The therapeutic mavericks: Potent immunomodulating chaperones capable of treating human diseases.

Two major chaperones, calreticulin (CRT) and binding immunoglobulin protein (GRP78/BiP) dependent on their location, have immunoregulatory or anti-inflammatory functions respectively. CRT induces pro-inflammatory cytokines, dendritic cell (DC) maturation and activates cytotoxic T cells against tumours. By contrast, GRP78/BiP induces anti-inflammatory cytokines, inhibits DC maturation and heightens T-regulatory cell responses. These latter functions rebalance immune homeostasis in inflammatory diseases, such as rheumatoid arthritis. Both chaperones are therapeutically relevant agents acting primarily on monocytes/DCs. Endogenous exposure of CRT on cancer cell surfaces acts as an 'eat-me' signal and facilitates improved elimination of stressed and dying tumour cells by DCs. Therefore, therapeutics that promote endogenous CRT translocation to the cell surface can improve the removal of cancer cells. However, infused recombinant CRT dampens this cancer cell eradication by binding directly to the DCs. Low levels of endogenous BiP appear as a surface biomarker of endoplasmic reticulum (ER) stress in some types of tumour cells, a reflection of cells undergoing proliferation, in which resulting hypoxia and nutrient deprivation perturb ER homeostasis triggering the unfolded protein response, leading to increased expression of GRP78/BiP and altered cellular location. Conversely, infusion of an analogue of GRP78/BiP (IRL201805) can lead to long-term immune resetting and restoration of immune homeostasis. The therapeutic potential of both chaperones relies on them being relocated from their intracellular ER environment. Ongoing clinical trials are employing therapeutic interventions to either enhance endogenous cell surface CRT or infuse IRL201805, thereby triggering several disease-relevant immune responses leading to a beneficial clinical outcome.

Upadacitinib as induction and maintenance therapy for moderately to severely active ulcerative colitis: results from three phase 3, multicentre, double-blind, randomised trials.

