c-Myb regulates lineage choice in developing thymocytes via its target gene Gata3

The CD4 Versus CD8 T Cell Fate Decision: A Multiomics-Informed Perspective

The choice of developing thymocytes to become CD8+ cytotoxic or CD4+ helper T cells has been intensely studied, but many of the underlying mechanisms remain to be elucidated. Recent multiomics approaches have provided much higher resolution analysis of gene expression in developing thymocytes than was previously achievable, thereby offering a fresh perspective on this question. Focusing on our recent studies using CITE-seq (cellular indexing of transcriptomes and epitopes) analyses of mouse thymocytes, we present a detailed timeline of RNA and protein expression changes during CD8 versus CD4 T cell differentiation. We also revisit our current understanding of the links between T cell receptor signaling and expression of the lineage-defining transcription factors ThPOK and RUNX3. Finally, we propose a sequential selection model to explain the tight linkage between MHC-I versus MHC-II recognition and T cell lineage choice. This model incorporates key aspects of previously proposed kinetic signaling, instructive, and stochastic/selection models.

Molecular dynamics simulation reveals DNA-specific recognition mechanism via c-Myb in pseudo-palindromic consensus of mim-1 promoter

This study aims to gain insight into the DNA-specific recognition mechanism of c-Myb transcription factor during the regulation of cell early differentiation and proliferation. Therefore, we chose the chicken myeloid gene, mitochondrial import protein 1 (mim-1), as a target to study the binding specificity between potential dual-Myb-binding sites. The c-Myb-binding site in mim-1 is a pseudo-palindromic sequence AACGGTT, which contains two AACNG consensuses. Simulation studies in different biological scenarios revealed that c-Myb binding with mim-1 in the forward strand (complex F) ismore stable than that inthereverse strand (complex R). The principal component analysis (PCA) dynamics trajectory analyses suggested an opening motion of the recognition helices of R2 and R3 (R2R3), resulting in the dissociation of DNA from c-Myb in complex R at 330 K, triggered by the reduced electrostatic potential on the surface of R2R3. Furthermore, the DNA confirmation and hydrogen-bond interaction analyses indicated that the major groove width of DNA increased in complex R, which affected on the hydrogen-bond formation ability between R2R3 and DNA, and directly resulted in the dissociation of DNA from R2R3. The steered molecular dynamics (SMD) simulation studies also suggested that the electrostatic potential, major groove width, and hydrogen bonds made major contribution to the DNA‍-specific recognition. In vitro trials confirmed the simulation results that c-Myb specifically bound to mim-1 in the forward strand. This study indicates that the three-dimensional (3D) structure features play an important role in the DNA-specific recognition mechanism by c-Myb besides the AACNG consensuses, which is beneficial to understanding the cell early differentiation and proliferation regulated by c-Myb, as well as the prediction of novel c-Myb-binding motifs in tumorigenesis.

The Promise of Single-cell Technology in Providing New Insights Into the Molecular Heterogeneity and Management of Acute Lymphoblastic Leukemia

Drug resistance and treatment failure in pediatric acute lymphoblastic leukemia (ALL) are in part driven by tumor heterogeneity and clonal evolution. Although bulk tumor genomic analyses have provided some insight into these processes, single-cell sequencing has emerged as a powerful technique to profile individual cells in unprecedented detail. Since the introduction of single-cell RNA sequencing, we now have the capability to capture not only transcriptomic, but also genomic, epigenetic, and proteomic variation between single cells separately and in combination. This rapidly evolving field has the potential to transform our understanding of the fundamental biology of pediatric ALL and guide the management of ALL patients to improve their clinical outcome. Here, we discuss the impact single-cell sequencing has had on our understanding of tumor heterogeneity and clonal evolution in ALL and provide examples of how single-cell technology can be integrated into the clinic to inform treatment decisions for children with high-risk disease.

SRSF1 Deficiency Impairs the Late Thymocyte Maturation and the CD8 Single-Positive Lineage Fate Decision

The underlying mechanisms of thymocyte development and lineage determination remain incompletely understood, and the emerging evidences demonstrated that RNA binding proteins (RBPs) are deeply involved in governing T cell fate in thymus. Serine/arginine-rich splicing factor 1 (SRSF1), as a classical splicing factor, is a pivotal RBP for gene expression in various biological processes. Our recent study demonstrated that SRSF1 plays essential roles in the development of late thymocytes by modulating the T cell regulatory gene networks post-transcriptionally, which are critical in response to type I interferon signaling for supporting thymocyte maturation. Here, we report SRSF1 also contributes to the determination of the CD8⁺ T cell fate. By specific ablation of SRSF1 in CD4⁺CD8⁺ double positive (DP) thymocytes, we found that SRSF1 deficiency impaired the maturation of late thymocytes and diminished the output of both CD4⁺ and CD8⁺ single positive T cells. Interestingly, the ratio of mature CD4⁺ to CD8⁺ cells was notably altered and more severe defects were exhibited in CD8⁺ lineage than those in CD4⁺ lineage, reflecting the specific function of SRSF1 in CD8⁺ T cell fate decision. Mechanistically, SRSF1-deficient cells downregulate their expression of Runx3, which is a crucial transcriptional regulator in sustaining CD8⁺ single positive (SP) thymocyte development and lineage choice. Moreover, forced expression of Runx3 partially rectified the defects in SRSF1-deficient CD8⁺ thymocyte maturation. Thus, our data uncovered the previous unknown role of SRSF1 in establishment of CD8⁺ cell identity.

-Omic Analysis of the Sepia officinalis White Body: New Insights into Multifunctionality and Haematopoiesis Regulation

Cephalopods, like other protostomes, lack an adaptive immune system and only rely on an innate immune system. The main immune cells are haemocytes (Hcts), which are able to respond to pathogens and external attacks. First reports based on morphological observations revealed that the white body (WB) located in the optic sinuses of cuttlefish was the origin of Hcts. Combining transcriptomic and proteomic analyses, we identified several factors known to be involved in haematopoiesis in vertebrate species in cuttlefish WB. Among these factors, members of the JAK-STAT signaling pathway were identified, some of them for the first time in a molluscan transcriptome and proteome. Immune factors, such as members of the Toll/NF-κB signaling pathway, pattern recognition proteins and receptors, and members of the oxidative stress responses, were also identified, and support an immune role of the WB. Both transcriptome and proteome analyses revealed that the WB harbors an intense metabolism concurrent with the haematopoietic function. Finally, a comparative analysis of the WB and Hct proteomes revealed many proteins in common, confirming previous morphological studies on the origin of Hcts in cuttlefish. This molecular work demonstrates that the WB is multifunctional and provides bases for haematopoiesis regulation in cuttlefish.

