DIDO is necessary for the adipogenesis that promotes diet-induced obesity

The prevalence of overweight and obesity continues to rise in the population worldwide. Because it is an important predisposing factor for cancer, cardiovascular diseases, diabetes mellitus, and COVID-19, obesity reduces life expectancy. Adipose tissue (AT), the main fat storage organ with endocrine capacity, plays fundamental roles in systemic metabolism and obesity-related diseases. Dysfunctional AT can induce excess or reduced body fat (lipodystrophy). Dido1 is a marker gene for stemness; gene-targeting experiments compromised several functions ranging from cell division to embryonic stem cell differentiation, both in vivo and in vitro. We report that mutant mice lacking the DIDO N terminus show a lean phenotype. This consists of reduced AT and hypolipidemia, even when mice are fed a high-nutrient diet. DIDO mutation caused hypothermia due to lipoatrophy of white adipose tissue (WAT) and dermal fat thinning. Deep sequencing of the epididymal white fat (Epi WAT) transcriptome supported Dido1 control of the cellular lipid metabolic process. We found that, by controlling the expression of transcription factors such as C/EBPα or PPARγ, Dido1 is necessary for adipocyte differentiation, and that restoring their expression reestablished adipogenesis capacity in Dido1 mutants. Our model differs from other lipodystrophic mice and could constitute a new system for the development of therapeutic intervention in obesity.

PARP1, DIDO3, and DHX9 Proteins Mutually Interact in Mouse Fibroblasts, with Effects on DNA Replication Dynamics, Senescence, and Oncogenic Transformation

The regulated formation and resolution of R-loops is a natural process in physiological gene expression. Defects in R-loop metabolism can lead to DNA replication stress, which is associated with a variety of diseases and, ultimately, with cancer. The proteins PARP1, DIDO3, and DHX9 are important players in R-loop regulation. We previously described the interaction between DIDO3 and DHX9. Here, we show that, in mouse embryonic fibroblasts, the three proteins are physically linked and dependent on PARP1 activity. The C-terminal truncation of DIDO3 leads to the impairment of this interaction; concomitantly, the cells show increased replication stress and senescence. DIDO3 truncation also renders the cells partially resistant to in vitro oncogenic transformation, an effect that can be reversed by immortalization. We propose that PARP1, DIDO3, and DHX9 proteins form a ternary complex that regulates R-loop metabolism, preventing DNA replication stress and subsequent senescence.

Hepatitis, testicular degeneration, and ataxia in DIDO3-deficient mice with altered mRNA processing

Background

mRNA processing is an essential step of gene expression; its malfunction can lead to different degrees of physiological disorder from subclinical disease to death. We previously identified Dido1 as a stemness marker and a gene involved in embryonic stem cell differentiation. DIDO3, the largest protein encoded by the Dido1 gene, is necessary for accurate mRNA splicing and correct transcription termination. The deletion of Dido1 exon16, which encodes the carboxy-terminal half of DIDO3, results in early embryonic lethality in mouse.

Results

We obtained mice bearing a Cre-LoxP conditional version of that deletion and studied the effects of inducing it ubiquitously in adult stages. DIDO3-deficient mice survive the deletion but suffer mild hepatitis, testicular degeneration, and progressive ataxia, in association with systemic alterations in mRNA splicing and transcriptional readthrough.

Conclusions

These results offer insight into the distinct vulnerabilities in mouse organs following impairment of the mRNA processing machinery, and could aid understanding of human health dependence on accurate mRNA metabolism.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13578-022-00804-8.

Interplay between splicing and transcriptional pausing exerts genome-wide control over alternative polyadenylation

Recent studies have identified multiple polyadenylation sites in nearly all mammalian genes. Although these are interpreted as evidence for alternative polyadenylation, our knowledge of the underlying mechanisms is still limited. Most studies only consider the immediate surroundings of gene ends, even though in vitro experiments have uncovered the involvement of external factors such as splicing. Whereas in vivo splicing manipulation was impracticable until recently, we now used mutants in the Death Inducer Obliterator (DIDO) gene to study their impact on 3ʹ end processing. We observe multiple rounds of readthrough and gene fusions, suggesting that no arbitration between polyadenylation sites occurs. Instead, a window of opportunity seems to control end processing. Through the identification of T-rich sequence motifs, our data indicate that splicing and transcriptional pausing interact to regulate alternative polyadenylation. We propose that 3ʹ splice site activation comprises a variable timer, which determines how long transcription proceeds before polyadenylation signals are recognized. Thus, the role of core polyadenylation signals could be more passive than commonly believed. Our results provide new insights into the mechanisms of alternative polyadenylation and expand the catalog of related aberrations.

Abbreviations APA: alternative polyadenylation; bp: basepair; MEF: mouse embryonic fibroblasts; PA: polyadenylation; PAS: polyadenylation site; Pol II: (RNA) polymerase II ; RT-PCR:reverse-transcriptase PCR; SF:splicing factor; SFPQ:splicing factor rich in proline and glutamine; SS:splice site; TRSM:Thymidine rich sequence motif; UTR:untranslated terminal region

Impaired stem cell differentiation and somatic cell reprogramming in DIDO3 mutants with altered RNA processing and increased R-loop levels

Embryonic stem cell (ESC) differentiation and somatic cell reprogramming are biological processes governed by antagonistic expression or repression of a largely common set of genes. Accurate regulation of gene expression is thus essential for both processes, and alterations in RNA processing are predicted to negatively affect both. We show that truncation of the DIDO gene alters RNA splicing and transcription termination in ESC and mouse embryo fibroblasts (MEF), which affects genes involved in both differentiation and reprogramming. We combined transcriptomic, protein interaction, and cellular studies to identify the underlying molecular mechanism. We found that DIDO3 interacts with the helicase DHX9, which is involved in R-loop processing and transcription termination, and that DIDO3-exon16 deletion increases nuclear R-loop content and causes DNA replication stress. Overall, these defects result in failure of ESC to differentiate and of MEF to be reprogrammed. MEF immortalization restored impaired reprogramming capacity. We conclude that DIDO3 has essential functions in ESC differentiation and somatic cell reprogramming by supporting accurate RNA metabolism, with its exon16-encoded domain playing the main role.

Linking stem cells to chromosomal instability

The discovery of a stem cell population in human neoplasias has given a new impulse to the study of the origins of cancer. The tissue compartment in which transformation first occurs likely comprises stem cells, since these cells need to consolidate the short-term and long-term requisites of tissue renewal. Because of their unique role, stem cells have a combination of characteristics that makes them susceptible to genetic damage, transformation, and tumor initiation. One type of genetic damage in particular, chromosomal instability, might affect the stem cell compartment, because it induces an ongoing cycle of DNA damage and alters cellular programming. Here, we will discuss some of the recently described links between SC, chromosomal instability, and carcinogenesis, and outline some of the consequences for oncoimmunology.

Growth Hormone Reprograms Macrophages toward an Anti-Inflammatory and Reparative Profile in an MAFB-Dependent Manner

Growth hormone (GH), a pleiotropic hormone secreted by the pituitary gland, regulates immune and inflammatory responses. In this study, we show that GH regulates the phenotypic and functional plasticity of macrophages both in vitro and in vivo. Specifically, GH treatment of GM-CSF-primed monocyte-derived macrophages promotes a significant enrichment of anti-inflammatory genes and dampens the proinflammatory cytokine profile through PI3K-mediated downregulation of activin A and upregulation of MAFB, a critical transcription factor for anti-inflammatory polarization of human macrophages. These in vitro data correlate with improved remission of inflammation and mucosal repair during recovery in the acute dextran sodium sulfate-induced colitis model in GH-overexpressing mice. In this model, in addition to the GH-mediated effects on other immune cells, we observed that macrophages from inflamed gut acquire an anti-inflammatory/reparative profile. Overall, these data indicate that GH reprograms inflammatory macrophages to an anti-inflammatory phenotype and improves resolution during pathologic inflammatory responses.