BACKGROUND: There is a great unmet need for advanced therapies that provide rapid, robust, and sustained disease control for patients with ulcerative colitis. We assessed the efficacy and safety of upadacitinib, an oral selective Janus kinase 1 inhibitor, as induction and maintenance therapy in patients with moderately to severely active ulcerative colitis. METHODS: This phase 3, multicentre, randomised, double-blind, placebo-controlled clinical programme consisted of two replicate induction studies (U-ACHIEVE induction [UC1] and U-ACCOMPLISH [UC2]) and a single maintenance study (U-ACHIEVE maintenance [UC3]). The studies were conducted across Europe, North and South America, Australasia, Africa, and the Asia-Pacific region at 199 clinical centres in 39 countries (UC1), 204 clinical centres in 40 countries (UC2), and 195 clinical centres in 35 countries (UC3). Patients aged 16-75 years with moderately to severely active ulcerative colitis (Adapted Mayo score 5-9; endoscopic subscore 2 or 3) for at least 90 days were randomly assigned (2:1) to oral upadacitinib 45 mg once daily or placebo for 8 weeks (induction studies). Patients who achieved clinical response following 8-week upadacitinib induction were re-randomly assigned (1:1:1) to upadacitinib 15 mg, upadacitinib 30 mg, or placebo for 52 weeks (maintenance study). All patients were randomly assigned using web-based interactive response technology. The primary endpoints were clinical remission per Adapted Mayo score at week 8 (induction) and week 52 (maintenance). The efficacy analyses in the two induction studies were based on the intent-to-treat population, which included all randomised patients who received at least one dose of treatment. In the maintenance study, the primary efficacy analyses reported in this manuscript were based on the first 450 (planned) clinical responders to 8-week induction therapy with upadacitinib 45 mg once daily. The safety analysis population in the induction studies consisted of all randomised patients who received at least one dose of treatment; in the maintenance study, this population included all patients who received at least one dose of treatment as part of the primary analysis population. These studies are registered at ClinicalTrials.gov, NCT02819635 (U-ACHIEVE) and NCT03653026 (U-ACCOMPLISH). FINDINGS: Between Oct 23, 2018, and Sept 7, 2020, 474 patients were randomly assigned to upadacitinib 45 mg once daily (n=319) or placebo (n=155) in UC1. Between Dec 6, 2018, and Jan 14, 2021, 522 patients were randomly assigned to upadacitinib 45 mg once daily (n=345) or placebo (n=177) in UC2. In UC3, a total of 451 patients (21 from the phase 2b study, 278 from UC1, and 152 from UC2) who achieved a clinical response after 8 weeks of upadacitinib induction treatment were randomly assigned again to upadacitinib 15 mg (n=148), upadacitinib 30 mg (n=154), and placebo (n=149) in the primary analysis population. Statistically significantly more patients achieved clinical remission with upadacitinib 45 mg (83 [26%] of 319 patients in UC1 and 114 [34%] of 341 patients in UC2) than in the placebo group (seven [5%] of 154 patients in UC1 and seven [4%] of 174 patients; p<0·0001; adjusted treatment difference 21·6% [95% CI 15·8-27·4] for UC1 and 29·0% [23·2-34·7] for UC2). In the maintenance study, clinical remission was achieved by statistically significantly more patients receiving upadacitinib (15 mg 63 [42%] of 148; 30 mg 80 [52%] of 154) than those receiving placebo (18 [12%] of 149; p<0·0001; adjusted treatment difference 30·7% [21·7-39·8] for upadacitinib 15 mg vs placebo and 39·0% [29·7-48·2] for upadacitinib 30 mg vs placebo). The most commonly reported adverse events in UC1 were nasopharyngitis (15 [5%] of 319 in the upadacitinib 45 mg group vs six [4%] of 155 in the placebo group), creatine phosphokinase elevation (15 [4%] vs three [2%]), and acne (15 [5%] vs one [1%]). In UC2, the most frequently reported adverse event was acne (24 [7%] of 344 in the upadacitinib 45 mg group vs three [2%] of 177 in the placebo group). In both induction studies, serious adverse events and adverse events leading to discontinuation of treatment were less frequent in the upadacitinib 45 mg group than in the placebo group (serious adverse events eight [3%] vs nine (6%) in UC1 and 11 [3%] vs eight [5%] in UC2; adverse events leading to discontinuation six [2%] vs 14 [9%] in UC1 and six [2%] vs nine [5%] in UC2). In UC3, the most frequently reported adverse events (≥5%) were worsening of ulcerative colitis (19 [13%] of 148 in the upadacitinib 15 mg group vs 11 [7%] of 154 in the upadacitinib 30 mg group vs 45 [30%] of 149 in the placebo group), nasopharyngitis (18 [12%] vs 22 [14%] vs 15 [10%]), creatine phosphokinase elevation (nine [6%] vs 13 [8%] vs three [2%]), arthralgia (nine [6%] vs five [3%] vs 15 [10%]), and upper respiratory tract infection (seven [5%] vs nine [6%] vs six [4%]). The proportion of serious adverse events (ten [7%] vs nine [6%] vs 19 [13%]) and adverse events leading to discontinuation (six [4%] vs ten [6%] vs 17 [11%]) was lower in both upadacitinib groups than in the placebo group. Events of cancer, adjudicated major adverse cardiac events, or venous thromboembolism were reported infrequently. There were no treatment-related deaths. INTERPRETATION: Upadacitinib demonstrated a positive efficacy and safety profile and could be an effective treatment option for patients with moderately to severely active ulcerative colitis. FUNDING: AbbVie.

Sir2 mitigates an intrinsic imbalance in origin licensing efficiency between early- and late-replicating euchromatin.