Dynamic regulation of chromatin organizer SATB1 via TCR-induced alternative promoter switch during T-cell development

The chromatin organizer SATB1 is highly enriched in thymocytes and is essential for T-cell development. Although SATB1 regulates a large number of genes important for T-cell development, the mechanism(s) regulating expression of SATB1 during this process remain elusive. Using chromatin immune precipitation-seq-based occupancy profiles of H3K4me3 and H3Kme1 at Satb1 gene locus, we predicted four different alternative promoters of Satb1 in mouse thymocytes and characterized them. The expression of Satb1 transcript variants with distinct 5′ UTRs occurs in a stage-specific manner during T-cell development and is dependent on TCR signaling. The observed discrepancy between the expression levels of SATB1 mRNA and protein in developing thymocytes can be explained by the differential translatability of Satb1 transcript variants as confirmed by polysome profiling and in vitro translation assay. We show that Satb1 alternative promoters exhibit lineage-specific chromatin accessibility during T-cell development from progenitors. Furthermore, TCF1 regulates the Satb1 P2 promoter switch during CD4SP development, via direct binding to the Satb1 P2 promoter. CD4SP T cells from TCF1 KO mice exhibit downregulation of P2 transcript variant expression as well as low levels of SATB1 protein. Collectively, these results provide unequivocal evidence toward alternative promoter switch-mediated developmental stage-specific regulation of SATB1 in thymocytes.

Dynamic control of the T-cell specification gene regulatory network

Specification of multipotent blood precursor cells in postnatal mice to become committed T-cell precursors involves a gene regulatory network of several interacting but functionally distinct modules. Many links of this network have been defined by perturbation tests and by functional genomics. However, using the network model to predict real-life kinetics of the commitment process is still difficult, partly due to the tenacity of repressive chromatin states, and to the ability of transcription factors to affect each other's binding site choices through competitive recruitment to alternative sites ("coregulator theft"). To predict kinetics, future models will need to incorporate mechanistic information about chromatin state change dynamics and more sophisticated understanding of the proteomics and cooperative DNA site choices of transcription factor complexes.

Transcriptional Regulation of Differentiation and Functions of Effector T Regulatory Cells

Foxp3-expressing regulatory T (Treg) cells can suppress the activity of various types of immune cells and play key roles in the maintenance of self-tolerance and in the regulation of immune responses against pathogens and tumor cells. Treg cells consist of heterogeneous subsets that have distinct phenotypes and functions. Upon antigen stimulation, naïve-like thymus-derived Treg cells, which circulate in secondary lymphoid organs, can differentiate into effector Treg (eTreg) cells and migrate to and control immune homeostasis of peripheral tissues. eTreg cells are heterogeneous in terms of their ability to localize to specific tissues and suppress particular types of immune responses. Differentiation and function of diverse eTreg subsets are regulated by a variety of transcription factors that are activated by antigens and cytokines. In this article, we review the current understanding of the transcriptional regulation of differentiation and function of eTreg cells.

Critical Role for TCR Signal Strength and MHC Specificity in ThPOK-Induced CD4 Helper Lineage Choice

Sustained TCR signaling is critical for ThPOK induction in MHC class II (MHCII)-signaled thymocytes leading to the CD4 helper lineage commitment. ThPOK suppresses the cytotoxic program in the signaled thymocytes and is shown to be necessary and sufficient for the CD4 helper lineage choice. Accordingly, loss and gain of ThPOK function redirects MHCII- and MHC class I (MHCI)-signaled thymocytes into the CD8 cytotoxic and CD4 helper lineage, respectively. However, the impact of a defined ThPOK level on the CD4 helper lineage choice of MHCII- and MHCI-specific thymocytes and the role of TCR signaling in this process is not evaluated. Equally, it is not clear if suppression of the cytotoxic program by ThPOK is sufficient in redirecting MHCI-restricted thymocytes into the CD4 helper lineage. In this study, we have investigated CD8 to CD4 helper lineage redirection in three independent ThPOK overexpressing transgenic mouse lines. Our analysis shows that one of the transgenic lines, despite overexpressing ThPOK compared with wild-type CD4 mature T cells and compromising cytotoxic program, failed to redirect all MHCI-signaled thymocytes into the CD4 helper lineage, resulting in the continued presence of CD8⁺ mature T cells and the generation of a large number of double negative mature T cells. Critically, the same ThPOK transgene completely restored the CD4 helper lineage commitment of MHCII-specific Thpok ^-/- thymocytes. Importantly, augmenting TCR signaling significantly enhanced the ThPOK-mediated CD4 helper lineage choice of MHCI-specific thymocytes but was still substantially less efficient than that of MHCII-specific thymocytes expressing the same amount of ThPOK. Together, these data suggest that the ThPOK-induced CD4 helper lineage commitment is strongly influenced by TCR signal strength and MHC specificity of developing thymocytes.

MYB - A regulatory factor in hematopoiesis

MYB is a transcription factor which was identified in birds as a viral oncogene (v-MYB). Its cellular counterpart was subsequently isolated as c-MYB which has three functional domains - DNA binding domain, transactivation domain and negative regulatory domain. c-MYB is essential for survival, and deletion of both alleles of the gene results in embryonic death. It is highly expressed in hematopoietic cells, thymus and neural tissue, and required for T and B lymphocyte development and erythroid maturation. Additionally, aberrant MYB expression has been found in numerous solid cancer cells and human leukemia. Recent studies have also implicated c-MYB in the regulation of expression of fetal hemoglobin which is highly beneficial to the β-hemoglobinopathies (beta thalassemia and sickle cell disease). These findings suggest that MYB could be a potential therapeutic target in leukemia, and possibly also a target for therapeutic increase of fetal hemoglobin in the β-hemoglobinopathies.

Transfer of multiple loci of donor's genes to induce recipient tolerance in organ transplantation

Donor organ rejection remains a significant problem. The present study aimed to assess whether transferring a donor's major histocompatibility complex (MHC) genes to the recipient could mitigate rejection in organ transplantation. Seven loci of MHC genes from donor mice were amplified and ligated into vectors; the vectors either contained one K locus, seven loci or were empty (control). The vectors were subsequently injected into the thymus of recipients (in heterotransplants, recipient rats received the vector containing one K locus), following which donor mouse hearts were transplanted. Following the transplantation of allograft and heterograft, electrocardiosignals were viable for a significantly longer duration in recipient mice and rats receiving the donor histocompatibility-2 complex (H-2)^d genes compared with those in controls, and in mice that received seven vectors compared with those receiving one vector. Mixed lymphocyte cultures containing cells from these recipients proliferated significantly less compared with mixed lymphocyte cultures containing controls. Also, hearts from H-2^d genes-treated recipients demonstrated less lymphocyte infiltration and necrosis compared with the control recipient. The present study concluded that allograft and heterograft rejection may be mitigated by introducing the donor's MHC into the recipient; transferring seven loci has been demonstrated to be more effective than transferring one locus.