Dido3-dependent SFPQ recruitment maintains efficiency in mammalian alternative splicing

Alternative splicing is facilitated by accessory proteins that guide spliceosome subunits to the primary transcript. Many of these splicing factors recognize the RNA polymerase II tail, but SFPQ is a notable exception even though essential for mammalian RNA processing. This study reveals a novel role for Dido3, one of three Dido gene products, in alternative splicing. Binding of the Dido3 amino terminus to histones and to the polymerase jaw domain was previously reported, and here we show interaction between its carboxy terminus and SFPQ. We generated a mutant that eliminates Dido3 but preserves other Dido gene products, mimicking reduced Dido3 levels in myeloid neoplasms. Dido mutation suppressed SFPQ binding to RNA and increased skipping for a large group of exons. Exons bearing recognition sequences for alternative splicing factors were nonetheless included more efficiently. Reduced SFPQ recruitment may thus account for increased skipping of SFPQ-dependent exons, but could also generate a splicing factor surplus that becomes available to competing splice sites. Taken together, our data indicate that Dido3 is an adaptor that controls SFPQ utilization in RNA splicing. Distributing splicing factor recruitment over parallel pathways provides mammals with a simple mechanism to regulate exon usage while maintaining RNA splicing efficiency.

Inhibitory Role of Growth Hormone in the Induction and Progression Phases of Collagen-Induced Arthritis

Evidence indicates an intimate connection between the neuroendocrine and the immune systems. A number of in vitro and in vivo studies have demonstrated growth hormone (GH) involvement in immune regulation. The GH receptor is expressed by several leukocyte subpopulations, and GH modulates immune cell proliferation and activity. Here, we found that sustained GH expression protected against collagen-induced arthritis (CIA); in GH-transgenic C57BL/6 (GHTg) mice, disease onset was delayed, and its overall severity was decreased. The anti-collagen response was impaired in these mice, as were inflammatory cytokine levels. Compared to control arthritic littermates, immunized GHTg mice showed significantly lower RORγt (retinoic acid receptor-related orphan receptor gamma 2), IL-17, GM-CSF, IL-22, and IFNγ mRNA expression in draining lymph nodes, whereas there were no differences in IL-21, IL-6, or IL-2 mRNA levels. Data thus suggest that Th17/Th1 cell plasticity toward a pathological phenotype is reduced in these mice. Exogenous GH administration in arthritic DBA/1J mice reduced the severity of established CIA as well as the inflammatory environment, which also shows a GH effect on arthritis progression. These results indicate that GH prevents inflammatory joint destruction in CIA. Our findings demonstrate a modulatory GH role in immune system function that contributes to alleviating CIA symptoms and underlines the importance of endocrine regulation of the immune response.

p38α regulates cytokine-induced IFNγ secretion via the Mnk1/eIF4E pathway in Th1 cells

The p38 mitogen-activated protein kinase (MAPK) pathway is involved in the regulation of immune and inflammatory processes. We used p38α-conditional, p38β-deficient and p38α/β double-null mouse models to address the role of these two p38 MAPK in CD4⁺ T cells, and found that p38α deficiency causes these cells to hyperproliferate. Our studies indicate that both p38α and p38β are dispensable for T helper cell type 1 (Th1) differentiation but, by controlling interferon (IFN)γ and tumor necrosis factor (TNF)α production, are critical for normal Th1 effector function. We found that both p38α and p38β modulate T-cell receptor-induced IFNγ and TNFα production, whereas only p38α regulates cytokine-induced IFNγ production. The lack of p38α and p38β did not affect transcription and mRNA stability of Ifng. However, the absence of p38α in Th1 cells resulted in a decreased MNK1 phosphorylation after cytokine activation, and MNK1 inhibition blocked IFNγ production. Our results indicate that p38α regulates IFNγ secretion through the activation of the MNK1/eIF4E pathway of translation initiation and identify specific functions for p38α and p38β in T-cell proliferation.

The Role of IFN-β during the Course of Sepsis Progression and Its Therapeutic Potential

Sepsis is a complex biphasic syndrome characterized by both pro- and anti-inflammatory immune states. Whereas early sepsis mortality is caused by an acute, deleterious pro-inflammatory response, the second sepsis phase is governed by acute immunosuppression, which predisposes patients to long-term risk for life-threatening secondary infections. Despite extensive basic research and clinical trials, there is to date no specific therapy for sepsis, and mortality rates are on the rise. Although IFN-β is one of the most-studied cytokines, its diverse effects are not fully understood. Depending on the disease or type of infection, it can have beneficial or detrimental effects. As IFN-β has been used successfully to treat diverse diseases, emphasis has been placed on understanding the role of IFN-β in sepsis. Analyses of mouse models of septic shock attribute a pro-inflammatory role to IFN-β in sepsis development. As anti-inflammatory treatments in humans with antibodies to TNF-α or IL1-β resulted disappointing, cytokine modulation approaches were discouraged and neutralization of IFN-β has not been pursued for sepsis treatment. In the case of patients with delayed sepsis and immunosuppression, there is a debate as to whether the use of specific cytokines would restore the deactivated immune response. Recent reports show an association of low IFN-β levels with the hyporesponsive state of monocytes from sepsis patients and after endotoxin tolerance induction. These data, discussed here, project a role for IFN-β in restoring monocyte function and reversing immunosuppression, and suggest IFN-β-based additive immunomodulatory therapy. The dichotomy in putative therapeutic approaches, involving reduction or an increase in IFN-β levels, mirrors the contrasting nature of the early hyperinflammatory state and the delayed immunosuppression phase.

On How Fas Apoptosis-Independent Pathways Drive T Cell Hyperproliferation and Lymphadenopathy in lpr Mice

Fas induces massive apoptosis in T cells after repeated in vitro T cell receptor (TCR) stimulation and is critical for lymphocyte homeostasis in Fas-deficient (lpr) mice. Although the in vitro Fas apoptotic mechanism has been defined, there is a large conceptual gap between this in vitro phenomenon and the pathway that leads to in vivo development of lymphadenopathy and autoimmunity. A striking abnormality in lpr mice is the excessive proliferation of CD4⁺ and CD8⁺ T cells, and more so of the double-negative TCR⁺CD4⁻CD8⁻B220⁺ T cells. The basis of lpr T cell hyperproliferation remains elusive, as it cannot be explained by Fas-deficient apoptosis. T cell-directed p21 overexpression reduces hyperactivation/hyperproliferation of all lpr T cell subtypes and lymphadenopathy in lpr mice. p21 controls expansion of repeatedly stimulated T cells without affecting apoptosis. These results confirm a direct link between hyperactivation/hyperproliferation, autoreactivity, and lymphadenopathy in lpr mice and, with earlier studies, suggest that Fas apoptosis-independent pathways control lpr T cell hyperproliferation. lpr T cell hyperproliferation could be an indirect result of the defective apoptosis of repeatedly stimulated lpr T cells. Nonetheless, in this perspective, we argue for an alternative setting, in which lack of Fas would directly cause lpr T cell hyperactivation/hyperproliferation in vivo. We propose that Fas/Fas ligand (FasL) acts as an activation inhibitor of recurrently stimulated T cells, and that its disruption causes overexpansion of T cells in lpr mice. Research to define the underlying mechanism of this Fas/FasL effect could resolve the phenotype of lpr mice and lead to therapeutics for related human syndromes.