A eukaryotic chromosome relies on the function of multiple spatially distributed DNA replication origins for its stable inheritance. The spatial location of an origin is determined by the chromosomal position of an MCM complex, the inactive form of the DNA replicative helicase that is assembled onto DNA in G1-phase (also known as origin licensing). While the biochemistry of origin licensing is understood, the mechanisms that promote an adequate spatial distribution of MCM complexes across chromosomes are not. We have elucidated a role for the Sir2 histone deacetylase in establishing the normal distribution of MCM complexes across Saccharomyces cerevisiae chromosomes. In the absence of Sir2, MCM complexes accumulated within both early-replicating euchromatin and telomeric heterochromatin, and replication activity within these regions was enhanced. Concomitantly, the duplication of several regions of late-replicating euchromatin were delayed. Thus, Sir2-mediated attenuation of origin licensing within both euchromatin and telomeric heterochromatin established the normal spatial distribution of origins across yeast chromosomes important for normal genome duplication.

T cells expressing the transcription factor PLZF regulate the development of memory-like CD8+ T cells.

Several gene-deficiency models promote the development of innate CD8(+) T cells that have diverse T cell antigen receptors (TCRs) but have a memory phenotype and rapidly produce cytokines. We demonstrate here that similar cells developed in mice deficient in the transcription factor KLF2. However, this was not due to intrinsic deficiency in KLF2 but instead was due to interleukin 4 (IL-4) produced by an expanded population of T cells expressing the transcription factor PLZF. The development of innate CD8(+) T cells in mice deficient in the tyrosine kinase Itk and coactivator CBP was also attributable to this IL-4-dependent mechanism. Finally, we show that the same mechanism drove the differentiation of innate CD8(+) T cells in BALB/c mice. Our findings identify a previously unknown mechanism of regulation of CD8(+) T cells via the production of IL-4 by PLZF(+) T cells.

Rif1 controls DNA replication by directing Protein Phosphatase 1 to reverse Cdc7-mediated phosphorylation of the MCM complex.

Initiation of eukaryotic DNA replication requires phosphorylation of the MCM complex by Dbf4-dependent kinase (DDK), composed of Cdc7 kinase and its activator, Dbf4. We report here that budding yeast Rif1 (Rap1-interacting factor 1) controls DNA replication genome-wide and describe how Rif1 opposes DDK function by directing Protein Phosphatase 1 (PP1)-mediated dephosphorylation of the MCM complex. Deleting RIF1 partially compensates for the limited DDK activity in a cdc7-1 mutant strain by allowing increased, premature phosphorylation of Mcm4. PP1 interaction motifs within the Rif1 N-terminal domain are critical for its repressive effect on replication. We confirm that Rif1 interacts with PP1 and that PP1 prevents premature Mcm4 phosphorylation. Remarkably, our results suggest that replication repression by Rif1 is itself also DDK-regulated through phosphorylation near the PP1-interacting motifs. Based on our findings, we propose that Rif1 is a novel PP1 substrate targeting subunit that counteracts DDK-mediated phosphorylation during replication. Fission yeast and mammalian Rif1 proteins have also been implicated in regulating DNA replication. Since PP1 interaction sites are evolutionarily conserved within the Rif1 sequence, it is likely that replication control by Rif1 through PP1 is a conserved mechanism.

Yeast heterochromatin regulators Sir2 and Sir3 act directly at euchromatic DNA replication origins.