A Decade of GWAS Results in Lung Cancer

Genome-wide association studies (GWAS) were successful to identify genetic factors robustly associated with lung cancer. This review aims to synthesize the literature in this field and accelerate the translation of GWAS discoveries into results that are closer to clinical applications. A chronologic presentation of published GWAS on lung cancer susceptibility, survival, and response to treatment is presented. The most important results are tabulated to provide a concise overview in one read. GWAS have reported 45 lung cancer susceptibility loci with varying strength of evidence and highlighted suspected causal genes at each locus. Some genetic risk loci have been refined to more homogeneous subgroups of lung cancer patients in terms of histologic subtypes, smoking status, gender, and ethnicity. Overall, these discoveries are an important step for future development of new therapeutic targets and biomarkers to personalize and improve the quality of care for patients. GWAS results are on the edge of offering new tools for targeted screening in high-risk individuals, but more research is needed if GWAS are to pay off the investment. Complementary genomic datasets and functional studies are needed to refine the underlying molecular mechanisms of lung cancer preliminarily revealed by GWAS and reach results that are medically actionable. Cancer Epidemiol Biomarkers Prev; 27(4); 363-79. ©2018 AACRSee all articles in this CEBP Focus section, "Genome-Wide Association Studies in Cancer."

Th-POK regulates mammary gland lactation through mTOR-SREBP pathway

The Th-inducing POK (Th-POK, also known as ZBTB7B or cKrox) transcription factor is a key regulator of lineage commitment of immature T cell precursors. It is yet unclear the physiological functions of Th-POK besides helper T cell differentiation. Here we show that Th-POK is restrictedly expressed in the luminal epithelial cells in the mammary glands that is upregulated at late pregnancy and lactation. Lineage restrictedly expressed Th-POK exerts distinct biological functions in the mammary epithelial cells and T cells in a tissue-specific manner. Th-POK is not required for mammary epithelial cell fate determination. Mammary gland morphogenesis in puberty and alveologenesis in pregnancy are phenotypically normal in the Th-POK-deficient mice. However, Th-POK-deficient mice are defective in triggering the onset of lactation upon parturition with large cellular lipid droplets retained within alveolar epithelial cells. As a result, Th-POK knockout mice are unable to efficiently secret milk lipid and to nurse the offspring. Such defect is mainly attributed to the malfunctioned mammary epithelial cells, but not the tissue microenvironment in the Th-POK deficient mice. Th-POK directly regulates expression of insulin receptor substrate-1 (IRS-1) and insulin-induced Akt-mTOR-SREBP signaling. Th-POK deficiency compromises IRS-1 expression and Akt-mTOR-SREBP signaling in the lactating mammary glands. Conversely, insulin induces Th-POK expression. Thus, Th-POK functions as an important feed-forward regulator of insulin signaling in mammary gland lactation.

Transcription factor c-Myb inhibits breast cancer lung metastasis by suppression of tumor cell seeding

Metastasis accounts for most of cancer-related deaths. Paracrine signaling between tumor cells and the stroma induces changes in the tumor microenvironment required for metastasis. Transcription factor c-Myb was associated with breast cancer (BC) progression but its role in metastasis remains unclear. Here we show that increased c-Myb expression in BC cells inhibits spontaneous lung metastasis through impaired tumor cell extravasation. On contrary, BC cells with increased lung metastatic capacity exhibited low c-Myb levels. We identified a specific inflammatory signature, including Ccl2 chemokine, that was expressed in lung metastatic cells but was suppressed in tumor cells with higher c-Myb levels. Tumor cell-derived Ccl2 expression facilitated lung metastasis and rescued trans-endothelial migration of c-Myb overexpressing cells. Clinical data show that the identified inflammatory signature, together with a MYB expression, predicts lung metastasis relapse in BC patients. These results demonstrate that the c-Myb-regulated transcriptional program in BCs results in a blunted inflammatory response and consequently suppresses lung metastasis.

Effector Regulatory T Cell Differentiation and Immune Homeostasis Depend on the Transcription Factor Myb

FoxP3-expressing regulatory T (Treg) cells are essential for maintaining immune homeostasis. Activated Treg cells undergo further differentiation into an effector state that highly expresses genes critical for Treg cell function, although how this process is coordinated on a transcriptional level is poorly understood. Here, we demonstrate that mice lacking the transcription factor Myb in Treg cells succumbed to a multi-organ inflammatory disease. Myb was specifically expressed in, and required for the differentiation of, thymus-derived effector Treg cells. The combination of transcriptome and genomic footprint analyses revealed that Myb directly regulated a large proportion of the gene expression specific to effector Treg cells, identifying Myb as a critical component of the gene regulatory network controlling effector Treg cell differentiation and function.

GATA3 and MYB Expression in Cutaneous Adnexal Neoplasms

Knowledge of staining pattern of certain immunostains might be useful in the classification of cutaneous adnexal tumors that can have clinical importance. We studied GATA3 and MYB expression in archival materials of 220 adnexal tumors comprised of sebaceous carcinomas, follicular tumors, apocrine carcinoma, predominantly apocrine tumors, predominantly eccrine tumors, and others including adenoid cystic carcinomas. Nuclear GATA3 expression was seen in 70% (153/220) of cases, including sebaceous carcinoma (93%), apocrine carcinoma (93%), follicular neoplasms (100%), and predominantly apocrine neoplasms (69%), yet only 38% of predominantly eccrine neoplasms. Nuclear MYB expression was seen in 43% (81/188) of cases, including adenoid cystic carcinoma (90%), predominantly apocrine tumors (66%), follicular neoplasms (49%), apocrine carcinomas (14%), predominantly eccrine tumors (11%), and sebaceous carcinomas (4%). GATA3 and MYB expression were noted in 43% (9/21) and 24% (5/21) of cutaneous metastases, respectively. Expression of both GATA3 and MYB was noted in 33% (60/184) of primary adnexal tumors versus 19% (4/21) of cutaneous metastases. GATA3 preferentially labels tumors with follicular, sebaceous, and apocrine differentiation. MYB is potentially a helpful stain in the distinction of desmoplastic trichoepithelioma versus basal cell carcinoma. The coexpression of GATA3 and MYB might be helpful in the distinction of primary cutaneous adnexal carcinoma versus metastatic breast, salivary gland, or urothelial carcinoma.

A rare subset of skin-tropic regulatory T cells expressing Il10/Gzmb inhibits the cutaneous immune response

Foxp3⁺ regulatory T cells (Tregs) migrating from the skin to the draining lymph node (dLN) have a strong immunosuppressive effect on the cutaneous immune response. However, the subpopulations responsible for their inhibitory function remain unclear. We investigated single-cell gene expression heterogeneity in Tregs from the dLN of inflamed skin in a contact hypersensitivity model. The immunosuppressive genes Ctla4 and Tgfb1 were expressed in the majority of Tregs. Although Il10-expressing Tregs were rare, unexpectedly, the majority of Il10-expressing Tregs co-expressed Gzmb and displayed Th1-skewing. Single-cell profiling revealed that CD43⁺ CCR5⁺ Tregs represented the main subset within the Il10/Gzmb-expressing cell population in the dLN. Moreover, CD43⁺ CCR5⁺ CXCR3⁻ Tregs expressed skin-tropic chemokine receptors, were preferentially retained in inflamed skin and downregulated the cutaneous immune response. The identification of a rare Treg subset co-expressing multiple immunosuppressive molecules and having tissue-remaining capacity offers a novel strategy for the control of skin inflammatory responses.