p21 mediates macrophage reprogramming through regulation of p50-p50 NF-κB and IFN-β

M1 and M2 macrophage phenotypes, which mediate proinflammatory and antiinflammatory functions, respectively, represent the extremes of immunoregulatory plasticity in the macrophage population. This plasticity can also result in intermediate macrophage states that support a balance between these opposing functions. In sepsis, M1 macrophages can compensate for hyperinflammation by acquiring an M2-like immunosuppressed status that increases the risk of secondary infection and death. The M1 to M2 macrophage reprogramming that develops during LPS tolerance resembles the pathological antiinflammatory response to sepsis. Here, we determined that p21 regulates macrophage reprogramming by shifting the balance between active p65-p50 and inhibitory p50-p50 NF-κB pathways. p21 deficiency reduced the DNA-binding affinity of the p50-p50 homodimer in LPS-primed and -rechallenged macrophages, impairing their ability to attenuate IFN-β production and acquire an M2-like hyporesponsive status. High p21 levels in sepsis patients correlated with low IFN-β expression, and p21 knockdown in human monocytes corroborated its role in IFN-β regulation. The data demonstrate that p21 adjusts the equilibrium between p65-p50 and p50-p50 NF-κB pathways to mediate macrophage plasticity in LPS tolerance. Identifying p21-related pathways involved in monocyte reprogramming may lead to potential targets for sepsis treatment.

The expression of Death Inducer-Obliterator (DIDO) variants in Myeloproliferative Neoplasms

Chronic Myeloid Leukemia (CML), Polycythemia Vera (PV), Essential Thrombocythemia (ET) and Primary Myelofibrosis (PMF) are Myeloproliferative Neoplasms (MPN) characterized by clonal myeloproliferation without cell maturation impairment. CML pathogenesis is associated with the Ph chromosome leading to BCR-ABL tyrosine-kinase constitutive expression. The Ph negative MPN (PV, ET and PMF) are characterized by the mutation JAK2(V617F) of the JAK2 protein in the auto-inhibitory JH2 domain, which is found in most PV patients and in approximately half of ET and PMF patients. Considerable effort is being made to understand the role of JAK2(V617F) at the MPN initiation and to clarify the pathogenesis and apoptosis resistance in CML, PV, ET and PMF patients. In the present investigation, we evaluated the Death Inducer-Obliterator (DIDO) (variants DIDO 1, 2 and 3) levels in CML, PV, ET and PMF patients. Our data reported the DIDO 1, 2 and 3 differential expressions in Myeloproliferative Neoplasms.

p21 suppresses autoimmunity by regulating ERK1/2 phosphorylation, NF-κB activation and IFNγ production in hyperactivated T cells (BA4P.141)

Peripheral tolerance is essential for suppressing autoimmunity and depends on the regulation of T cell activation, proliferation and apoptosis. p21, known originally as a cell cycle inhibitor, is implicated in effector/memory T cell responses and is considered a suppressor of lupus-like autoimmunity. However, the mechanism by which p21 regulates T cell responses and autoimmunity remains unknown. We investigated these questions by studying T cells of C57BL/6 p21-/- and C57BL/6-lpr p21-/- mice. p21 regulated activation of repeatedly stimulated effector/memory T cells in a cell cycle-independent manner, but had no effect on naïve T cells. We identified a previously non-described role for p21, in controlling T cell activation via downstream MAPK and NF-κB pathways in the cytoplasm. Lack of p21 caused hyperactivation of ERK1/2 and NF-κB in reactivated T cells. Importantly, p21-deficiency led to increased IFNγ production due to an effect of p21 on the IL-12- and IL-18-dependent IFNγ induction. Stimulation of TCR-transgenic T cells with specific antigens in vivo confirmed that p21 is involved in effector/memory T cell activation. Lack of p21 dramatically increased the mild lupus symptoms of C57BL/6-lpr mice to full-blown disease and death in C57BL/6-lpr p21-/- mice. The mechanism by which p21 regulates disease severity was based on its control of T cell activation and IFNγ production. Analysis of these p21 functions might be of therapeutic value for Lupus.

LPS-induced p21 is required for M2 polarization of endotoxin- tolerant macrophages and controls the accumulation of inhibitory p50/p50 NF-κB (INC6P.317)

Gram-negative bacterial infection can lead to systemic inflammation and sepsis — a complex pathology that is the third leading cause of death in the U.S. A critical mechanism in lowering inflammation and septic shock is endotoxin tolerance, a state of hyporesponsiveness to secondary lipopolysaccharide (LPS) challenge. p21 controls macrophage activation independently of its cell cycle inhibitor activity. Here, we investigated M1 to M2 macrophage polarization during endotoxin tolerance, which is regulated by NF-κB composition switch from p65/p50 to p50/p50. p21 deficiency led to delayed formation of inhibitory p50/p50 NF-κB homodimers that control IFN-β promoter, a key cytokine which orchestrates M1 responses. Consequently, lack of p21 enhanced IFN-β production and IFN-β-dependent STAT1 phosphorylation, resulting in upregulation of iNOS and M1 chemokines. Importantly, p21-deficient macrophages had impaired ability to acquire M2-like LPS-tolerant profile, showing reduced induction of M2 genes such as arginase I. The biological significance of our work was reflected in an in vivo model of endotoxin tolerance, where p21-deficient mice failed to develop tolerance and showed high M1-dependent responses and death. Overall, we identified p21 as a key molecule that regulates M2 polarization and endotoxin tolerance, through NF-κB composition switch from p65/p50 to p50/p50. Thus, analysis of the role of p21 in macrophages may be of therapeutic value for optimizing M1/M2 ratio in disease.

Distinct p21 requirements for regulating normal and self-reactive T cells through IFN-γ production

Self/non-self discrimination characterizes immunity and allows responses against pathogens but not self-antigens. Understanding the principles that govern this process is essential for designing autoimmunity treatments. p21 is thought to attenuate autoreactivity by limiting T cell expansion. Here, we provide direct evidence for a p21 role in controlling autoimmune T cell autoreactivity without affecting normal T cell responses. We studied C57BL/6, C57BL/6/lpr and MRL/lpr mice overexpressing p21 in T cells, and showed reduced autoreactivity and lymphadenopathy in C57BL/6/lpr, and reduced mortality in MRL/lpr mice. p21 inhibited effector/memory CD4(+) CD8(+) and CD4(-)CD8(-) lpr T cell accumulation without altering defective lpr apoptosis. This was mediated by a previously non-described p21 function in limiting T cell overactivation and overproduction of IFN-γ, a key lupus cytokine. p21 did not affect normal T cell responses, revealing differential p21 requirements for autoreactive and normal T cell activity regulation. The underlying concept of these findings suggests potential treatments for lupus and autoimmune lymphoproliferative syndrome, without compromising normal immunity.

Notch activation stimulates migration of breast cancer cells and promotes tumor growth

INTRODUCTION

Dysregulated NOTCH receptor activity has been implicated in breast cancer but the mechanisms by which NOTCH contributes to transformation are not yet clear, as it has context-dependent effects on the properties of transformed cells.

