A B-cell coactivator of octamer-binding transcription factors

Optimal CXCR5 Expression during Tfh Maturation Involves the Bhlhe40-Pou2af1 Axis

The pair of transcription factors Bcl6-Blimp1 is well-known for follicular T helper (Tfh) cell fate determination, however, the mechanism(s) for Bcl6-independent regulation of CXCR5 during Tfh migration into germinal center (GC) is still unclear. In this study, we uncovered another pair of transcription factors, Bhlhe40-Pou2af1, that regulates CXCR5 expression. Pou2af1 was specifically expressed in Tfh cells whereas Bhlhe40 expression was found high in non-Tfh cells. Pou2af1 promoted Tfh formation and migration into GC by upregulating CXCR5 but not Bcl6, while Bhlhe40 repressed this process by inhibiting Pou2af1 expression. RNA-Seq analysis of antigen-specific Tfh cells generated in vivo confirmed the role of Bhlhe40-Pou2af1 axis in regulating optimal CXCR5 expression. Thus, the regulation of CXCR5 expression and migration of Tfh cells into GC involves a transcriptional regulatory circuit consisting of Bhlhe40 and Pou2af1, which operates independent of the Bcl6-Blimp1 circuit that determines the Tfh cell fate.

Transcriptional Coactivator BOB1 (OBF1, OCA-B) Modulates the Specificity of DNA Recognition by the POU-Domain Factors OCT1 and OCT2 in a Monomeric Configuration

BOB1, a mammalian lymphocyte-specific transcriptional coactivator of the transcription factors OCT1 and OCT2 (OCT1/2), plays important roles in normal immune responses, autoimmunity, and hematologic malignancies. The issue of a DNA sequence preference change imposed by BOB1 was raised more than two decades ago but remains unresolved. In this paper, using the EMSA-SELEX-Seq approach, we have reassessed the intrinsic ability of BOB1 to modulate the specificity of DNA recognition by OCT1 and OCT2. Our results have reaffirmed previous conclusions regarding BOB1 selectivity towards the dimer configuration of OCT1/2. However, they suggest that the monomeric configuration of these factors, assembled on the classical octamer ATGCAAAT and related motifs, are the primary targets of BOB1. Our data further specify the DNA sequence preference imposed by BOB1 and predict the probability of ternary complex formation. These results provide an additional insight into the action of BOB1-an essential immune regulator and a promising molecular target for the treatment of autoimmune diseases and hematologic malignancies.

The Role of the Transcriptional Coactivator BOB.1/OBF.1 in Adaptive Immunity

BOB.1/OBF.1 is a transcriptional coactivator involved in octamer-dependent transcription. Thereby, BOB.1/OBF.1 is involved in the transcriptional regulation of genes important for lymphocyte physiology. BOB.1/OBF.1-deficient mice reveal multiple B- and T-cell developmental defects. The most prominent defect of these mice is the complete absence of germinal centers (GCs) resulting in severely impaired T-cell-dependent immune responses. In humans, BOB.1/OBF.1 is associated with several autoimmune and inflammatory diseases but also linked to liquid and solid tumors. Although its role for B-cell development is relatively well understood, its exact role for the GC reaction and T-cell biology has long been unclear. Here, the contribution of BOB.1/OBF.1 for B-cell maturation is summarized, and recent findings regarding its function in GC B- as well as in various T-cell populations are discussed. Finally, a detailed perspective on how BOB.1/OBF.1 contributes to different pathologies is provided.

POU2AF2/C11orf53 functions as a coactivator of POU2F3 by maintaining chromatin accessibility and enhancer activity

Small cell lung cancer (SCLC), accounting for around 13% of all lung cancers, often results in rapid tumor growth, early metastasis, and acquired therapeutic resistance. The POU class 2 homeobox 3 (POU2F3) is a master regulator of tuft cell identity and defines the SCLC-P subtype that lacks the neuroendocrine markers. Here, we have identified a previously uncharacterized protein, C11orf53, which is coexpressed with POU2F3 in both SCLC cell lines and patient samples. Mechanistically, C11orf53 directly interacts with POU2F3 and is recruited to chromatin by POU2F3. Depletion of C11orf53 reduced enhancer H3K27ac levels and chromatin accessibility, resulting in a reduction of POU2F3-dependent gene expression. On the basis of the molecular function of C11orf53, we renamed it as "POU Class 2 Homeobox Associating Factor 2" (POU2AF2). In summary, our study has identified a new coactivator of POU2F3 and sheds light on the therapeutic potential of targeting POU2AF2/POU2F3 heterodimer in human SCLC.