Dysregulation of c-Myb Pathway by Aberrant Expression of Proto-oncogene MYB Provides the Basis for Malignancy in Adult T-cell Leukemia/lymphoma Cells

PURPOSE

Adult T-cell leukemia/lymphoma (ATLL) is an aggressive human T-cell malignancy induced by human T-lymphotrophic virus-1 (HTLV-1) infection. The genetic alterations in infected cells that lead to transformation have not been completely elucidated, thus hindering the identification of effective therapeutic targets for ATL. Here, we present the first assessment of MYB proto-oncogene dysregulation in ATL and an exploration of its role in the onset of ATL.

EXPERIMENTAL DESIGN

We investigated the expression patterns of MYB splicing variants in ATL. The molecular characteristics of the c-Myb-9A isoform, which was overexpressed in ATL cells, were examined using chromatin immunoprecipitation and promoter assays. We further examined the biologic impacts of abnormal c-Myb overexpression in ATL using overall c-Myb knockdown with shRNA or c-Myb-9A knockdown with morpholino oligomers.

RESULTS

Both total c-Myb and c-Myb-9A, which exhibited strong transforming activity, were overexpressed in ATL cells in a leukemogenesis- and progression-dependent manner. Knockdown of either total c-Myb or c-Myb-9A induced ATL cell death. c-Myb transactivates nine genes that encode essential regulators of cell proliferation and NF-κB signaling. c-Myb-9A induced significantly stronger transactivation of all tested genes and stronger NF-κB activation compared with wild-type c-Myb.

CONCLUSIONS

Our data demonstrate that c-Myb pathway overactivation caused by unbalanced c-Myb-9A overexpression is associated with disorders in cellular homeostasis and consequently, accelerated transformation, cell proliferation, and malignancy in ATL cells. These data support the notion of the c-Myb pathway as a promising new therapeutic target for ATL. Clin Cancer Res; 22(23); 5915-28. ©2016 AACR.

Lineage-affiliated transcription factors bind the Gata3 Tce1 enhancer to mediate lineage-specific programs

The transcription factor GATA3 is essential for the genesis and maturation of the T cell lineage, and GATA3 dysregulation has pathological consequences. Previous studies have shown that GATA3 function in T cell development is regulated by multiple signaling pathways and that the Notch nuclear effector, RBP-J, binds specifically to the Gata3 promoter. We previously identified a T cell-specific Gata3 enhancer (Tce1) lying 280 kb downstream from the structural gene and demonstrated in transgenic mice that Tce1 promoted T lymphocyte-specific transcription of reporter genes throughout T cell development; however, it was not clear if Tce1 is required for Gata3 transcription in vivo. Here, we determined that the canonical Gata3 promoter is insufficient for Gata3 transcriptional activation in T cells in vivo, precluding the possibility that promoter binding by a host of previously implicated transcription factors alone is responsible for Gata3 expression in T cells. Instead, we demonstrated that multiple lineage-affiliated transcription factors bind to Tce1 and that this enhancer confers T lymphocyte-specific Gata3 activation in vivo, as targeted deletion of Tce1 in a mouse model abrogated critical functions of this T cell-regulatory element. Together, our data show that Tce1 is both necessary and sufficient for critical aspects of Gata3 T cell-specific transcriptional activity.

Forging T-Lymphocyte Identity: Intersecting Networks of Transcriptional Control

T-lymphocyte development branches off from other lymphoid developmental programs through its requirement for sustained environmental signals through the Notch pathway. In the thymus, Notch signaling induces a succession of T-lineage regulatory factors that collectively create the T-cell identity through distinct steps. This process involves both the staged activation of T-cell identity genes and the staged repression of progenitor-cell-inherited regulatory genes once their roles in self-renewal and population expansion are no longer needed. With the recent characterization of innate lymphoid cells (ILCs) that share transcriptional regulation programs extensively with T-cell subsets, T-cell identity can increasingly be seen as defined in modular terms, as the processes selecting and actuating effector function are potentially detachable from the processes generating and selecting clonally unique T-cell receptor structures. The developmental pathways of different classes of T cells and ILCs are distinguished by the numbers of prerequisites of gene rearrangement, selection, and antigen contact before the cells gain access to nearly common regulatory mechanisms for choosing effector function. Here, the major classes of transcription factors that interact with Notch signals during T-lineage specification are discussed in terms of their roles in these programs, the evidence for their spectra of target genes at different stages, and their cross-regulatory and cooperative actions with each other. Specific topics include Notch modulation of PU.1 and GATA-3, PU.1-Notch competition, the relationship between PU.1 and GATA-3, and the roles of E proteins, Bcl11b, and GATA-3 in guiding acquisition of T-cell identity while avoiding redirection to an ILC fate.

c-Myb Binding Sites in Haematopoietic Chromatin Landscapes

Strict control of tissue-specific gene expression plays a pivotal role during lineage commitment. The transcription factor c-Myb has an essential role in adult haematopoiesis and functions as an oncogene when rearranged in human cancers. Here we have exploited digital genomic footprinting analysis to obtain a global picture of c-Myb occupancy in the genome of six different haematopoietic cell-types. We have biologically validated several c-Myb footprints using c-Myb knockdown data, reporter assays and DamID analysis. We show that our predicted conserved c-Myb footprints are highly dependent on the haematopoietic cell type, but that there is a group of gene targets common to all cell-types analysed. Furthermore, we find that c-Myb footprints co-localise with active histone mark H3K4me3 and are significantly enriched at exons. We analysed co-localisation of c-Myb footprints with 104 chromatin regulatory factors in K562 cells, and identified nine proteins that are enriched together with c-Myb footprints on genes positively regulated by c-Myb and one protein enriched on negatively regulated genes. Our data suggest that c-Myb is a transcription factor with multifaceted target regulation depending on cell type.

TCF-1 and LEF-1 act upstream of Th-POK to promote the CD4(+) T cell fate and interact with Runx3 to silence Cd4 in CD8(+) T cells

The transcription factors TCF-1 and LEF-1 are essential for early T cell development, but their roles beyond the CD4(+)CD8(+) double-positive (DP) stage are unknown. By specific ablation of these factors in DP thymocytes, we demonstrated that deficiency in TCF-1 and LEF-1 diminished the output of CD4(+) T cells and redirected CD4(+) T cells to a CD8(+) T cell fate. The role of TCF-1 and LEF-1 in the CD4-versus-CD8 lineage 'choice' was mediated in part by direct positive regulation of the transcription factor Th-POK. Furthermore, loss of TCF-1 and LEF-1 unexpectedly caused derepression of CD4 expression in T cells committed to the CD8(+) lineage without affecting the expression of Runx transcription factors. Instead, TCF-1 physically interacted with Runx3 to cooperatively silence Cd4. Thus, TCF-1 and LEF-1 adopted distinct genetic 'wiring' to promote the CD4(+) T cell fate and establish CD8(+) T cell identity.