METHODS

We have used various in vitro and in vivo carcinogenic models to analyze the impact of Notch signaling in the onset and progression of breast tumors.

RESULTS

We found that ectopic expression of the Notch1 intracellular domain (N1ICD) in MCF-7 breast adenocarcinoma cell line caused reduction and delocalization of E-CADHERIN levels and increased migratory and invasive abilities. Notch inhibition in the invasive breast cancer cell line MDA-MB-231 resulted in increased E-CADHERIN expression and a parallel reduction in their invasive capacity. The growth of subcutaneous xenografts produced with MCF-7 cells was boosted after N1ICD induction, in a cell autonomous manner. In vivo Notch1 activation in the mammary gland using the MMTV-Cre driver caused the formation of papillary tumors that showed increased Hes1 and Hey1 expression and delocalized E-cadherin staining.

CONCLUSIONS

These results confirm NOTCH1 as a signal triggering epithelial-mesenchymal transition in epithelial cancer cells, which may have implications in tumor dissemination, metastasis and proliferation in vivo. The identification of specific factors interacting with NOTCH signaling could thus be relevant to fully understanding the role of NOTCH in breast neoplasia.

Antitumor effects of a monoclonal antibody to human CCR9 in leukemia cell xenografts

Tumor expression of certain chemokine receptors is associated with resistance to apoptosis, migration, invasiveness and metastasis. Because CCR9 chemokine receptor expression is very restricted in healthy tissue, whereas it is present in tumors of distinct origins including leukemias, melanomas, prostate and ovary carcinomas, it can be considered a suitable candidate for target-directed therapy. Here, we report the generation and characterization of 91R, a mouse anti-human CCR9 IgG2b monoclonal antibody that recognizes an epitope within the CCR9 N-terminal domain. This antibody inhibits the growth of subcutaneous xenografts from human acute T lymphoblastic leukemia MOLT-4 cells in immunodeficient Rag2^−/− mice. Tumor size in 91R-treated mice was reduced by 85% compared with isotype-matched antibody-treated controls. Tumor reduction in 91R-treated mice was concomitant with an increase in the apoptotic cell fraction and tumor necrotic areas, as well as a decrease in the fraction of proliferating cells and in tumor vascularization. In the presence of complement or murine natural killer cells, 91R promoted in vitro lysis of MOLT-4 leukemia cells, indicating that this antibody might eliminate tumor cells via complement- and cell-dependent cytotoxicity. The results show the potential of the 91R monoclonal antibody as a therapeutic agent for treatment of CCR9-expressing tumors.

Distinctive patterns of naïve/memory subset distribution and cytokine expression in CD4 T lymphocytes in ZAP-70 B-chronic lymphocytic patients

BACKGROUND

ZAP-70 upregulation in B chronic lymphocytic leukemia (B-CLL) cells is a recognized marker of poor prognosis in these patients; the biological basis of this differential clinical outcome nonetheless remains unknown. ZAP-70 overexpression is considered a surrogate marker of a B-CLL cell subset. To test whether the differential biological characteristics of these patients also include the T helper population, we studied naïve, non-terminated memory (NTEM), terminated memory (TEM) and central memory (CM) cells, and cytokine expression by CD4 T lymphocytes from ZAP-70(+) and ZAP-70(-) B-CLL patients.

METHODS

Expression of CD3, CD8, CD45RA, CD27, and CD28 antigens and intracytoplasmic cytokine production (IFNγ, IL-2, IL-4, IL-10, and TNFα) were assessed simultaneously by nine-color flow-cytometry in peripheral blood lymphocytes from B-CLL patients. B cell ZAP-70 expression in B-CLL cells was also analyzed by flow cytometry.

RESULTS

Compared to ZAP-70(-) B-CLL patients, ZAP-70(+) B-CLL patients showed 1) significant reduction in the naïve T helper subset and expansion of NTEM and TEM subsets, 2) a decrease in the percentage of activated CD4 T lymphocytes expressing IFNγ, TNFα, and IL-2, and 3) an increase in the percentage of CD4 T lymphocytes expressing IL-4 or IL-10.

CONCLUSIONS

In conclusion, in early stage B-CLL patients, ZAP-70 upregulation is associated with distinct patterns of activation/differentiation stage subset distribution and of cytokine expression in CD4 T lymphocytes.

Distinctive patterns of naïve/memory subset distribution and cytokine expression in CD4 T lymphocytes in ZAP-70 B-chronic lymphocytic patients

BACKGROUND

ZAP-70 upregulation in B chronic lymphocytic leukemia (B-CLL) cells is a recognized marker of poor prognosis in these patients; the biological basis of this differential clinical outcome nonetheless remains unknown. ZAP-70 overexpression is considered a surrogate marker of a B-CLL cell subset. To test whether the differential biological characteristics of these patients also include the T helper population, we studied naïve, non-terminated memory (NTEM), terminated memory (TEM) and central memory (CM) cells and cytokine expression by CD4 T lymphocytes from ZAP-70+ and ZAP-70- B-CLL patients.

METHODS

Expression of CD3, CD8, CD45RA, CD27, and CD28 antigens and intracytoplasmic cytokine production (IFNγ, IL-2, IL-4, IL-10 and TNFα) were assessed simultaneously by nine-color flow-cytometry in peripheral blood lymphocytes from B-CLL patients. B cell ZAP-70 expression in B-CLL cells was also analyzed by flow cytometry.

RESULTS

Compared to ZAP-70- B-CLL patients, ZAP-70+ B-CLL patients showed 1) significant reduction in the naïve T helper subset and expansion of NTEM and TEM subsets, 2) a decrease in the percentage of activated CD4 T lymphocytes expressing IFNγ, TNFα and IL-2, and 3) an increase in the percentage of CD4 T lymphocytes expressing IL-4 or IL-10.

CONCLUSIONS

In conclusion, in early stage B-CLL patients, ZAP-70 upregulation is associated with distinct patterns of activation/differentiation stage subset distribution and of cytokine expression in CD4 T lymphocytes. © 2013 Clinical Cytometry Society.

Dido3 PHD modulates cell differentiation and division

Death Inducer Obliterator 3 (Dido3) is implicated in the maintenance of stem cell genomic stability and tumorigenesis. Here, we show that Dido3 regulates the expression of stemness genes in embryonic stem cells through its plant homeodomain (PHD) finger. Binding of Dido3 PHD to histone H3K4me3 is disrupted by threonine phosphorylation that triggers Dido3 translocation from chromatin to the mitotic spindle. The crystal structure of Dido3 PHD in complex with H3K4me3 reveals an atypical aromatic-cage-like binding site that contains a histidine residue. Biochemical, structural, and mutational analyses of the binding mechanism identified the determinants of specificity and affinity and explained the inability of homologous PHF3 to bind H3K4me3. Together, our findings reveal a link between the transcriptional control in embryonic development and regulation of cell division.