BOB.1/OBF.1 is required during B-cell ontogeny for B-cell differentiation and germinal center function

BOB.1/OBF.1 is a lymphocyte-specific transcriptional co-activator of octamer-dependent transcription. It regulates the expression of genes important for lymphocyte physiology together with the Oct-1 and Oct-2 transcription factors. So far, BOB.1/OBF.1 has been studied in conventional knockout mice, whereby a function of BOB.1/OBF.1 in B but also in T cells was described. The main characteristic of BOB.1/OBF.1-deficient mice is the complete absence of germinal centers. However, it is entirely unsolved at which stage of B-cell development BOB.1/OBF.1 expression is essential for germinal center formation. Still, it is not known whether defects observed late in B-cell development of BOB.1/OBF.1-deficient mice are merely a consequence of defective early B-cell development. To answer the question, whether BOB.1/OBF.1 expression is required before or during the process of germinal center formation, we established a mouse system, which allows the conditional deletion of BOB.1/OBF.1 at different stages of B-cell development. Our data reveal a requirement for BOB.1/OBF.1 during both early antigen-independent and late antigen-dependent B-cell development, and further a requirement for efficient germinal center reaction during complete B-cell ontogeny. By specifically deleting BOB.1/OBF.1 in germinal center B cells, we provide evidence that the failure to form germinal centers is a germinal center B-cell intrinsic defect and not exclusively a consequence of defective early B-cell maturation.

OCT2 pre-positioning facilitates cell fate transition and chromatin architecture changes in humoral immunity

During the germinal center (GC) reaction, B cells undergo profound transcriptional, epigenetic and genomic architectural changes. How such changes are established remains unknown. Mapping chromatin accessibility during the humoral immune response, we show that OCT2 was the dominant transcription factor linked to differential accessibility of GC regulatory elements. Silent chromatin regions destined to become GC-specific super-enhancers (SEs) contained pre-positioned OCT2-binding sites in naive B cells (NBs). These preloaded SE 'seeds' featured spatial clustering of regulatory elements enriched in OCT2 DNA-binding motifs that became heavily loaded with OCT2 and its GC-specific coactivator OCAB in GC B cells (GCBs). SEs with high abundance of pre-positioned OCT2 binding preferentially formed long-range chromatin contacts in GCs, to support expression of GC-specifying factors. Gain in accessibility and architectural interactivity of these regions were dependent on recruitment of OCAB. Pre-positioning key regulators at SEs may represent a broadly used strategy for facilitating rapid cell fate transitions.

The regulation and function of CD20: an "enigma" of B-cell biology and targeted therapy

The introduction of anti-CD20 monoclonal antibodies such as rituximab, ofatumumab, or obinutuzumab improved the therapy of B-cell malignancies even though the precise physiological role and regulation of CD20 remains unclear. Furthermore, CD20 expression is highly variable between different B-cell malignancies, patients with the same malignancy, and even between intraclonal subpopulations in an individual patient. Several epigenetic (EZH2, HDAC1/2, HDAC1/4, HDAC6, complex Sin3A-HDAC1) and transcription factors (USF, OCT1/2, PU.1, PiP, ELK1, ETS1, SP1, NFκB, FOXO1, CREM, SMAD2/3) regulating CD20 expression (encoded by MS4A1) have been characterized. CD20 is induced in the context of microenvironmental interactions by CXCR4/SDF1 (CXCL12) chemokine signaling and the molecular function of CD20 has been linked to the signaling propensity of B-cell receptor (BCR). CD20 has also been shown to interact with multiple other surface proteins on B cells (such as CD40, MHCII, CD53, CD81, CD82, and CBP). Current efforts to combine anti-CD20 monoclonal antibodies with BCR signaling inhibitors targeting BTK or PI3K (ibrutinib, acalabrutinib, idelalisib, duvelisib) or BH3-mimetics (venetoclax) lead to the necessity to better understand both the mechanisms of regulation and the biological functions of CD20. This is underscored by the observation that CD20 is decreased in response to the "BCR inhibitor" ibrutinib which largely prevents its successful combination with rituximab. Several small molecules (such as histone deacetylase inhibitors, DNA methyl-transferase inhibitors, aurora kinase A/B inhibitors, farnesyltransferase inhibitors, FOXO1 inhibitors, and bryostatin-1) are being tested to upregulate cell-surface CD20 levels and increase the efficacy of anti-CD20 monoclonal antibodies. Herein, we review the current understanding of CD20 function, and the mechanisms of its regulation in normal and malignant B cells, highlighting the therapeutic implications.

Transcriptional regulator BOB.1: Molecular mechanisms and emerging role in chronic inflammation and autoimmunity

Lymphocytes constitute an essential and potent effector compartment of the immune system. Therefore, their development and functions must be strictly regulated to avoid inappropriate immune responses, such as autoimmune reactions. Several lines of evidence from genetics (e.g. association with multiple sclerosis and primary biliary cirrhosis), human expression studies (e.g. increased expression in target tissues and draining lymph nodes of patients with autoimmune diseases), animal models (e.g. loss of functional protein protects animals from the development of collagen-induced arthritis, experimental autoimmune encephalomyelitis, type 1 diabetes, bleomycin-induced fibrosis) strongly support a causal link between the aberrant expression of the lymphocyte-restricted transcriptional regulator BOB.1 and the development of autoimmune diseases. In this review, we summarize the current knowledge of unusual structural and functional plasticity of BOB.1, stringent regulation of its expression, and the pivotal role that BOB.1 plays in shaping B- and T-cell responses. We discuss recent developments highlighting the significant contribution of BOB.1 to the pathogenesis of autoimmune diseases and how to leverage our knowledge to target this regulator to treat autoimmune tissue inflammation.