Linking GATA-3 and interleukin-13: implications in asthma

INTRODUCTION

Asthma is one of the serious global health problems and cause of huge mortality and morbidity. It is characterized by persistent airway inflammation, airway hyperresponsiveness, increased IgE levels and mucus hypersecretion. Asthma is mediated by dominant Th2 immune response, causing enhanced expression of Th2 cytokines. These cytokines are responsible for the various pathological changes associated with allergic asthma.

MATERIALS AND METHODS

The role of Th2 cells in the pathogenesis of the asthma is primarily mediated through the cytokine IL-13, also produced by type 2 innate lymphoid cells, that comes under the transcriptional regulation of GATA3. In this review we will try to explore the link between IL-13 and GATA3 in the progression and regulation of asthma and its possible role as a therapeutic target.

CONCLUSION

Inhibition of GATA3 activity or blockade of GATA3 expression may attenuate the interleukin-13 mediated asthma phenotypes. So, GATA3 might be a potential therapeutic target for the treatment of allergic asthma.

Stemness of T cells and the hematopoietic stem cells: fate, memory, niche, cytokines

Stem cells are able to generate both cells that differentiate and cells that remain undifferentiated but potentially have the same developmental program. The prolonged duration of the protective immune memory for infectious diseases such as polio, small pox, and measles, suggested that memory T cells may have stem cell properties. Understanding the molecular basis for the life-long persistence of memory T cells may be useful to project targeted therapies for immune deficiencies and infectious diseases and to formulate vaccines. In the last decade evidence from different laboratories shows that memory T cells may share self-renewal pathways with bone marrow hematopoietic stem cells. In stem cells the intrinsic self-renewal activity, which depends on gene expression, is known to be modulated by extrinsic signals from the environment that may be tissue specific. These extrinsic signals for stemness of memory T cells include cytokines such as IL-7 and IL-15 and there are other cytokine signals for maintaining the cytokine signature (TH1, TH2, etc.) of memory T cells. Intrinsic and extrinsic pathways that might be common to bone marrow hematopoietic stem cells and memory T lymphocytes are discussed and related to self-renewal functions.

Transcriptional control of CD4 and CD8 coreceptor expression during T cell development

The differentiation and function of peripheral helper and cytotoxic T cell lineages is coupled with the expression of CD4 and CD8 coreceptor molecules, respectively. This indicates that the control of coreceptor gene expression is closely linked with the regulation of CD4/CD8 lineage decision of DP thymocytes. Research performed during the last two decades revealed comprehensive mechanistic insight into the developmental stage- and subset/lineage-specific regulation of Cd4, Cd8a and Cd8b1 (Cd8) gene expression. These studies provided important insight into transcriptional control mechanisms during T cell development and into the regulation of cis-regulatory networks in general. Moreover, the identification of transcription factors involved in the regulation of CD4 and CD8 significantly advanced the knowledge of the transcription factor network regulating CD4/CD8 cell-fate choice of DP thymocytes. In this review, we provide an overview of the identification and characterization of CD4/CD8 cis-regulatory elements and present recent progress in our understanding of how these cis-regulatory elements control CD4/CD8 expression during T cell development and in peripheral T cells. In addition, we describe the transcription factors implicated in the regulation of coreceptor gene expression and discuss how these factors are integrated into the transcription factor network that regulates CD4/CD8 cell-fate choice of DP thymocytes.

Architecture of a lymphomyeloid developmental switch controlled by PU.1, Notch and Gata3

Hematopoiesis is a classic system with which to study developmental potentials and to investigate gene regulatory networks that control choices among alternate lineages. T-cell progenitors seeding the thymus retain several lineage potentials. The transcription factor PU.1 is involved in the decision to become a T cell or a myeloid cell, and the developmental outcome of expressing PU.1 is dependent on exposure to Notch signaling. PU.1-expressing T-cell progenitors without Notch signaling often adopt a myeloid program, whereas those exposed to Notch signals remain in a T-lineage pathway. Here, we show that Notch signaling does not alter PU.1 transcriptional activity by degradation/alteration of PU.1 protein. Instead, Notch signaling protects against the downregulation of T-cell factors so that a T-cell transcriptional network is maintained. Using an early T-cell line, we describe two branches of this network. The first involves inhibition of E-proteins by PU.1 and the resulting inhibition of Notch signaling target genes. Effects of E-protein inhibition can be reversed by exposure to Notch signaling. The second network is dependent on the ability of PU.1 to inhibit important T-cell transcription factor genes such as Myb, Tcf7 and Gata3 in the absence of Notch signaling. We show that maintenance of Gata3 protein levels by Myb and Notch signaling is linked to the ability to retain T-cell identity in response to PU.1.

Characterization and expression analysis of Th-POK from the Japanese pufferfish, Takifugu rubripes

In fish, T cell lineage commitment has not been studied, although there are reports related to CD4 and CD8 positive cells. This study describes the cloning and analysis of a master regulator involved in this process, the Th-POK gene in Japanese pufferfish, Takifugu rubripes. The Fugu Th-POK cDNA was composed of 1901 bp, with a 75 bp 5'-UTR, a 131 bp 3'-UTR, and a 1692 bp open reading frame which translates into a peptide of 564 amino acid residues. The deduced Fugu Th-POK protein contained a BTB/POZ domain, Krüppel motif (H/C linker) and Krüppel-like zinc finger DNA binding domain with C2H2 structure. The homology analysis of Fugu Th-POK (ZBTB7B) with other known ZBTB7 members (ZBTB7A, 7C) showed low identity, and the phylogenetic tree analysis showed the Fugu Th-POK clustered with the mammalian Th-POK, away from other ZBTB7 members. The analysis of transcriptional control region of Th-POK gene suggested that the 5'-flanking region and intron 1 include numerous canonical binding motifs for transcription factors regulating T cell development. The genomic organization of the Fugu Th-POK gene was composed of three exons and two introns, and its structure was identical to that of its human counterpart. Comparison of the Fugu and human genomes showed that high levels of conserved synteny existed around the Th-POK gene. The high expression of the Fugu Th-POK gene in unstimulated tissues was seen in head kidney, muscle, skin and gills. Moreover, the expression of the Fugu Th-POK gene in thymic cells was increased by LPS, polyI:C and PHA stimulation.