Most active DNA replication origins are found within euchromatin, while origins within heterochromatin are often inactive or inhibited. In yeast, origin activity within heterochromatin is negatively controlled by the histone H4K16 deacetylase, Sir2, and at some heterochromatic loci also by the nucleosome binding protein, Sir3. The prevailing view has been that direct functions of Sir2 and Sir3 are confined to heterochromatin. However, growth defects in yeast mutants compromised for loading the MCM helicase, such as cdc6-4, are suppressed by deletion of either SIR2 or SIR3. While these and other observations indicate that SIR2,3 can have a negative impact on at least some euchromatic origins, the genomic scale of this effect was unknown. It was also unknown whether this suppression resulted from direct functions of Sir2,3 within euchromatin, or was an indirect effect of their previously established roles within heterochromatin. Using MCM ChIP-Seq, we show that a SIR2 deletion rescued MCM complex loading at ~80% of euchromatic origins in cdc6-4 cells. Therefore, Sir2 exhibited a pervasive effect at the majority of euchromatic origins. Using MNase-H4K16ac ChIP-Seq, we show that origin-adjacent nucleosomes were depleted for H4K16 acetylation in a SIR2-dependent manner in wild type (i.e. CDC6) cells. In addition, we present evidence that both Sir2 and Sir3 bound to nucleosomes adjacent to euchromatic origins. The relative levels of each of these molecular hallmarks of yeast heterochromatin-SIR2-dependent H4K16 hypoacetylation, Sir2, and Sir3 -correlated with how strongly a SIR2 deletion suppressed the MCM loading defect in cdc6-4 cells. Finally, a screen for histone H3 and H4 mutants that could suppress the cdc6-4 growth defect identified amino acids that map to a surface of the nucleosome important for Sir3 binding. We conclude that heterochromatin proteins directly modify the local chromatin environment of euchromatic DNA replication origins.

Hypomorphic caspase activation and recruitment domain 11 (CARD11) mutations associated with diverse immunologic phenotypes with or without atopic disease.

BACKGROUND: Caspase activation and recruitment domain 11 (CARD11) encodes a scaffold protein in lymphocytes that links antigen receptor engagement with downstream signaling to nuclear factor κB, c-Jun N-terminal kinase, and mechanistic target of rapamycin complex 1. Germline CARD11 mutations cause several distinct primary immune disorders in human subjects, including severe combined immune deficiency (biallelic null mutations), B-cell expansion with nuclear factor κB and T-cell anergy (heterozygous, gain-of-function mutations), and severe atopic disease (loss-of-function, heterozygous, dominant interfering mutations), which has focused attention on CARD11 mutations discovered by using whole-exome sequencing. OBJECTIVES: We sought to determine the molecular actions of an extended allelic series of CARD11 and to characterize the expanding range of clinical phenotypes associated with heterozygous CARD11 loss-of-function alleles. METHODS: Cell transfections and primary T-cell assays were used to evaluate signaling and function of CARD11 variants. RESULTS: Here we report on an expanded cohort of patients harboring novel heterozygous CARD11 mutations that extend beyond atopy to include other immunologic phenotypes not previously associated with CARD11 mutations. In addition to (and sometimes excluding) severe atopy, heterozygous missense and indel mutations in CARD11 presented with immunologic phenotypes similar to those observed in signal transducer and activator of transcription 3 loss of function, dedicator of cytokinesis 8 deficiency, common variable immunodeficiency, neutropenia, and immune dysregulation, polyendocrinopathy, enteropathy, X-linked-like syndrome. Pathogenic variants exhibited dominant negative activity and were largely confined to the CARD or coiled-coil domains of the CARD11 protein. CONCLUSION: These results illuminate a broader phenotypic spectrum associated with CARD11 mutations in human subjects and underscore the need for functional studies to demonstrate that rare gene variants encountered in expected and unexpected phenotypes must nonetheless be validated for pathogenic activity.

Bivalirudin versus heparin in patients undergoing percutaneous peripheral interventions: A systematic review and meta-analysis.

BACKGROUND: Bivalirudin may be an effective alternative anticoagulant to heparin for use in percutaneous peripheral interventions. We aimed to compare the safety and efficacy of bivalirudin versus heparin as the procedural anticoagulant agent in patients undergoing percutaneous peripheral intervention. METHODS: For this meta-analysis and systematic review, we conducted a search in PubMed, Medline, Embase, and Cochrane for all the clinical studies in which bivalirudin was compared to heparin as the procedural anticoagulant in percutaneous peripheral interventions. Outcomes studied included all-cause mortality, all-bleeding, major and minor bleeding, and access site complications. RESULTS: Eleven studies were included in the analysis, totaling 20,137 patients. There was a significant difference favoring bivalirudin over heparin for all-cause mortality (risk ratio 0.58, 95% CI 0.39-0.87), all-bleeding (risk ratio 0.62, 95% CI 0.50-0.78), major bleeding (risk ratio 0.61, 95% CI 0.39-0.96), minor bleeding (risk ratio 0.66, 95% CI 0.47-0.92), and access site complications (risk ratio 0.66, 95% CI 0.51-0.84). There was no significant difference in peri-procedural need for blood transfusions (risk ratio 0.79, 95% CI 0.57-1.08), myocardial infarction (risk ratio 0.87, 95% CI 0.59-1.28), stroke (risk ratio 0.77, 95% CI 0.59-1.01), intracranial bleeding (risk ratio 0.77, 95% CI 0.29-2.02), or amputations (OR 0.75, 95% CI 0.53-1.05). CONCLUSION: Our meta-analysis suggests that bivalirudin use for percutaneous peripheral interventions is associated with lower all-cause mortality, bleeding, and access site complications as compared to heparin. Further large randomized trials are needed to confirm the current results.