Type I collagen deletion in αSMA+ myofibroblasts augments immune suppression and accelerates progression of pancreatic cancer

Stromal desmoplastic reaction in pancreatic ductal adenocarcinoma (PDAC) involves significant accumulation of type I collagen (Col1). However, the precise molecular and mechanistic contribution of Col1 in PDAC progression remains unknown. Activated pancreatic stellate cells/αSMA+ myofibroblasts are major contributors of Col1 in the PDAC stroma. We use a dual-recombinase genetic mouse model of spontaneous PDAC to delete Col1 specifically in myofibroblasts. This results in significant reduction of total stromal Col1 content and accelerates the emergence of PanINs and PDAC, decreasing overall survival. Col1 deletion leads to Cxcl5 upregulation in cancer cells via SOX9. Increase in Cxcl5 is associated with recruitment of myeloid-derived suppressor cells and suppression of CD8+ T cells, which can be attenuated with combined targeting of CXCR2 and CCR2 to restrain accelerated PDAC progression in the setting of stromal Col1 deletion. Our results unravel the fundamental role of myofibroblast-derived Co1l in regulating tumor immunity and restraining PDAC progression.

Compartments and Connections Within the Germinal Center

Protective high affinity antibody responses emerge through an orchestrated developmental process that occurs in germinal centers (GCs). While GCs have been appreciated since 1930, a wealth of recent progress provides new insights into the molecular and cellular dynamics governing humoral immunity. In this review, we highlight advances that demonstrate that fundamental GC B cell function, selection, proliferation and SHM occur within distinct cell states. The resulting new model provides new opportunities to understand the evolution of immunity in infectious, autoimmune and neoplastic diseases.

Targeting transcriptional coregulator OCA-B/Pou2af1 blocks activated autoreactive T cells in the pancreas and type 1 diabetes

The transcriptional coregulator OCA-B promotes expression of T cell target genes in cases of repeated antigen exposure, a necessary feature of autoimmunity. We hypothesized that T cell-specific OCA-B deletion and pharmacologic OCA-B inhibition would protect mice from autoimmune diabetes. We developed an Ocab conditional allele and backcrossed it onto a diabetes-prone NOD/ShiLtJ strain background. T cell-specific OCA-B loss protected mice from spontaneous disease. Protection was associated with large reductions in islet CD8+ T cell receptor specificities associated with diabetes pathogenesis. CD4+ clones associated with diabetes were present but associated with anergic phenotypes. The protective effect of OCA-B loss was recapitulated using autoantigen-specific NY8.3 mice but diminished in monoclonal models specific to artificial or neoantigens. Rationally designed membrane-penetrating OCA-B peptide inhibitors normalized glucose levels and reduced T cell infiltration and proinflammatory cytokine expression in newly diabetic NOD mice. Together, the results indicate that OCA-B is a potent autoimmune regulator and a promising target for pharmacologic inhibition.

Development and application of a recombination-based library versus library high- throughput yeast two-hybrid (RLL-Y2H) screening system

Protein-protein interaction (PPI) network maintains proper function of all organisms. Simple high-throughput technologies are desperately needed to delineate the landscape of PPI networks. While recent state-of-the-art yeast two-hybrid (Y2H) systems improved screening efficiency, either individual colony isolation, library preparation arrays, gene barcoding or massive sequencing are still required. Here, we developed a recombination-based 'library vs library' Y2H system (RLL-Y2H), by which multi-library screening can be accomplished in a single pool without any individual treatment. This system is based on the phiC31 integrase-mediated integration between bait and prey plasmids. The integrated fragments were digested by MmeI and subjected to deep sequencing to decode the interaction matrix. We applied this system to decipher the trans-kingdom interactome between Mycobacterium tuberculosis and host cells and further identified Rv2427c interfering with the phagosome-lysosome fusion. This concept can also be applied to other systems to screen protein-RNA and protein-DNA interactions and delineate signaling landscape in cells.

Oct2 and Bob1 are sensitive and specific markers in lineage determination of B cell lymphomas with no expression of conventional B cell markers

AIMS

Rare cases of B cell lymphomas do not express conventional B cell markers (CD20, CD79a and PAX5), and these types of lymphomas include anaplastic lymphoma kinase (ALK)-positive large B cell lymphoma, plasmablastic lymphoma, primary effusion lymphoma and the solid variant of primary effusion lymphoma, extracavitary human herpesvirus 8 (HHV8)-positive large B cell lymphoma. Establishing accurate diagnoses of these B cell lymphomas can be challenging, and often requires a large panel of immunohistochemical stains, molecular assays and cytogenetic studies. B cell-specific transcription factors, Oct2 and Bob1, have been shown to be expressed consistently in most, if not all, B cell lymphomas, and therefore we investigated the utility of Oct2 and Bob1 immunohistochemistry in lineage determination of the aforementioned B cell lymphomas.

METHODS AND RESULTS

We selected 34 cases of previously diagnosed B cell lymphomas with no or weak expression of CD20, CD79a and PAX5. Oct2 and Bob1 were positive in 74% (25 of 34) and 85% (29 of 34) of the cases, respectively. When we combined the results of these two immunostains, 94% (32 of 34) cases expressed at least one of these two markers. We also included 51 control cases of non-B cell neoplasms, and none of them expressed either Oct2 or Bob1.