Association analyses identify multiple new lung cancer susceptibility loci and their interactions with smoking in the Chinese population

To find additional susceptibility loci for lung cancer, we tested promising associations from our previous genome-wide association study (GWAS) of lung cancer in the Chinese population in an extended validation sample size of 7,436 individuals with lung cancer (cases) and 7,483 controls. We found genome-wide significant (P < 5.0 × 10(-8)) evidence for three additional lung cancer susceptibility loci at 10p14 (rs1663689, close to GATA3, P = 2.84 × 10(-10)), 5q32 (rs2895680 in PPP2R2B-STK32A-DPYSL3, P = 6.60 × 10(-9)) and 20q13.2 (rs4809957 in CYP24A1, P = 1.20 × 10(-8)). We also found consistent associations for rs247008 at 5q31.1 (IL3-CSF2-P4HA2, P = 7.68 × 10(-8)) and rs9439519 at 1p36.32 (AJAP1-NPHP4, P = 3.65 × 10(-6)). Four of these loci showed evidence for interactions with smoking dose (P = 1.72 × 10(-10), P = 5.07 × 10(-3), P = 6.77 × 10(-3) and P = 4.49 × 10(-2) for rs2895680, rs4809957, rs247008 and rs9439519, respectively). These results advance our understanding of lung cancer susceptibility and highlight potential pathways that integrate genetic variants and smoking in the development of lung cancer.

MicroRNA miR-150 is involved in Vα14 invariant NKT cell development and function

CD1d-restricted Vα14 invariant NKT (iNKT) cells play an important role in the regulation of diverse immune responses. MicroRNA-mediated RNA interference is emerging as a crucial regulatory mechanism in the control of iNKT cell differentiation and function. Yet, roles of specific microRNAs in the development and function of iNKT cells remain to be further addressed. In this study, we identified the gradually increased expression of microRNA-150 (miR-150) during the maturation of iNKT cells in thymus. Using miR-150 knockout (KO) mice, we found that miR-150 deletion resulted in an interruption of iNKT cell final maturation in both thymus and periphery. Upon activation, iNKT cells from miR-150KO mice showed significantly increased IFN-γ production compared with wild-type iNKT cells. Bone marrow-transferring experiments demonstrated the cell-intrinsic characteristics of iNKT cell maturation and functional defects in mice lacking miR-150. Furthermore, miR-150 target c-Myb was significantly upregulated in miR-150KO iNKT cells, which potentially contribute to iNKT cell defects in miR-150KO mice. Our data define a specific role of miR-150 in the development and function of iNKT cells.

miR-150 regulates the development of NK and iNKT cells

Natural killer (NK) and invariant NK T (iNKT) cells are critical in host defense against pathogens and for the initiation of adaptive immune responses. miRNAs play important roles in NK and iNKT cell development, maturation, and function, but the roles of specific miRNAs are unclear. We show that modulation of miR-150 expression levels has a differential effect on NK and iNKT cell development. Mice with a targeted deletion of miR-150 have an impaired, cell lineage-intrinsic defect in their ability to generate mature NK cells. Conversely, a gain-of-function miR-150 transgene promotes the development of NK cells, which display a more mature phenotype and are more responsive to activation. In contrast, overexpression of miR-150 results in a substantial reduction of iNKT cells in the thymus and in the peripheral lymphoid organs. The transcription factor c-Myb has been shown to be a direct target of miR-150. Our finding of increased NK cell and decreased iNKT cell frequencies in Myb heterozygous bone marrow chimeras suggests that miR-150 differentially controls the development of NK and iNKT cell lineages by targeting c-Myb.

c-Myb and GATA-3 cooperatively regulate IL-13 expression via conserved GATA-3 response element and recruit mixed lineage leukemia (MLL) for histone modification of the IL-13 locus

The c-Myb and GATA-3 transcription factors play important roles in T cell development. We recently reported that c-Myb, GATA-3, and Menin form a core transcription complex that regulates GATA-3 expression and ultimately Th2 cell development in human peripheral blood T cells. However, c-Myb roles for Th2 cytokine expression were not demonstrated. In this article, we report that c-Myb and GATA-3 cooperatively play an essential role in IL-13 expression though direct binding to a conserved GATA-3 response element (CGRE), an enhancer for IL-13 expression. c-Myb and GATA-3 were shown to activate the CGRE-IL-13 promoter by ∼160-fold, and mutation of the canonical Myb binding site completely abrogated CGRE enhancer activity. In contrast, mutation of the GATA binding site partially decreased CGRE enhancer activity. GATA-3 did not bind to CGRE when c-myb expression was silenced. c-Myb, GATA-3, Menin, and mixed lineage leukemia (MLL) bound to CGRE in human primary CD4(+) effector/memory cells. Moreover, c-myb silencing significantly decreased both methylation of histone H3K4 and acetylation of histone H3K9 at the IL-13 locus in CD4(+) effector/memory cells. Therefore, in addition to the strong enhancer effect for the transcription of IL-13, the c-Myb/GATA-3 complex recruits MLL to the CGRE for histone modification of the IL-13 locus during the differentiation of memory Th2 cells.

On becoming a T cell, a convergence of factors kick it up a Notch along the way

The thymus is seeded by bone marrow-derived progenitors, which undergo a series of differentiation and proliferation events in order to generate functional T lymphocytes. The Notch signaling pathway, together with multiple transcription factors, act in concert to commit progenitors to a T-lineage fate, extinguishing non-T cell potential, inducing thymocyte differentiation and supporting proliferation and survival along the way to becoming a mature T cell. This review focuses on recent evidence regarding the complex interplay between the Notch pathway and other key transcription factors at specific lineage-decision points during the program of T cell development.

Regulatory gene network circuits underlying T cell development from multipotent progenitors

Regulatory gene circuits enable stem and progenitor cells to detect and process developmental signals and make irreversible fate commitment decisions. To gain insight into the gene circuits underlying T cell fate decision making in progenitor cells, we generated an updated T-lymphocyte developmental gene regulatory network from genes and connections found in the literature. This reconstruction allowed us to identify candidate regulatory gene circuit elements underlying T cell fate decision making. Here, we examine the roles of these circuits in facilitating different aspects of the decision making process, and discuss experiments to further probe their structure and function.