KLF2 transcription-factor deficiency in T cells results in unrestrained cytokine production and upregulation of bystander chemokine receptors.

The transcription factor KLF2 regulates T cell trafficking by promoting expression of the lipid-binding receptor S1P(1) and the selectin CD62L. Recently, it was proposed that KLF2 also represses the expression of chemokine receptors. We confirmed the upregulation of the chemokine receptor CXCR3 on KLF2-deficient T cells. However, we showed that this was a cell-nonautonomous effect, as revealed by CXCR3 upregulation on wild-type bystander cells in mixed bone-marrow chimeras with KLF2-deficient cells. Furthermore, KLF2-deficient T cells overproduced IL-4, leading to the upregulation of CXCR3 through an IL-4-receptor- and eomesodermin-dependent pathway. Consistent with the increased IL-4 production, we found high concentrations of serum IgE in mice with T cell-specific KLF2 deficiency. Our findings support a model where KLF2 regulates T cell trafficking by direct regulation of S1P(1) and CD62L and restrains spontaneous cytokine production in naive T cells.

The conserved bromo-adjacent homology domain of yeast Orc1 functions in the selection of DNA replication origins within chromatin.

The origin recognition complex (ORC) binds to the specific positions on chromosomes that serve as DNA replication origins. Although ORC is conserved from yeast to humans, the DNA sequence elements that specify ORC binding are not. In particular, metazoan ORC shows no obvious DNA sequence specificity, whereas yeast ORC binds to a specific DNA sequence within all yeast origins. Thus, whereas chromatin must play an important role in metazoan ORC's ability to recognize origins, it is unclear whether chromatin plays a role in yeast ORC's recognition of origins. This study focused on the role of the conserved N-terminal bromo-adjacent homology domain of yeast Orc1 (Orc1BAH). Recent studies indicate that BAH domains are chromatin-binding modules. We show that the Orc1BAH domain was necessary for ORC's stable association with yeast chromosomes, and was physiologically relevant to DNA replication in vivo. This replication role was separable from the Orc1BAH domain's previously defined role in transcriptional silencing. Genome-wide analyses of ORC binding in ORC1 and orc1bahDelta cells revealed that the Orc1BAH domain contributed to ORC's association with most yeast origins, including a class of origins highly dependent on the Orc1BAH domain for ORC association (orc1bahDelta-sensitive origins). Orc1bahDelta-sensitive origins required the Orc1BAH domain for normal activity on chromosomes and plasmids, and were associated with a distinct local nucleosome structure. These data provide molecular insights into how the Orc1BAH domain contributes to ORC's selection of replication origins, as well as new tools for examining conserved mechanisms governing ORC's selection of origins within eukaryotic chromosomes.

Bivalirudin versus heparin in patients undergoing percutaneous transcatheter aortic valve interventions: A systematic review and meta-analysis.