CONCLUSIONS

Oct2 and Bob1 are very reliable in determining B cell lineage in the absence of expression of other pan-B cell markers, and it should provide great diagnostic benefit to include them both in a panel of immunohistochemistry to assess undifferentiated malignant neoplasms.

Regulation of normal B-cell differentiation and malignant B-cell survival by OCT2

The requirement for the B-cell transcription factor OCT2 (octamer-binding protein 2, encoded by Pou2f2) in germinal center B cells has proved controversial. Here, we report that germinal center B cells are formed normally after depletion of OCT2 in a conditional knockout mouse, but their proliferation is reduced and in vivo differentiation to antibody-secreting plasma cells is blocked. This finding led us to examine the role of OCT2 in germinal center-derived lymphomas. shRNA knockdown showed that almost all diffuse large B-cell lymphoma (DLBCL) cell lines are addicted to the expression of OCT2 and its coactivator OCA-B. Genome-wide chromatin immunoprecipitation (ChIP) analysis and gene-expression profiling revealed the broad transcriptional program regulated by OCT2 that includes the expression of STAT3, IL-10, ELL2, XBP1, MYC, TERT, and ADA. Importantly, genetic alteration of OCT2 is not a requirement for cellular addiction in DLBCL. However, we detected amplifications of the POU2F2 locus in DLBCL tumor biopsies and a recurrent mutation of threonine 223 in the DNA-binding domain of OCT2. This neomorphic mutation subtly alters the DNA-binding preference of OCT2, leading to the transactivation of noncanonical target genes including HIF1a and FCRL3 Finally, by introducing mutations designed to disrupt the OCT2-OCA-B interface, we reveal a requirement for this protein-protein interface that ultimately might be exploited therapeutically. Our findings, combined with the predominantly B-cell-restricted expression of OCT2 and the absence of a systemic phenotype in our knockout mice, suggest that an OCT2-targeted therapeutic strategy would be efficacious in both major subtypes of DLBCL while avoiding systemic toxicity.

Anti-inflammatory cytokine interleukin-4 inhibits inducible nitric oxide synthase gene expression in the mouse macrophage cell line RAW264.7 through the repression of octamer-dependent transcription

Inducible nitric oxide synthase (iNOS) is a signature molecule involved in the classical activation of M1 macrophages and is induced by the Nos2 gene upon stimulation with Th1-cell derived interferon-gamma (IFNγ) and bacterial lipopolysaccharide (LPS). Although the anti-inflammatory cytokine IL-4 is known to inhibit Nos2 gene expression, the molecular mechanism involved in the negative regulation of Nos2 by IL-4 remains to be fully elucidated. In the present study, we investigated the mechanism of IL-4-mediated Nos2 transcriptional repression in the mouse macrophage-like cell line RAW264.7. Signal transducer and activator of transcription 6 (Stat6) knockdown by siRNA abolished the IL-4-mediated inhibition of Nos2 induced by IFNγ/LPS. Transient transfection of a luciferase reporter gene containing the 5′-flanking region of the Nos2 gene demonstrated that an octamer transcription factor (OCT) binding site in the promoter region is required for both positive regulation by IFNγ/LPS and negative regulation by IL-4. Although IL-4 had no inhibitory effect on the DNA-binding activity of constitutively expressed Oct-1, IL-4-induced Nos2-reporter transcriptional repression was partially attenuated by overexpression of the coactivator CREB-binding protein (CBP). These results suggest that a coactivator/cofactor that functionally interacts with Oct-1 is a molecular target for the IL-4-mediated inhibition of Nos2 and that IL-4-activated Stat6 represses Oct-1-dependent transcription by competing with this coactivator/cofactor.

A C-terminal acidic domain regulates degradation of the transcriptional coactivator Bob1

Bob1 (Obf-1 or OCA-B) is a 34-kDa transcriptional coactivator encoded by the Pou2af1 gene that is essential for normal B-cell development and immune responses in mice. During lymphocyte activation, Bob1 protein levels dramatically increase independently of mRNA levels, suggesting that the stability of Bob1 is regulated. We used a fluorescent protein-based reporter system to analyze protein stability in response to genetic and physiological perturbations and show that, while Bob1 degradation is proteasome mediated, it does not require ubiquitination of Bob1. Furthermore, degradation of Bob1 in B cells appears to be largely independent of the E3 ubiquitin ligase Siah. We propose a novel mechanism of Bob1 turnover in B cells, whereby an acidic region in the C terminus of Bob1 regulates the activity of degron signals elsewhere in the protein. Changes that make the C terminus more acidic, including tyrosine phosphorylation-mimetic mutations, stabilize the instable murine Bob1 protein, indicating that B cells may regulate Bob1 stability and activity via signaling pathways. Finally, we show that expressing a stable Bob1 mutant in B cells suppresses cell proliferation and induces changes in surface marker expression commonly seen during B-cell differentiation.