Chromothripsis: breakage-fusion-bridge over and over again

The acquisition of massive but localized chromosome translocations, a phenomenon termed chromothripsis, has received widespread attention since its discovery over a year ago. Until recently, chromothripsis was believed to originate from a single catastrophic event, but the molecular mechanisms leading to this event are yet to be uncovered. Because a thorough interpretation of the data are missing, the phenomenon itself has wrongly acquired the status of a mechanism used to justify many kinds of complex rearrangements. Although the assumption that all translocations in chromothripsis originate from a single event has met with criticism, satisfactory explanations for the intense but localized nature of this phenomenon are still missing. Here, we show why the data used to describe massive catastrophic rearrangements are incompatible with a model comprising a single event only and propose a molecular mechanism in which a combination of known cellular pathways accounts for chromothripsis. Instead of a single traumatic event, the protection of undamaged chromosomes by telomeres can limit repetitive breakage-fusion-bridge events to a single chromosome arm. Ultimately, common properties of chromosomal instability, such as aneuploidy and centromere fission, might establish the complex genetic pattern observed in this genomic state.

Chemokine receptor oligomerization: a further step toward chemokine function

A broad array of biological responses including cell polarization, movement, immune and inflammatory responses, as well as prevention of HIV-1 infection, are triggered by the chemokines, a family of secreted and structurally related chemoattractant proteins that bind to class A-specific seven-transmembrane receptors linked to G proteins. Chemokines and their receptors should not be considered isolated entities, as they act in complex networks. Chemokines bind as oligomers, or oligomerize after binding to glycosaminoglycans on endothelial cells, and are then presented to their receptors on target cells, facilitating the generation of chemoattractant gradients. The chemokine receptors form homo- and heterodimers, as well as higher order structures at the cell surface. These structures are dynamic and are regulated by receptor expression and ligand levels. Complexity is even greater, as in addition to regulation by cytokines and decoy receptors, chemokine and receptor levels are affected by proteolytic cleavage and other protein modifications. This complex scenario should be considered when analyzing chemokine biology and the ability of their antagonists to act in vivo. Strategies based on blocking or stabilizing ligand and receptor dimers could be alternative approaches that might have broad therapeutic potential.

Drug testing in cellular chemotaxis assays

Described in this unit are methods for measuring the cell migration process. While cell adhesion protocols allow study of migrating cell interactions with the endothelial matrix, cellular migration assays permit analysis of directed cell movement towards a chemotactic gradient, both in vivo and in vitro. An in vitro cell invasion protocol is provided for analysis of the sum of the cell adhesion, migration, and invasion activities involved in tumor cell motility.

Tyr³²³-dependent p38 activation is associated with rheumatoid arthritis and correlates with disease activity

OBJECTIVE

The p38 MAPK is important in the pathogenic immune response in rheumatoid arthritis (RA). The p38 molecule can be activated through phosphorylation on Thr¹⁸⁰-Tyr¹⁸² by upstream MAPK kinases and via an alternative pathway through phosphorylation on Tyr³²³. We undertook this study to quantify the phosphorylation of Tyr³²³ p38 and of Thr¹⁸⁰-Tyr¹⁸² p38 on T cells from healthy controls and patients with RA or ankylosing spondylitis (AS) to identify variables associated with p38 phosphorylation and disease activity.

METHODS

We measured p38 phosphorylation on Tyr³²³ and Thr¹⁸⁰-Tyr¹⁸² by flow cytometry and Western blotting on T cells from 30 control subjects, 33 AS patients, 30 patients with RA in remission, and 79 patients with active RA. We collected the clinical characteristics and analyzed correlations between clinical variables, the Disease Activity Score in 28 joints (DAS28), and p38 phosphorylation levels. Multivariate regression analysis was performed to identify variables associated with p38 phosphorylation on Tyr³²³ and Thr¹⁸⁰-Tyr¹⁸².

RESULTS

Phosphorylation of p38 on Tyr³²³ was higher in T cells from patients with active RA (P = 0.008 versus healthy controls) than in patients with RA in remission or in patients with AS. Tyr³²³ p38 phosphorylation was associated with disease activity determined by the DAS28 (P = 0.017). Enhanced p38 phosphorylation was linked to Lck-mediated activation of the Tyr³²³-dependent pathway in the absence of upstream MAPKK activation.

CONCLUSION

Our results indicate that phosphorylation status on Tyr³²³ p38 correlates with RA disease activity and suggest that the Tyr³²³-dependent pathway is an attractive target for down-regulation of p38 activity in RA patients.

Centromere fission, not telomere erosion, triggers chromosomal instability in human carcinomas

The majority of sporadic carcinomas suffer from a kind of genetic instability in which chromosome number changes occur together with segmental defects. This means that changes involving intact chromosomes accompany breakage-induced alterations. Whereas the causes of aneuploidy are described in detail, the origins of chromosome breakage in sporadic carcinomas remain disputed. The three main pathways of chromosomal instability (CIN) proposed until now (random breakage, telomere fusion and centromere fission) are largely based on animal models and in vitro experiments, and recent studies revealed several discrepancies between animal models and human cancer. Here, we discuss how the experimental systems translate to human carcinomas and compare the theoretical breakage products to data from patient material and cancer cell lines. The majority of chromosomal defects in human carcinomas comprises pericentromeric breaks that are captured by healthy telomeres, and only a minor proportion of chromosome fusions can be attributed to telomere erosion or random breakage. Centromere fission, not telomere erosion, is therefore the most probably trigger of CIN and early carcinogenesis. Similar centromere–telomere fusions might drive a subset of congenital defects and evolutionary chromosome changes.

Are aneuploidy and chromosome breakage caused by a CINgle mechanism?

Genetic instability is a hallmark of cancer. Most tumors show complex patterns of translocations, amplifications, and deletions, which have occupied scientists for decades. A specific problem arises in carcinomas with a genetic defect termed chromosomal instability; these solid tumors undergo gains and losses of entire chromosomes, as well as segmental defects caused by chromosome breaks. To date, the apparent inconsistency between intact and broken chromosomes has precluded identification of an underlying mechanism. The recent identification of centromeric breaks alongside aneuploidy in cells with spindle defects indicates that a single mechanism could account for all genetic alterations characteristic of chromosomal instability. Since a poorly controlled spindle can cause merotelic attachments, kinetochore distortion, and subsequent chromosome breakage, spindle defects can generate the sticky ends necessary to start a breakage-fusion-bridge cycle. The characteristic breakpoint of spindle-generated damage, adjacent to the centromere, also explains the losses and gains of whole chromosome arms, which are especially prominent in low-grade tumors. The recent data indicate that spindle defects are an early event in tumor formation, and an important initiator of carcinogenesis.

Merotelic attachments and non-homologous end joining are the basis of chromosomal instability

Although the large majority of solid tumors show a combination of mitotic spindle defects and chromosomal instability, little is known about the mechanisms that govern the initial steps in tumorigenesis. The recent report of spindle-induced DNA damage provides evidence for a single mechanism responsible for the most prominent genetic defects in chromosomal instability. Spindle-induced DNA damage is brought about by uncorrected merotelic attachments, which cause kinetochore distortion, chromosome breakage at the centromere, and possible activation of DNA damage repair pathways. Although merotelic attachments are common early in mitosis, some escape detection by the kinetochore pathway. As a consequence, a proportion of merotelic attachments gives rise to chromosome breakage in normal cells and in carcinomas. An intrinsic chromosome segregation defect might thus form the basis of tumor initiation. We propose a hypothesis in which merotelic attachments and chromosome breakage establish a feedback loop that results in relaxation of the spindle checkpoint and suppression of anti-proliferative pathways, thereby promoting carcinogenesis.