BACKGROUND: Bivalirudin may be an effective anticoagulation alternative to heparin as anticoagulant agent in percutaneous transcatheter aortic valve interventions (PAVI). We aimed to compare safety and efficacy of bivalirudin versus heparin as the procedural anticoagulant agent in patients undergoing PAVI. METHODS: We conducted an electronic database search of all published data. The primary efficacy endpoints were all-cause mortality, cardiovascular mortality, myocardial infarction, and stroke. Safety endpoints include major and life-threatening bleed according to VARC and BARC bleeding, blood transfusion, vascular complications, and acute kidney injury. Odds ratios (OR) and 95% confidence intervals (CI) computed using the Mantel-Haenszel method. RESULTS: Three studies (n = 1690 patients) were included, one randomized trial and two observational studies. There was a significant difference favoring bivalirudin over heparin for myocardial infarction (OR 0.41, 95%CI 0.20-0.87). There was no significant difference in all-cause mortality at 30 days (OR 0.97, 95%CI 0.62-1.52), cardiovascular mortality (OR 1.03, 95%CI 0.52-2.05), stroke (OR 1.23, 95%CI 0.62-2.46), vascular complications (OR 0.96, 95%CI 0.70-1.32), acute kidney injury (OR 1.03, 95%CI 0.53-2.00), blood transfusion (OR 0.67, 95% CI 0.45-1.01), major and life-threatening bleed (OR 0.74, 95%CI 0.37-1.49), and BARC bleeding (OR 0.52, 95%CI 0.23-1.18). CONCLUSIONS: In patient undergoing aortic valve interventions, no difference was seen between the use of bivalirudin and heparin as the procedural anticoagulant agent, except for a significant lower myocardial infarction events when bivalirudin was used. Further large randomized trials are needed to confirm current results.

An ARS element inhibits DNA replication through a SIR2-dependent mechanism.

During G1 phase, a prereplicative complex (pre-RC) that determines where DNA synthesis initiates forms at origins. The Sir2p histone deacetylase inhibits pre-RC assembly at a subset of origins, suggesting that Sir2p inhibits DNA replication through a unique aspect of origin structure. Here, we identified five SIR2-sensitive origins on chromosomes III and VI. Linker scan analysis of two origins indicated that they share a common organization, including an inhibitory sequence positioned 3' to the sites of origin recognition complex (ORC) binding and pre-RC assembly. This inhibitory sequence (I(S)) required SIR2 for its activity, suggesting that SIR2 inhibits origins through this sequence. Furthermore, I(S) elements occurred within positioned nucleosomes, and Abf1p-mediated exclusion of nucleosomes from the origin abrogated the inhibition. These data suggest that Sir2p and I(S) elements inhibit origin activity by promoting an unfavorable chromatin structure for pre-RC assembly.

Postselection thymocyte maturation and emigration are independent of IL-7 and ERK5.

The transcription factor Krüppel-like factor 2 (KLF2) controls the emigration of conventional T cells from the thymus through its regulation of the cell surface receptor S1P1. Prior to KLF2 expression, developing T cells require a positive selection signal through the TCR. However, following positive selection there are time, spatial, and maturational events that occur before KLF2 is finally upregulated and emigration occurs. We are interested in determining the signals that upregulate KLF2 and allow thymocytes to emigrate into circulation and whether they are linked to functional maturation. In endothelial cells KLF2 expression has been shown to be dependent on the mitogen-activated protein kinase ERK5. Furthermore, it has been reported that IL-7 signaling leads to the phosphorylation of ERK5. Thus, we hypothesized that IL-7R signaling through ERK5 could drive the expression of KLF2. In this study, we provide evidence that this hypothesis is incorrect. We also found that CD8 lineage specification occurred normally in the absence of IL-7R signaling, in contrast to a recently proposed model. We showed that both CD4 and CD8 T cells complete maturation and express KLF2 independently of ERK5 and IL-7.

Kruppel-like factor 2 is required for trafficking but not quiescence in postactivated T cells.