A novel SATB1 binding site in the BCL2 promoter region possesses transcriptional regulatory function

BCL2 is a key regulator of apoptosis. Our previous work has demonstrated that special AT-rich sequence-binding protein 1 (SATB1) is positively correlated with BCL2 expression. In the present study, we report a new SATB1 binding site located between P1 and P2 promoters of the BCL2 gene. The candidate SATB1 binding sequence predicted by bioinformatic analysis was investigated in vitro and in vivo by electrophoretic gel mobility shift assays (EMSA) and chromatin immunoprecipitation (ChIP). One 25-bp sequence, named SB1, was confirmed to be SATB1 binding site. The regulatory function of SB1 and its relevance to SATB1 were further examed with dual-luciferase reporter assay system in Jurkat cells. We found that SB1 could negatively regulate reporter gene activity. Mutation of SATB1 binding site further repressed the activity. Knockdown of SATB1 also enhanced this negative effect of SB1. Our data indicate that the SB1 sequence possesses negative transcriptional regulatory function and this function can be antagonized by SATB1.

Octamer-dependent transcription in T cells is mediated by NFAT and NF-κB

The transcriptional co-activator BOB.1/OBF.1 was originally identified in B cells and is constitutively expressed throughout B cell development. BOB.1/OBF.1 associates with the transcription factors Oct1 and Oct2, thereby enhancing octamer-dependent transcription. In contrast, in T cells, BOB.1/OBF.1 expression is inducible by treatment of cells with PMA/Ionomycin or by antigen receptor engagement, indicating a marked difference in the regulation of BOB.1/OBF.1 expression in B versus T cells. The molecular mechanisms underlying the differential expression of BOB.1/OBF.1 in T and B cells remain largely unknown. Therefore, the present study focuses on mechanisms controlling the transcriptional regulation of BOB.1/OBF.1 and Oct2 in T cells. We show that both calcineurin- and NF-κB-inhibitors efficiently attenuate the expression of BOB.1/OBF.1 and Oct2 in T cells. In silico analyses of the BOB.1/OBF.1 promoter revealed the presence of previously unappreciated combined NFAT/NF-κB sites. An array of genetic and biochemical analyses illustrates the involvement of the Ca²⁺/calmodulin-dependent phosphatase calcineurin as well as NFAT and NF-κB transcription factors in the transcriptional regulation of octamer-dependent transcription in T cells. Conclusively, impaired expression of BOB.1/OBF.1 and Oct2 and therefore a hampered octamer-dependent transcription may participate in T cell-mediated immunodeficiency caused by the deletion of NFAT or NF-κB transcription factors.

Direct interactions of OCA-B and TFII-I regulate immunoglobulin heavy-chain gene transcription by facilitating enhancer-promoter communication

B cell-specific coactivator OCA-B, together with Oct-1/2, binds to octamer sites in promoters and enhancers to activate transcription of immunoglobulin (Ig) genes, although the mechanisms underlying their roles in enhancer-promoter communication are unknown. Here, we demonstrate a direct interaction of OCA-B with transcription factor TFII-I, which binds to DICE elements in Igh promoters, that affects transcription at two levels. First, OCA-B relieves HDAC3-mediated Igh promoter repression by competing with HDAC3 for binding to promoter-bound TFII-I. Second, and most importantly, Igh 3' enhancer-bound OCA-B and promoter-bound TFII-I mediate promoter-enhancer interactions, in both cis and trans, that are important for Igh transcription. These and other results reveal an important function for OCA-B in Igh 3' enhancer function in vivo and strongly favor an enhancer mechanism involving looping and facilitated factor recruitment rather than a tracking mechanism.

A far-upstream Oct-1 motif regulates cytokine-induced transcription of the human inducible nitric oxide synthase gene

Transcriptional regulation of the human inducible nitric oxide synthase (hiNOS) gene is highly complex and requires an orchestrated flow of positive and negative transcription factors that bind to specific cis-acting upstream response elements. Very little specific information exists about the far-upstream region of the hiNOS gene. Oct-1 protein belongs to the Pit-Oct-Unc domain transcription factor family and is constitutively expressed in all dividing cells. It is essential for proliferation, differentiation, and other key cell processes. However, the role of Oct-1 in regulating hiNOS gene expression has not been reported. In this work, the octamer sequence 5'-ATGCAAAT-3' at -10.2 kb in the hiNOS promoter was identified as high-affinity Oct-1 binding by electrophoretic mobility shift assay in vitro and chromatin immunoprecipitation assay in vivo. Mutation of Oct-1 motif at -10.2 kb in the hiNOS promoter decreased cytokine-induced hiNOS promoter activity by 40%. Cytokine-induced hiNOS promoter activity was also significantly reduced by Oct-1 small interfering RNA targeting. Overexpression of Oct-1 increased cytokine-induced hiNOS protein expression in primary human hepatocytes. Furthermore, the Oct-1 motif at -10.2 kb of the hiNOS promoter conferred increased transcriptional activity to the heterologous thymidine kinase promoter irrespective of cytokine induction. Taken together, this work identifies a far-upstream functional Oct-1 enhancer motif at -10.2 kb in the hiNOS promoter that regulates cytokine-induced hiNOS gene transcription and further underscores tight control mechanisms regulating the expression of the hiNOS gene.