Dynamic regulation of CXCR1 and CXCR2 homo- and heterodimers

Although homo- and heterodimerization are reported for some chemokine receptors, it remains unclear whether these functional states are in dynamic equilibrium and how receptor/ligand levels influence oligomerization. In human neutrophils and in cell lines that coexpress the chemokine receptors CXCR1 and CXCR2, we used fluorescence resonance energy transfer techniques to show that these two receptors form homo- and heterodimers. Receptor expression and ligand activation were found to regulate the balance between these complexes, adapting the response to changes in the milieu. CXCL8, a ligand for both receptors, alters heterodimeric complexes, whereas it stabilizes homodimers and promotes receptor internalization. Oligomerization of receptors, together with the regulation of their expression and desensitization, could thus contribute to the fine control of chemokine functions.

CCR6 regulates EAE pathogenesis by controlling regulatory CD4+ T-cell recruitment to target tissues

The T-cell subsets, characterized by their cytokine production profiles and immune regulatory functions, depend on correct in vivo location to interact with accessory or target cells for effective immune responses. Differentiation of naive CD4(+) T cells into effectors is accompanied by sequentially regulated expression of the chemokine receptors responsible for cell recruitment to specific tissues. We studied CCR6 function in EAE, a CD4(+) T-cell-mediated CNS disease characterized by mononuclear infiltration and demyelination. CCR6(-/-) mice showed an altered time course of EAE development, with delayed onset, a higher clinical score, and more persistent symptoms than in controls. An imbalanced cytokine profile and reduced Foxp3(+) cell frequency characterized CNS tissues from CCR6(-/-) compared with CCR6(+/+) mice during the disease effector phase. Transfer of CCR6(+/+) Treg to CCR6(-/-) mice the day before EAE induction reduced the clinical score associated with an increased in infiltrating Foxp3(+) cells and recovery of the cytokine balance in CCR6(-/-) mouse CNS. Competitive assays between CCR6(+/+) and CCR6(-/-) Treg adoptively transferred to CCR6(-/-) mice showed impaired ability of CCR6(-/-) Treg to infiltrate CNS tissues in EAE-affected mice. Our data indicate a CCR6 requirement by CD4(+) Treg to downregulate the CNS inflammatory process and neurological signs associated with EAE.

Synaptonemal complex assembly and H3K4Me3 demethylation determine DIDO3 localization in meiosis

Synapsis of homologous chromosomes is a key meiotic event, mediated by a large proteinaceous structure termed the synaptonemal complex. Here, we describe a role in meiosis for the murine death-inducer obliterator (Dido) gene. The Dido gene codes for three proteins that recognize trimethylated histone H3 lysine 4 through their amino-terminal plant homeodomain domain. DIDO3, the largest of the three isoforms, localizes to the central region of the synaptonemal complex in germ cells. DIDO3 follows the distribution of the central region protein SYCP1 in Sycp3-/- spermatocytes, which lack the axial elements of the synaptonemal complex. This indicates that synapsis is a requirement for DIDO3 incorporation. Interestingly, DIDO3 is missing from the synaptonemal complex in Atm mutant spermatocytes, which form synapses but show persistent trimethylation of histone H3 lysine 4. In order to further address a role of epigenetic modifications in DIDO3 localization, we made a mutant of the Dido gene that produces a truncated DIDO3 protein. This truncated protein, which lacks the histone-binding domain, is incorporated in the synaptonemal complex irrespective of histone trimethylation status. DIDO3 protein truncation in Dido mutant mice causes mild meiotic defects, visible as gaps in the synaptonemal complex, but allows for normal meiotic progression. Our results indicate that histone H3 lysine 4 demethylation modulates DIDO3 localization in meiosis and suggest epigenetic regulation of the synaptonemal complex.

Co-regulation analysis of closely linked genes identifies a highly recurrent gain on chromosome 17q25.3 in prostate cancer

Background

Transcriptional profiling of prostate cancer (PC) has unveiled new markers of neoplasia and allowed insights into mechanisms underlying this disease. Genomewide analyses have also identified new chromosomal abnormalities associated with PC. The combination of both classes of data for the same sample cohort might provide better criteria for identifying relevant factors involved in neoplasia. Here we describe transcriptional signatures identifying distinct normal and tumoral prostate tissue compartments, and the inference and demonstration of a new, highly recurrent copy number gain on chromosome 17q25.3.

Methods

We have applied transcriptional profiling to tumoral and non-tumoral prostate samples with relatively homogeneous epithelial representations as well as pure stromal tissue from peripheral prostate and cultured cell lines, followed by quantitative RT-PCR validations and immunohistochemical analysis. In addition, we have performed in silico colocalization analysis of co-regulated genes and validation by fluorescent in situ hybridization (FISH).

Results

The transcriptomic analysis has allowed us to identify signatures corresponding to non-tumoral luminal and tumoral epithelium, basal epithelial cells, and prostate stromal tissue. In addition, in silico analysis of co-regulated expression of physically linked genes has allowed us to predict the occurrence of a copy number gain at chromosomal region 17q25.3. This computational inference was validated by fluorescent in situ hybridization, which showed gains in this region in over 65% of primary and metastatic tumoral samples.

Conclusion

Our approach permits to directly link gene copy number variations with transcript co-regulation in association with neoplastic states. Therefore, transcriptomic studies of carefully selected samples can unveil new diagnostic markers and transcriptional signatures highly specific of PC, and lead to the discovery of novel genomic abnormalities that may provide additional insights into the causes and mechanisms of prostate cancer.

Statins induce regulatory T cell recruitment via a CCL1 dependent pathway

The statins, a group of inhibitors of the 3-hydroxy-3-methylglutaryl coenzyme A reductase, are reported to influence a variety of immune system activities through 3-hydroxy-3-methylglutaryl coenzyme A reductase-dependent and -independent mechanisms. How statin treatment regulates immune system function in vivo nonetheless remains to be fully defined. We analyzed the immunomodulatory effects of lovastatin in a Candida albicans-induced delayed-type hypersensitivity reaction in mice. In this model, lovastatin administration reduced the acute inflammatory response elicited by C. albicans challenge. This anti-inflammatory activity of lovastatin was associated with a shift from a Th1 to a Th2 immune response, as well as an increase in the percentage of regulatory T cells at the inflammation site and in the regional draining lymph node. The lovastatin-induced increase in regulatory T cells in the inflamed skin was dependent on expression of CCL1, a chemokine that is locally up-regulated by statin administration. The anti-inflammatory effect of lovastatin was abrogated in CCL1-deficient mice. These results suggest that local regulation of chemokine expression may be an important process in statin-induced modulation of the immune system.

Ligand stabilization of CXCR4/delta-opioid receptor heterodimers reveals a mechanism for immune response regulation

The CXCR4 chemokine receptor and the delta opioid receptor (DOR) are pertussis toxin-sensitive G protein-coupled receptors (GPCR). Both are widely distributed in brain tissues and immune cells, and have key roles in inflammation processes and in pain sensation on proximal nerve endings. We show that in immune cells expressing CXCR4 and DOR, simultaneous addition of their ligands CXCL12 and [D-Pen2, D-Pen5]enkephalin does not trigger receptor function. This treatment does not affect ligand binding or receptor expression, nor does it promote heterologous desensitization. Our data indicate that CXCR4 and DOR form heterodimeric complexes that are dynamically regulated by the ligands. This is compatible with a model in which GPCR oligomerization leads to suppression of signaling, promoting a dominant negative effect. Knockdown of CXCR4 and DOR signaling by heterodimerization might have repercussions on physiological and pathological processes such as inflammation, pain sensation and HIV-1 infection.