The transcription factor Kruppel-like factor 2 (KLF2) was proposed to regulate genes involved in cell cycle entry and T cell trafficking; however, the physiological role of its expression in postactivated T cells is not well defined. Previous studies suggested that the cytokines IL-2 and IL-15 differentially regulate KLF2 re-expression in postactivation T cells and that these cytokines also influence effector versus memory T cell differentiation. Using conditional and inducible KLF2-knockout model systems, we tested the specific role of KLF2 expression in activated CD8(+) T cells cultured with these cytokines. KLF2 was required for effective transcription of sphingosine-1-phosphate receptor-1 (S1P(1)) and CD62L in postactivation T cells. However, although different cytokines dramatically altered the expression of cell-cycle-related genes, endogenous KLF2 had a minimal impact. Correspondingly, KLF2-deficient T cells showed dysregulated trafficking but not altered proliferative characteristics following in vivo responses to Ag. Thus, our data help to define KLF2-dependent and -independent aspects of activated CD8(+) T cell differentiation and argue against a physiological role in cell cycle regulation.

High-resolution analysis of four efficient yeast replication origins reveals new insights into the ORC and putative MCM binding elements.

In budding yeast, the eukaryotic initiator protein ORC (origin recognition complex) binds to a bipartite sequence consisting of an 11 bp ACS element and an adjacent B1 element. However, the genome contains many more matches to this consensus than actually bind ORC or function as origins in vivo. Although ORC-dependent loading of the replicative MCM helicase at origins is enhanced by a distal B2 element, less is known about this element. Here, we analyzed four highly active origins (ARS309, ARS319, ARS606 and ARS607) by linker scanning mutagenesis and found that sequences adjacent to the ACS contributed substantially to origin activity and ORC binding. Using the sequences of four additional B2 elements we generated a B2 multiple sequence alignment and identified a shared, degenerate 8 bp sequence that was enriched within 228 known origins. In addition, our high-resolution analysis revealed that not all origins exist within nucleosome free regions: a class of Sir2-regulated origins has a stably positioned nucleosome overlapping or near B2. This study illustrates the conserved yet flexible nature of yeast origin architecture to promote ORC binding and origin activity, and helps explain why a strong match to the ORC binding site is insufficient to identify origins within the genome.

Krüppel-like factor 2 regulates trafficking and homeostasis of gammadelta T cells.

gammadelta T cells are generated in the thymus and traffic to secondary lymphoid organs and epithelial surfaces, where they regulate immune responses. alphabeta T cells require sphingosine 1-phosphate receptor type 1 (S1P(1)) and CD62L for thymic emigration and circulation through secondary lymphoid organs. Both of these genes are regulated by the transcription factor Krüppel-like factor 2 (KLF2) in conventional alphabeta T cells. It is unclear if gammadelta T cells use similar mechanisms. In this study, we show that thymic gammadelta T cells express S1P(1) and that it is regulated by KLF2. Furthermore, KLF2 and S1P(1)-deficient gammadelta T cells accumulate in the thymus and fail to populate the secondary lymphoid organs or gut, in contrast to the expectation from published work. Interestingly, KLF2 but not S1P(1) deficiency led to the expansion of a usually rare population of CD4(+) promyelocytic leukemia zinc finger(+) "gammadelta NKT" cells. Thus, KLF2 is critically important for the homeostasis and trafficking of gammadelta T cells.

Kruppel-like factor 2 regulates thymocyte and T-cell migration.

Mammalian Kruppel-like transcription factors are implicated in regulating terminal differentiation of several tissue types. Deficiency in Kruppel-like factor (KLF) 2 (also known as LKLF) leads to a massive loss of the peripheral T-cell pool, suggesting KLF2 regulates T-cell quiescence and survival. Here we show, however, that KLF2 is essential for T-cell trafficking. KLF2-deficient (Klf2-/-) thymocytes show impaired expression of several receptors required for thymocyte emigration and peripheral trafficking, including the sphingosine-1-phosphate (S1P) receptor S1P1, CD62L and beta7 integrin. Furthermore, KLF2 both binds and transactivates the promoter for S1P1--a receptor that is critical for thymocyte egress and recirculation through peripheral lymphoid organs. Our findings suggest that KLF2 serves to license mature T cells for trafficking from the thymus and recirculation through secondary lymphoid tissues.