Role of defective Oct-2 and OCA-B expression in immunoglobulin production and Kaposi's sarcoma-associated herpesvirus lytic reactivation in primary effusion lymphoma

Primary effusion lymphoma (PEL) is a distinct type of B-cell non-Hodgkin lymphoma characterized by the presence of Kaposi's sarcoma-associated herpesvirus (KSHV/human herpesvirus 8). Despite having a genotype and gene expression signature of highly differentiated B cells, PEL does not usually express surface or cytoplasmic immunoglobulin (Ig). We show the lack of Oct-2 and OCA-B transcription factors to be responsible, at least in part, for this defect in Ig production. Like Ig genes, ORF50, the key regulator of the switch from latency to lytic reactivation, contains an octamer motif within its promoter. We therefore examined the impact of Oct-2 and OCA-B on ORF50 activation. The binding of Oct-1 to the ORF50 promoter has been shown to significantly enhance ORF50 transactivation. We found that Oct-2, on the other hand, inhibited ORF50 expression and consequently lytic reactivation by competing with Oct-1 for the octamer motif in the ORF50 promoter. Our data suggest that Oct-2 downregulation in infected cells would be favorable to KSHV in allowing for efficient viral reactivation.

BOB.1 of the channel catfish, Ictalurus punctatus: not a transcriptional coactivator?

Expression of the immunoglobulin heavy chain (IGH) locus of the channel catfish (Ictalurus punctatus) is driven by the Emu3' enhancer, whose core region contains two octamer motifs and a muE5 site. Orthologues of the Oct1 and Oct2 transcription factors have been cloned in the channel catfish and shown to bind to the octamer motifs within the core enhancer. While catfish Oct2 is an activator of transcription, catfish Oct1 failed to drive transcription and may act as a negative regulator of IGH transcription. In mammals, the Oct co-activator BOB.1 (B cell Oct-binding protein1, also known as OCA-B and OBF-1) greatly enhances the transcriptional activity of Oct factors and plays an important role in the development of the immune system. An orthologue of BOB.1 has been cloned in the catfish, and its function characterized. The POU binding domain of the catfish BOB.1 was found to be 95% identical at the amino acid level with the binding domain of human BOB.1, and all the residues directly involved in binding to the Oct-DNA complex were conserved. Despite this conservation, catfish BOB.1 failed to enhance transcriptional activation mediated by endogenous or co-transfected catfish Oct2, and failed to rescue the activity of the inactive catfish Oct1. Electrophoretic mobility shift assays showed that catfish BOB.1 was capable of binding both catfish Oct1 and Oct2 when they formed a complex with the Oct motif. Analysis of recombinant chimeric catfish and human BOB.1 proteins demonstrated that the failure to drive transcription was due to the lack of a functional activation domain within the catfish BOB.1.

Oct-1 induces pituitary tumor transforming gene expression in endocrine tumors

As human pituitary tumor transforming gene (hPTTG1) is upregulated in endocrine tumors, we studied regulatory mechanisms for hPTTG1 expression. We identified Oct-1-binding motifs in the hPTTG1 promoter region and show Oct-1-specific binding to the hPTTG1 promoter using chromatin immunoprecipitation. We overexpressed Oct-1 and observed approximately 2.5-fold activation of hPTTG1 promoter luciferase constructs (-2642/-1 and -1717/-1). Transcriptional activation was abrogated by co-transfection of an inactive Oct-1 form lacking the POU domain or by utilizing mutated hPTTG1 promoters or mutants devoid of two Oct-1-binding motifs (-1717/-1mut, -637/-1 or -433/-1). Using biotin-streptavidin pull-down assays, we confirmed Oct-1 binding to the two octamer motifs in the hPTTG1 promoter (-1669/-1631 and -1401/-1361). Endogenous hPTTG1 mRNA and protein increased up to approximately fourfold in Oct-1 transfectants, as measured by real-time PCR and western blot. In contrast, siRNA-mediated suppression of endogenous Oct-1 attenuated both the hPTTG1 mRNA and protein levels. Using confocal immunofluorescence imaging, Oct-1 and hPTTG1 were concordantly upregulated in pituitary (57 and 62%, n=79, P<0.01) and breast tumor specimens (57 and 42%, n=77, P<0.05) respectively. The results show that Oct-1 transactivates hPTTG1, and both proteins are concordantly overexpressed in endocrine tumors, thus offering a mechanism for endocrine tumor hPTTG1 abundance.

Rheumatoid arthritis fibroblast-like synoviocytes express BCMA and are stimulated by APRIL

OBJECTIVE

Fibroblast-like synoviocytes (FLS) are among the principal effector cells in the pathogenesis of rheumatoid arthritis (RA). This study was undertaken to examine the variety of stimulating effects of APRIL and its specific effect on FLS in the affected RA synovium.

METHODS

Synovium and serum samples were obtained from patients with RA, patients with osteoarthritis (OA), and healthy subjects. Soluble APRIL proteins were assayed by enzyme-linked immunosorbent assay. The relative gene expression of APRIL, BCMA, interleukin-6 (IL-6), tumor necrosis factor alpha (TNFalpha), IL-1beta, and RANKL was assessed in RA and OA FLS by polymerase chain reaction. Effects of APRIL on the production of proinflammatory cytokines and RANKL in RA FLS were investigated by flow cytometry and with the use of a BCMA-Fc fusion protein.

