essential in the yeast Saccharomyces cerevisiae and plays a critical role in multiple cellular processes. The most well-defined targets for Esa1 are lysine residues on histones. However, an increasing number of nonhistone proteins have recently been identified as substrates of Esa1. In this study, four genes (LYS20, LEU2, VAP1, and NAB3) were identified in a genetic screen as high-copy suppressors of the conditional temperature-sensitive lethality of an esa1 mutant. When expressed from a high-copy plasmid, each of these suppressors rescued the temperature-sensitivity of an esa1 mutant. Only NAB3 overexpression also rescued the rDNA-silencing defects of an esa1 mutant. Strengthening the connections between NAB3 and ESA1, mutants of nab3 displayed several phenotypes similar to those of esa1 mutants, including increased sensitivity to the topoisomerase I inhibitor camptothecin and defects in rDNA silencing and cell-cycle progression. In addition, nuclear localization of Nab3 was altered in the esa1 mutant. Finally, posttranslational acetylation of Nab3 was detected in vivo and found to be influenced by ESA1.

The selectivity of austocystin D arises from cell-line-specific drug activation by cytochrome P450 enzymes.

The natural product austocystin D was identified as a potent cytotoxic agent with in vivo antitumor activity and selectivity for cells expressing the multidrug resistance transporter MDR1. We sought to elucidate the mechanism of austocystin D's selective cytotoxic activity. Here we show that the selective cytotoxic action of austocystin D arises from its selective activation by cytochrome P450 (CYP) enzymes in specific cancer cell lines, leading to induction of DNA damage in cells and in vitro. The potency and selectivity of austocystin D is lost upon inhibition of CYP activation and does not require MDR1 expression or activity. Furthermore, the pattern of cytotoxicity of austocystin D was distinct from doxorubicin and etoposide and unlike aflatoxin B(1), a compound that resembles austocystin D and is also activated by CYP enzymes to induce DNA damage. Theses results suggest that austocystin D may be of clinical benefit for targeting or overcoming chemoresistance.

Sister chromatid cohesion at the centromere: confrontation between kinases and phosphatases?

Accurate chromosome segregation in mitosis and meiosis requires that the cohesin complex be protected at the centromere by the Shugoshin/MEI-S332 protein family. Recent studies show that Sgo directly binds the phosphatase PP2A, tethering it to the centromere where it can protect cohesin subunits from phosphorylation, and that localization of Sgo/MEI-S332 itself is regulated by phosphorylation.

Distinct roles for the essential MYST family HAT Esa1p in transcriptional silencing.

Among acetyltransferases, the MYST family enzyme Esa1p is distinguished for its essential function and contribution to transcriptional activation and DNA double-stranded break repair. Here we report that Esa1p also plays a key role in silencing RNA polymerase II (Pol II)-transcribed genes at telomeres and within the ribosomal DNA (rDNA) of the nucleolus. These effects are mediated through Esa1p's HAT activity and correlate with changes within the nucleolus. Esa1p is enriched within the rDNA, as is the NAD-dependent protein deacetylase Sir2p, and the acetylation levels of key Esa1p histone targets are reduced in the rDNA in esa1 mutants. Although mutants of both ESA1 and SIR2 have enhanced rates of rDNA recombination, esa1 effects are more modest yet result in distinct structural changes of rDNA chromatin. Surprisingly, increased expression of ESA1 can bypass the requirement for Sir2p in rDNA silencing, suggesting that these two enzymes with seemingly opposing activities both contribute to achieve optimal nucleolar chromatin structure and function.

POLO kinase regulates the Drosophila centromere cohesion protein MEI-S332.

Accurate segregation of chromosomes is critical to ensure that each daughter cell receives the full genetic complement. Maintenance of cohesion between sister chromatids, especially at centromeres, is required to segregate chromosomes precisely during mitosis and meiosis. The Drosophila protein MEI-S332, the founding member of a conserved protein family, is essential in meiosis for maintaining cohesion at centromeres until sister chromatids separate at the metaphase II/anaphase II transition. MEI-S332 localizes onto centromeres in prometaphase of mitosis or meiosis I, remaining until sister chromatids segregate. We elucidated a mechanism for controlling release of MEI-S332 from centromeres via phosphorylation by POLO kinase. We demonstrate that POLO antagonizes MEI-S332 cohesive function and that full POLO activity is needed to remove MEI-S332 from centromeres, yet this delocalization is not required for sister chromatid separation. POLO phosphorylates MEI-S332 in vitro, POLO and MEI-S332 bind each other, and mutation of POLO binding sites prevents MEI-S332 dissociation from centromeres.