Transcriptional control of T-cell development

T lymphocytes, which are central players in orchestrating immune responses, consist of several subtypes with distinct functions. The thymus is an organ where hematopoietic progenitors undergo sequential developmental processes to give rise to this variety of T-cell subsets with diverse antigen specificity. In the periphery, naive T cells further differentiate into effector cells upon encountering antigens. There are several developmental checkpoints during T-cell development, where regulation by a combination of transcription factors imprints specific functional properties on precursors. The transcription factors E2A, GATA-binding protein 3 (Gata3) and RUNT-related transcription factor (Runx) are involved at various stages in the differentiation of double-negative thymocytes and in β-selection, as are transcription factors from the Notch signaling pathway; other transcription factors such as B-cell lymphoma/leukemia 11b (Bcl11b), myeloblastosis viral oncogene homolog (Myb) and inhibitor of DNA binding 3 (Id3) are involved at specific stages. Differentiation of T cells into helper versus cytotoxic cells involves not only antagonistic interplay between Runx and T(h) inducing POZ-Kruppel factor (ThPOK) but also complex interactions between MAZR, Gata3 and Myb in the activation and silencing of genes such as Cd4 and Cd8 as well as the gene that encodes ThPOK itself. A wide range of well-defined transcription factors, including signal transducer and activator of transcriptions (STATs), T-bet, Gata3, nuclear factor of activated T cell (NFAT), adaptor-related protein complex 1 (AP-1) and nuclear factor κB (NF-κB), are known to shape T(h)1/T(h)2 differentiation. Runx and Gata3 also operate in this process, as do c-Maf and recombining binding protein for immunoglobulin Jκ region (RBP-J) and the chromatin-reorganizing protein special AT-rich sequence-binding protein 1 (SATB1). In this review, we briefly discuss how T-cell characteristics are acquired and become divergent from the point of view of transcriptional regulation.

An NK and T cell enhancer lies 280 kilobase pairs 3' to the gata3 structural gene

Transcription factor GATA-3 is vital for multiple stages of T cell and natural killer (NK) cell development, and yet the factors that directly regulate Gata3 transcription during hematopoiesis are only marginally defined. Here, we show that neither of the Gata3 promoters, previously implicated in its tissue-specific regulation, is alone capable of directing Gata3 transcription in T lymphocytes. In contrast, by surveying large swaths of DNA surrounding the Gata3 locus, we located a cis element that can recapitulate aspects of the Gata3-dependent T cell regulatory program in vivo. This element, located 280 kbp 3' to the structural gene, directs both T cell- and NK cell-specific transcription in vivo but harbors no other tissue activity. This novel, distant element regulates multiple major developmental stages that require GATA-3 activity.

The enigma of CD4-lineage specification

CD4(+) T cells are essential for defenses against pathogens and affect the functions of most cells involved in the immune response. Although CD4(+) T cells generally recognize peptide antigens bound to MHC-II molecules, important subsets are restricted by other MHC or MHC-like molecules, including CD1d-restricted "invariant" iNK T cells. This review discusses recently identified nodes in the transcriptional circuits that are involved in controlling CD4(+) T-cell differentiation, notably the commitment factor Thpok and its interplay with Runx transcriptional regulators, and focuses on how transcription factors acting upstream of Thpok, including Gata3, Tox and E-box proteins, promote the emergence of CD4-lineage-specific gene expression patterns.

Regulation of GATA-3 expression during CD4 lineage differentiation

GATA-3 is necessary for the development of MHC class II-restricted CD4 T cells, and its expression is increased during positive selection of these cells. TCR signals drive this upregulation, but the signaling pathways that control this process are not well understood. Using genetic and pharmacological approaches, we show that GATA-3 upregulation during thymocyte-positive selection is the result of additive inputs from the Ras/MAPK and calcineurin pathways. This upregulation requires the presence of the transcription factor c-Myb. Furthermore, we show that TH-POK can also upregulate GATA-3 in double-positive thymocytes, suggesting the existence of a positive feedback loop that contributes to lock in the initial commitment to the CD4 lineage during differentiation.

Transcriptional and epigenetic regulation of CD4/CD8 lineage choice

The helper versus cytotoxic-lineage choice of CD4(+)CD8(+) DP thymocytes correlates with MHC restriction of their T cell receptors and the termination of either CD8 or CD4 coreceptor expression. It has been hypothesized that transcription factors regulating the expression of the Cd4/Cd8 coreceptor genes must play a role in regulating the lineage decision of DP thymocytes. Indeed, progress made during the past decade led to the identification of several transcription factors that regulate CD4/CD8 expression that are as well important regulators of helper/cytotoxic cell fate choice. These studies provided insight into the molecular link between the regulation of coreceptor expression and lineage decision. However, studies initiated by the identification of ThPOK, a central transcription factor for helper T cell development, have offered another perspective on the cross-regulation between these two processes. Here, we review advances in our understanding of regulatory circuits composed of transcription factors and their link to epigenetic mechanisms, which play essential roles in specifying and sealing cell lineage identity during the CD4/CD8 commitment process of DP thymocytes.

MYBBP1A: a new Ipr1's binding protein in mice

Infection with mycobacterium tuberculosis (MTB) can cause different outcomes in hosts with variant genetic backgrounds. Previously, we identified an intracellular pathogen resistance 1 (Ipr1) gene with the role of resistance of MTB infection in mice model. However, until now, its binding proteins have been little known even for its human homology, SP110. In this study, the homology for mouse Ipr1 in canines was found to have an extra domain structure, h.1.5.1. And 30 potential candidate proteins were predicted to bind canine Ipr1, which were characterized of the interacting structure with the h.1.5.1. Among them, MYBBP1A was verified to bind with both Ipr1 and eGFP-Ipr1 in mouse macrophage J774A.1 clone 21 cells using co-immunoprecipitation method. And with the constructed high-confidence Ipr1-involved network, we suggested that Ipr1 might be involved in apoptosis pathway via MYBBP1A.

A genome-wide association study of Hodgkin's lymphoma identifies new susceptibility loci at 2p16.1 (REL), 8q24.21 and 10p14 (GATA3)

To identify susceptibility loci for classical Hodgkin's lymphoma (cHL), we conducted a genome-wide association study of 589 individuals with cHL (cases) and 5,199 controls with validation in four independent samples totaling 2,057 cases and 3,416 controls. We identified three new susceptibility loci at 2p16.1 (rs1432295, REL, odds ratio (OR) = 1.22, combined P = 1.91 × 10(-8)), 8q24.21 (rs2019960, PVT1, OR = 1.33, combined P = 1.26 × 10(-13)) and 10p14 (rs501764, GATA3, OR = 1.25, combined P = 7.05 × 10(-8)). Furthermore, we confirmed the role of the major histocompatibility complex in disease etiology by revealing a strong human leukocyte antigen (HLA) association (rs6903608, OR = 1.70, combined P = 2.84 × 10(-50)). These data provide new insight into the pathogenesis of cHL.

From the cradle to the grave: activities of GATA-3 throughout T-cell development and differentiation

GATA family transcription factors play multiple vital roles in hematopoiesis in many cell lineages, and in particular, T cells require GATA-3 for execution of several developmental steps. Transcriptional activation of the Gata3 gene is observed throughout T-cell development and differentiation in a stage-specific fashion. GATA-3 has been described as a master regulator of T-helper 2 (Th2) cell differentiation in mature CD4(+) T cells. During T-cell development in the thymus, its roles in the CD4 versus CD8 lineage choice and at the β-selection checkpoint are the best characterized. In contrast, its importance prior to β-selection has been obscured both by the developmental heterogeneity of double negative (DN) 1 thymocytes and the paucity of early T-lineage progenitors (ETPs), a subpopulation of DN1 cells that contains the most immature thymic progenitors that retain potent T-lineage developmental potential. By examining multiple lines of in vivo evidence procured through the analysis of Gata3 mutant mice, we have recently demonstrated that GATA-3 is additionally required at the earliest stage of thymopoiesis for the development of the ETP population. Here, we review the characterized functions of GATA-3 at each stage of T-cell development and discuss hypothetical molecular pathways that mediate these functions.