RESULTS

A significantly higher level of soluble APRIL was detected in RA serum compared with normal serum. Among the 3 receptors of APRIL tested, RA FLS expressed only BCMA, whereas OA FLS expressed none of the receptors. APRIL stimulated RA FLS, but not OA FLS, to produce IL-6, TNFalpha, IL-1beta, and APRIL itself. In addition, APRIL increased RA FLS expression of RANKL and also enhanced progression of the cell cycle of RA FLS. Neutralization of APRIL by the BCMA-Fc fusion protein attenuated all of these stimulating effects of APRIL on RA FLS.

CONCLUSION

RA FLS are stimulated by APRIL and express the APRIL receptor BCMA. These results provide evidence that APRIL is one of the main regulators in the pathogenesis of RA.

OBF-1 is essential for the generation of antibody-secreting cells and the development of autoimmunity in MRL-lpr mice

As reported previously, the lack of the transcriptional co-activator OBF-1 prevented development of autoimmunity in Aiolos knockout mice. To further investigate the role and mechanism of OBF-1 in autoimmunity, we crossed OBF-1 null mice with MRL-lpr mice and generated OBF-1-deficent MRL-lpr mice. OBF-1 deletion abrogated all autoantibodies in the MRL-lpr mice, including anti-dsDNA Ab and anti-Sm Ab. The failure to produce autoantibodies was not related to development of immature or mature B cells, but correlated with severely reduced antibody-secreting cells (ASCs). The loss of OBF-1 protected against hypergammaglobulinemia, immune complex deposition, glomerulonephritis, and early mortality in MRL-lpr mice. In addition, accumulation of CD4(-)CD8(-)B220(+)CD3(+) T cells that characteristically develop in Fas mutation mice were markedly reduced in MRL-lpr mice without OBF-1. These results identify OBF-1 as a critical gene in the development of autoantibodies and reveal an essential role for OBF-1 in the generation of antibody/autoantibody-secreting cells in vivo.

BOB.1/OBF.1 controls the balance of TH1 and TH2 immune responses

BOB.1/OBF.1 is a transcriptional coactivator essential at several stages of B-cell development. In T cells, BOB.1/OBF.1 expression is inducible by co-stimulation. However, a defined role of BOB.1/OBF.1 for T-cell function had not been discovered so far. Here, we show that BOB.1/OBF.1 is critical for T helper cell function. BOB.1/OBF.1(-/-) mice showed imbalanced immune responses, resulting in increased susceptibility to Leishmania major infection. Functional analyses revealed specific defects in TH1 and TH2 cells. Whereas expression levels of TH1 cytokines were reduced, the secretion of TH2 cytokines was increased. BOB.1/OBF.1 directly contributes to the IFNgamma and IL2 promoter activities. In contrast, increased TH2 cytokine production is controlled indirectly, probably via the transcription factor PU.1, the expression of which is regulated by BOB.1/OBF.1. Thus, BOB.1/OBF.1 regulates the balance of TH1 versus TH2 mediated immunity.

Characterization of an Oct1 orthologue in the channel catfish, Ictalurus punctatus: a negative regulator of immunoglobulin gene transcription?

BACKGROUND

The enhancer (Emu3') of the immunoglobulin heavy chain locus (IGH) of the channel catfish (Ictalurus punctatus) has been well characterized. The functional core region consists of two variant Oct transcription factor binding octamer motifs and one E-protein binding muE5 site. An orthologue to the Oct2 transcription factor has previously been cloned in catfish and is a functionally active transcription factor. This study was undertaken to clone and characterize the Oct1 transcription factor, which has also been shown to be important in driving immunoglobulin gene transcription in mammals.

RESULTS

An orthologue of Oct1, a POU family transcription factor, was cloned from a catfish macrophage cDNA library. The inferred amino acid sequence of the catfish Oct1, when aligned with other vertebrate Oct1 sequences, revealed clear conservation of structure, with the POU specific subdomain of catfish Oct1 showing 96% identity to that of mouse Oct1. Expression of Oct1 was observed in clonal T and B cell lines and in all tissues examined. Catfish Oct1, when transfected into both mammalian (mouse) and catfish B cell lines, unexpectedly failed to drive transcription from three different octamer-containing reporter constructs. These contained a trimer of octamer motifs, a fish VH promoter, and the core region of the catfish Emu3' IGH enhancer, respectively. This failure of catfish Oct1 to drive transcription was not rescued by human BOB.1, a co-activator of Oct transcription factors that stimulates transcription driven by catfish Oct2. When co-transfected with catfish Oct2, Oct1 reduced Oct2 driven transcriptional activation. Electrophoretic mobility shift assays showed that catfish Oct1 (native or expressed in vitro) bound both consensus and variant octamer motifs. Putative N- and C-terminal activation domains of Oct1, when fused to a Gal4 DNA binding domain and co-transfected with Gal4-dependent reporter constructs were transcriptionally inactive, which may be due in part to a lack of residues associated with activation domain function.

CONCLUSION

An orthologue to mammalian Oct1 has been found in the catfish. It is similar to mammalian Oct1 in structure and expression. However, these results indicate that the physiological functions of catfish Oct1 differ from those of mammalian Oct1 and include negative regulation of transcription.