Type I phosphatidylinositol 4-phosphate 5-kinase controls neutrophil polarity and directional movement

Directional cell movement in response to external chemical gradients requires establishment of front–rear asymmetry, which distinguishes an up-gradient protrusive leading edge, where Rac-induced F-actin polymerization takes place, and a down-gradient retractile tail (uropod in leukocytes), where RhoA-mediated actomyosin contraction occurs. The signals that govern this spatial and functional asymmetry are not entirely understood. We show that the human type I phosphatidylinositol 4-phosphate 5-kinase isoform β (PIPKIβ) has a role in organizing signaling at the cell rear. We found that PIPKIβ polarized at the uropod of neutrophil-differentiated HL60 cells. PIPKIβ localization was independent of its lipid kinase activity, but required the 83 C-terminal amino acids, which are not homologous to other PIPKI isoforms. The PIPKIβ C terminus interacted with EBP50 (4.1-ezrin-radixin-moesin (ERM)-binding phosphoprotein 50), which enabled further interactions with ERM proteins and the Rho-GDP dissociation inhibitor (RhoGDI). Knockdown of PIPKIβ with siRNA inhibited cell polarization and impaired cell directionality during dHL60 chemotaxis, suggesting a role for PIPKIβ in these processes.

Disrupted cardiac development but normal hematopoiesis in mice deficient in the second CXCL12/SDF-1 receptor, CXCR7

Chemotactic cytokines (chemokines) attract immune cells, although their original evolutionary role may relate more closely with embryonic development. We noted differential expression of the chemokine receptor CXCR7 (RDC-1) on marginal zone B cells, a cell type associated with autoimmune diseases. We generated Cxcr7(-/-) mice but found that CXCR7 deficiency had little effect on B cell composition. However, most Cxcr7(-/-) mice died at birth with ventricular septal defects and semilunar heart valve malformation. Conditional deletion of Cxcr7 in endothelium, using Tie2-Cre transgenic mice, recapitulated this phenotype. Gene profiling of Cxcr7(-/-) heart valve leaflets revealed a defect in the expression of factors essential for valve formation, vessel protection, or endothelial cell growth and survival. We confirmed that the principal chemokine ligand for CXCR7 was CXCL12/SDF-1, which also binds CXCR4. CXCL12 did not induce signaling through CXCR7; however, CXCR7 formed functional heterodimers with CXCR4 and enhanced CXCL12-induced signaling. Our results reveal a specialized role for CXCR7 in endothelial biology and valve development and highlight the distinct developmental role of evolutionary conserved chemokine receptors such as CXCR7 and CXCR4.

Activation of the epidermal growth factor signalling pathway by tissue plasminogen activator in pancreas cancer cells

BACKGROUND

Tissue plasminogen activator (tPA) is the major activator of plasminogen in plasma. This serine protease is overexpressed by exocrine pancreas tumour cells, where it promotes tumour cell proliferation, growth, and invasion. Here we have explored the signalling pathways used by tPA to activate the proliferation of pancreatic cancer cells.

METHODS

Transcriptional profiling on cDNA micro arrays was used to analyse the pattern of gene expression in response to tPA compared to the response to epidermal growth factor (EGF) and platelet derived growth factor (PDGF). Results were confirmed using different biochemical assays in which specific kinase inhibitors or RNA interference were used.

RESULTS

Transcriptional profiling showed that tPA modulates the expression of a set of genes commonly regulated by EGF, but distinct from the major set of genes modulated by PDGF. This suggested that tPA and EGF share common signalling pathways, a conclusion supported by further experimental evidence. Firstly, we found that tPA induced a rapid and transient phosphorylation of the EGFR. Secondly, specific EGFR kinase inhibitors, but not PDGFR kinase inhibitors, abolished the tPA induced phosphorylation of the ERK1/2 kinases and cell proliferation. The mitogenic activity of tPA was also inhibited by siRNA depletion of EGFR, thus confirming the involvement of this receptor in tPA triggered signalling. Thirdly, we show that the signalling and mitogenic effects of tPA require its proteolytic activity, the activity of the metalloprotease-9 and active hb-EGF.

CONCLUSION

Our results suggest that tPA induces proliferation by triggering a proteolytic cascade that sequentially activates plasmin, metalloprotease-9 (MMP-9) and hb-EGF. These events are required to activate the EGFR signalling pathway and cell proliferation.

c-Myc is essential for hematopoietic stem cell differentiation and regulates Lin(-)Sca-1(+)c-Kit(-) cell generation through p21

OBJECTIVE

The c-Myc protein is a member of the basic region/helix-loop-helix/leucine zipper (bHLHZip) transcription factor family, which is implicated in regulation of proliferation, differentiation, and apoptosis in multiple cell types. The aim of this study was to characterize the role of the proto-oncogene c-myc in hematopoietic stem cells (HSC) during postnatal development.

MATERIAL AND METHODS

We have generated a conditional mouse model that allows us to inactivate c-myc in bone marrow (BM) in an inducible fashion.

RESULTS

We show that conditional inactivation of c-Myc in BM severely impairs HSC differentiation, leading to a striking decrease in the number of lymphoid and myeloid cells. c-Myc deletion in BM causes substantial accumulation of a Lin(-)Sca-1(+)c-Kit(-) cell population expressing high levels of the cell-cycle inhibitor p21, whose origin and function are otherwise poorly characterized. In vivo inactivation of p21 and c-Myc normalizes Lin(-)Sca-1(+)c-Kit(-) cell numbers and restores normal proliferation. The potential origin and function of these cells are discussed.

CONCLUSIONS

c-Myc plays a role in HSC maintenance and differentiation and might be regulating generation of Lin(-)Sca-1(+)c-Kit(-) through the cell-cycle regulator p21.

Filamin-A regulates actin-dependent clustering of HIV receptors

Human immunodeficiency virus (HIV)-1 infection requires envelope (Env) glycoprotein gp120-induced clustering of CD4 and coreceptors (CCR5 or CXCR4) on the cell surface; this enables Env gp41 activation and formation of a complex that mediates fusion between Env-containing and target-cell membranes. Kinetic studies show that viral receptors are actively transported to the Env-receptor interface in a process that depends on plasma membrane composition and the actin cytoskeleton. The mechanisms by which HIV-1 induces F-actin rearrangement in the target cell remain largely unknown. Here, we show that CD4 and the coreceptors interact with the actin-binding protein filamin-A, whose binding to HIV-1 receptors regulates their clustering on the cell surface. We found that gp120 binding to cell receptors induces transient cofilin-phosphorylation inactivation through a RhoA-ROCK-dependent mechanism. Blockade of filamin-A interaction with CD4 and/or coreceptors inhibits gp120-induced RhoA activation and cofilin inactivation. Our results thus identify filamin-A as an adaptor protein that links HIV-1 receptors to the actin cytoskeleton remodelling machinery, which may facilitate virus infection.