Lymphocyte development requires S-nitrosoglutathione reductase

NO is critical to immunity, but its role in the development of the immune system is unknown. In this study, we show that S-nitrosoglutathione reductase (GSNOR), a protein key to the control of protein S-nitrosylation, is important for the development of lymphocytes. Genetic deletion of GSNOR in mice results in significant decrease in both T and B lymphocytes in the periphery. In thymus, GSNOR deficiency causes excessive protein S-nitrosylation, increases apoptosis, and reduces the number of CD4 single-positive thymocytes. Lymphopenia and increase in S-nitrosylation and apoptosis in GSNOR-deficient mice are largely abolished by genetic deletion of inducible NO synthase. Furthermore, the protection of lymphocyte development by GSNOR is apparently intrinsic to hematopoietic cells. Thus, GSNOR, likely through regulation of S-nitrosylation and apoptosis, physiologically plays a protective role in the development of the immune system.

The network of transcription factors that underlie the CD4 versus CD8 lineage decision

Virtually all mature T cells are CD4(+)CD8(-) or CD4(-)CD8(+) and this not only is their most important surface-phenotype distinction but also has crucial functional consequences for the entire immune response. Both subsets arise from double-positive thymocytes, and much has been learned about the molecular events that govern this lineage bifurcation process. As detailed in this review, the signaling pathways and specific molecules that control this process are now being discovered. In particular, the transcription factors ThPOK (T-helper inducing POZ-Kruppel factor) and Runx3 have emerged as the crucial regulators of helper lineage commitment and the cytotoxic lineage, respectively. This article describes their antagonistic interaction that is an important mechanism of the lineage specification, as well as the hierarchy and importance of several other transcription factors and cytokine signals in the network of pathways that govern thymocyte helper/cytotoxic lineage commitment.

c-Myb, Menin, GATA-3, and MLL form a dynamic transcription complex that plays a pivotal role in human T helper type 2 cell development

GATA-3 and c-Myb are core elements of a transcriptionally active complex essential for human Th2 cell development and maintenance. We report herein mechanistic details concerning the role of these transcription factors in human peripheral blood Th2 cell development. Silencing c-Myb in normal human naive CD4(+) cells under Th2 cell-promoting conditions blocked up-regulation of GATA-3 and interleukin-4, and in effector/memory CD4(+) T cells, decreased expression of GATA-3 and Th2 cytokines. In primary T cells, c-Myb allows GATA-3 to autoactivate its own expression, an event that requires the direct interaction of c-Myb and GATA-3 on their respective binding sites in promoter of GATA-3. Immunoprecipitation revealed that the c-Myb/GATA-3 complex contained Menin and mixed lineage leukemia (MLL). MLL recruitment into the c-Myb-GATA-3-Menin complex was associated with the formation Th2 memory cells. That MLL-driven epigenetic changes were mechanistically important for this transition was suggested by the fact that silencing c-Myb significantly decreased the methylation of histone H3K4 and the acetylation of histone H3K9 at the GATA-3 locus in developing Th2 and CD4(+) effector/memory cells. Therefore, c-Myb, GATA-3, and Menin form a core transcription complex that regulates GATA-3 expression and, with the recruitment of MLL, Th2 cell maturation in primary human peripheral blood T cells.

The transcription factor c-Myb primes CD4+CD8+ immature thymocytes for selection into the iNKT lineage

Type I invariant NKT cells (iNKT cells) are a subset of alphabeta T cells characterized by the expression of an invariant alpha-chain variable region 14-alpha-chain joining region 18 (V(alpha)14J(alpha)18) T cell antigen receptor (TCR) alpha-chain. The iNKT cells derive from CD4(+)CD8(+) double-positive (DP) thymocytes, and their generation requires a long half-life of DP thymocytes to allow V(alpha)14-J(alpha)18 rearrangements, expression of glycolipid-loaded CD1d on DP thymocytes, and signaling through the signaling-activation molecule SLAM-adaptor SAP pathway. Here we show that the transcription factor c-Myb has a central role in priming DP thymocytes to enter the iNKT lineage by simultaneously regulating CD1d expression, the half-life of DP cells and expression of SLAMF1, SLAMF6 and SAP.

c-Myb promotes the survival of CD4+CD8+ double-positive thymocytes through upregulation of Bcl-xL

Mechanisms that regulate the lifespan of CD4(+)CD8(+) double-positive (DP) thymocytes help shape the peripheral T cell repertoire. However, the molecular mechanisms controlling DP thymocyte survival remain poorly understood. The Myb proto-oncogene encodes a transcription factor required during multiple stages of T cell development. We demonstrate that Myb mRNA expression is upregulated as thymocytes differentiate from the double-negative into the metabolically quiescent, small, preselection DP stage during T cell development. Using a conditional deletion mouse model, we demonstrate that Myb-deficient DP thymocytes undergo premature apoptosis, resulting in a limited Tcralpha repertoire biased toward 5' Jalpha segment usage. Premature apoptosis occurs specifically in the small preselection DP compartment in an alphabetaTCR-independent manner and is a consequence of decreased Bcl-xL expression. Forced Bcl-xL expression is able to rescue survival, and reintroduction of c-Myb restores both Bcl-xL expression and the small preselection DP compartment. We further demonstrate that c-Myb promotes transcription at the Bcl2l1 locus via a genetic pathway that is independent of the expression of T cell-specific factor-1 or RORgammat, two transcription factors that induce Bcl-xL expression in T cell development. Thus, Bcl-xL is a novel mediator of c-Myb activity during normal T cell development.

CD4-CD8 lineage differentiation: Thpok-ing into the nucleus

The mature alphabeta T cell population is divided into two main lineages that are defined by the mutually exclusive expression of CD4 and CD8 surface molecules (coreceptors) and that differ in their MHC restriction and function. CD4 T cells are typically MHC-II restricted and helper (or regulatory), whereas CD8 T cells are typically cytotoxic. Several transcription factors are known to control the emergence of CD4 and CD8 lineages, including the zinc finger proteins Thpok and Gata3, which are required for CD4 lineage differentiation, and the Runx factors Runx1 and Runx3, which contribute to CD8 lineage differentiation. This review summarizes recent advances on the function of these transcription factors in lineage differentiation. We also discuss how the "circuitry" connecting these factors could operate to match the expression of the lineage-committing factors Thpok and Runx3, and therefore lineage differentiation, to MHC specificity.