A central role for DOCK2 during interstitial lymphocyte motility and sphingosine-1-phosphate-mediated egress

Recent observations using multiphoton intravital microscopy (MP-IVM) have uncovered an unexpectedly high lymphocyte motility within peripheral lymph nodes (PLNs). Lymphocyte-expressed intracellular signaling molecules governing interstitial movement remain largely unknown. Here, we used MP-IVM of murine PLNs to examine interstitial motility of lymphocytes lacking the Rac guanine exchange factor DOCK2 and phosphoinositide-3-kinase (PI3K)γ, signaling molecules that act downstream of G protein–coupled receptors, including chemokine receptors (CKRs). T and B cells lacking DOCK2 alone or DOCK2 and PI3Kγ displayed markedly reduced motility inside T cell area and B cell follicle, respectively. Lack of PI3Kγ alone had no effect on migration velocity but resulted in increased turning angles of T cells. As lymphocyte egress from PLNs requires the sphingosine-1-phosphate (S1P) receptor 1, a G_αi protein–coupled receptor similar to CKR, we further analyzed whether DOCK2 and PI3Kγ contributed to S1P-triggered signaling events. S1P-induced cell migration was significantly reduced in T and B cells lacking DOCK2, whereas T cell–expressed PI3Kγ contributed to F-actin polymerization and protein kinase B phosphorylation but not migration. These findings correlated with delayed lymphocyte egress from PLNs in the absence of DOCK2 but not PI3Kγ, and a markedly reduced cell motility of DOCK2-deficient T cells in close proximity to efferent lymphatic vessels. In summary, our data support a central role for DOCK2, and to a lesser extent T cell–expressed PI3Kγ, for signal transduction during interstitial lymphocyte migration and S1P-mediated egress.

Sequential loading of cohesin subunits during the first meiotic prophase of grasshoppers

The cohesin complexes play a key role in chromosome segregation during both mitosis and meiosis. They establish sister chromatid cohesion between duplicating DNA molecules during S-phase, but they also have an important role during postreplicative double-strand break repair in mitosis, as well as during recombination between homologous chromosomes in meiosis. An additional function in meiosis is related to the sister kinetochore cohesion, so they can be pulled by microtubules to the same pole at anaphase I. Data about the dynamics of cohesin subunits during meiosis are scarce; therefore, it is of great interest to characterize how the formation of the cohesin complexes is achieved in order to understand the roles of the different subunits within them. We have investigated the spatio-temporal distribution of three different cohesin subunits in prophase I grasshopper spermatocytes. We found that structural maintenance of chromosome protein 3 (SMC3) appears as early as preleptotene, and its localization resembles the location of the unsynapsed axial elements, whereas radiation-sensitive mutant 21 (RAD21) (sister chromatid cohesion protein 1, SCC1) and stromal antigen protein 1 (SA1) (sister chromatid cohesion protein 3, SCC3) are not visualized until zygotene, since they are located in the synapsed regions of the bivalents. During pachytene, the distribution of the three cohesin subunits is very similar and all appear along the trajectories of the lateral elements of the autosomal synaptonemal complexes. However, whereas SMC3 also appears over the single and unsynapsed X chromosome, RAD21 and SA1 do not. We conclude that the loading of SMC3 and the non-SMC subunits, RAD21 and SA1, occurs in different steps throughout prophase I grasshopper meiosis. These results strongly suggest the participation of SMC3 in the initial cohesin axis formation as early as preleptotene, thus contributing to sister chromatid cohesion, with a later association of both RAD21 and SA1 subunits at zygotene to reinforce and stabilize the bivalent structure. Therefore, we speculate that more than one cohesin complex participates in the sister chromatid cohesion at prophase I.

Dido disruption leads to centrosome amplification and mitotic checkpoint defects compromising chromosome stability

Numerical and/or structural centrosome abnormalities have been correlated with most solid tumors and hematological malignancies. Tumorigenesis also is linked to defects in the mitotic or spindle assembly checkpoint, a key control mechanism that ensures accurate segregation of chromosomes during mitosis. We have reported that targeted disruption of the Dido gene causes a transplantable myelodysplastic/myeloproliferative disease in mice. Here, we report that Dido3, the largest splice variant of the Dido gene, is a centrosome-associated protein whose disruption leads to supernumerary centrosomes, failure to maintain cellular mitotic arrest, and early degradation of the mitotic checkpoint protein BubR1. These aberrations result in enhanced aneuploidy in the Dido mutant cells. Dido gene malfunction thus is reported to be part of an impaired signaling cascade that results in a defective mitotic checkpoint, leading to chromosome instability.

p21CIP1/WAF1 Controls Proliferation of Activated/Memory T Cells and Affects Homeostasis and Memory T Cell Responses

Development of autoantibodies and lupus-like autoimmunity by 129/Sv x C57BL/6 p21(-/-) mice has established that cell cycle deregulation is one the defective pathways leading to break of tolerance. Memory T cell accumulation is thought to be related to tolerance loss in murine lupus models. We studied T cell memory responses in C57BL/6 p21(-/-) mice that develop lupus-like disease manifestations. p21 did not affect primary proliferation of naive T cells, and was required for cycling control, but not for apoptosis of activated/memory T cells. When we induced apoptosis by secondary TCR challenge, surviving memory T cells depended on p21 for proliferation control. Under conditions of secondary T cell stimulation that did not cause apoptosis, p21 was also needed for regulation of activated/memory T cell expansion. The requirement for p21 in the control of T cell proliferation of activated/memory T cells suggests that in addition to apoptosis, cycling regulation by p21 constitutes a new pathway for T cell homeostasis. Concurring with this view, we found accumulation in p21(-/-) mice of memory CD4(+) T cells that showed increased proliferative potential after TCR stimulation. Furthermore, OVA immunization of p21(-/-) mice generated hyperresponsive OVA-specific T cells. Overall, the data show that p21 controls the proliferation of only activated/memory T cells, and suggest that p21 forms part of the memory T cell homeostasis mechanism, contributing to maintenance of tolerance.

CCR6 regulates the function of alloreactive and regulatory CD4+ T cells during acute graft-versus-host disease

The chemokine receptor CCR6 is expressed by CD4+ T cell effector/memory and regulatory effector/memory (TREM) subsets. Here we show that CCR6 modulates graft-versus-host-disease (GVHD) responses in both alloreactive CD4+ T effector cells and regulatory T (Treg) cells. Mortality and morbidity due to acute GVHD were drastically reduced and delayed when naïve T cells were derived from CCR6-deficient donor mice. This deficiency also affected the suppressive ability of Treg cells in GVHD. CCR6-/- Treg cells were able to suppress T cell proliferation in vitro, but their in vivo capacity to downregulate target tissue damage induced by naïve wild type (WT) T cells was impaired. The data demonstrate a requirement for CCR6 in CD4+ T cell function in GVHD, in both effector and regulatory cell subsets.

Chemokine signaling defines novel targets for therapeutic intervention

Members of the human chemokine family are considered a suitable target for therapeutic intervention, as they have a fundamental role in several important human diseases. Here we outline potential new areas of intervention based on recent findings on chemokine receptor function.

Inducible model for beta-six-mediated site-specific recombination in mammalian cells

The prokaryotic β recombinase catalyzes site-specific recombination between two directly oriented minimal six sites in chromatin-integrated substrates. Here, we demonstrate that an enhanced green fluorescent protein (EGFP)-fused version of β recombinase (β-EGFP) is fully active, retaining most specific activity. It is used to develop a recombination-dependent activatable gene expression (RAGE) system based on the androgen receptor (AR) ligand-binding domain (LBD). Two hybrid molecules, a direct fusion of the LBD-AR to the C-terminus of β recombinase (β-AR) and a triple fusion of β-EGFP to the same ligand-binding domain (β-EGFP-AR), were engineered and their subcellular behavior, stability and catalytic activity were evaluated. Both chimeric β recombinase proteins showed in vivo inducible recombinogenic activity dependent on addition of an androgen receptor agonist, although the β-AR fusion protein demonstrated more accurate ligand-dependent translocation from cytoplasm to nucleus.