An inducible enhancer required for Il12b promoter activity in an insulated chromatin environment

Interleukin-12 (IL-12) and IL-23 are heterodimeric cytokines that serve as critical regulators of T helper cell development. The Il12b gene, which encodes the p40 subunit of both IL-12 and IL-23, is expressed in macrophages and dendritic cells following induction by bacterial products. Although the Il12b promoter, like the promoters of most proinflammatory genes, can support transcriptional induction in typical transfection assays, we show that it is not sufficient for transcription in an insulated chromatin environment. Using a DNase I hypersensitivity assay, two potential distal control regions were identified. One region, DNase I-hypersensitive site 1 (HSS1), located 10 kb upstream of the transcription start site, exhibited hypersensitivity only in stimulated macrophages. In an insulated environment, a 105-bp fragment spanning HSS1 was sufficient for transcription when combined with the Il12b promoter. Although several elements are likely to contribute to activity of the endogenous HSS1 enhancer, including an evolutionarily conserved binding site for C/EBP proteins, the only element required for activity in transient- and stable-transfection assays bound Oct-1 and Oct-2, both of which are expressed constitutively in macrophages. Oct-1 and Oct-2 were recruited to the enhancer upon macrophage stimulation, and the Oct site appeared important for nucleosome remodeling at HSS1. These results suggest that the HSS1 enhancer and Oct proteins play central roles in Il12b induction upon macrophage activation.

New transcription factors in diagnostic hematopathology

The transcription factors (TFs) that controls the intricate machinery of multistep differentiation and activation programs of the lymphoid system, represent a complex array of proteins, whose identification and function has only in part been completed. TFs are usually expressed during specific differentiation or activation cellular programs, making them interesting tools in diagnostic immunohistochemistry. In fact, the specificity of some of these TFs for lineage or activation/differentiation passages or their abnormal expression in specific disease entity, represents a feature that has been exploited in diagnostic/prognostic immunohistochemistry. Bcl-6 was the prototype of this class of markers. Currently, the expanding knowledge of the TFs involved in the differentiation programs and in the activation processes of T-lymphocyte and B-lymphocyte in normal and neoplastic conditions and the availability of antibodies able to efficiently recognize these TFs in histologic material, represent a powerful tool in diagnostic hematopathology. In this review we will consider the basic biologic aspects and the applications in hematopathology of some of the lymphocyte-related TFs, including Pax5/BSAB, MUM1/IRF4, BOB1, Oct-2, T-bet, and FOXP3. This field is rapidly evolving, as witnessed by the ongoing growing number of novel TFs with possible diagnostic applications appearing in the literature.

Regulation of NF-kappaB-dependent gene expression by the POU domain transcription factor Oct-1

Maintenance of the cells of the vessel wall in a quiescent state is an important aspect of normal vascular physiology. Transcriptional repressors are widely believed to regulate this process, yet the exact factors involved and the mechanism of repression are not known. Here, we report that the POU domain transcription factor Oct-1 represses the expression of E-selectin and vascular cell adhesion molecule (VCAM-1), two cytokine-inducible, NF-kappaB-dependent endothelial-leukocyte adhesion molecules that participate in the leukocyte recruitment phase of the inflammatory response. Co-transfection and microinjection studies demonstrate that Oct-1 blocks tumor necrosis factor alpha-stimulated E-selectin and VCAM-1 expression. Gene expression arrays indicate that control of tumor necrosis factor alpha-induced, NF-kappaB-dependent gene expression by Oct-1 is promoter-specific. A DNA-binding mutant of Oct-1 represses NF-kappaB-dependent reporter gene expression. Biochemically, Oct-1 interacts with p65, suggesting that Oct-1 is involved in the regulation of NF-kappaB transactivation function. NF-kappaB-dependent gene expression is more pronounced in Oct-1-deficient than in wild-type murine embryonic fibroblasts, and reintroduction of human Oct-1 abolishes these differences. Finally, the cytokine interleukin-6 induces Oct-1 gene expression, providing a biologically relevant means by which NF-kappaB-dependent gene expression can be selectively reverted by Oct-1 to quiescent levels.

B29 gene silencing in pituitary cells is regulated by its 3' enhancer

B cell-specific B29 (Igbeta, CD79b) genes in rat, mouse, and human are situated between the 5' growth hormone (GH) locus control region and the 3' GH gene cluster. The entire GH genomic region is DNase 1 hypersensitive in GH-expressing pituitary cells, which predicts an "open" chromatin configuration, and yet B29 is not expressed. The B29 promoter and enhancers exhibit histone deacetylation in pituitary cells, but histone deacetylase inhibition failed to activate B29 expression. The B29 promoter and a 3' enhancer showed local dense DNA methylation in both pituitary and non-lymphoid cells consistent with gene silencing. However, DNA methyltransferase inhibition did not activate B29 expression either. B29 promoter constructs were minimally activated in transfected pituitary cells. Co-transfection of the B cell-specific octamer transcriptional co-activator Bob1 with the B29 promoter construct resulted in high level promoter activity in pituitary cells comparable to B29 promoter activity in transfected B cells. Unexpectedly, inclusion of the B29 3' enhancer in B29 promoter constructs strongly inhibited B29 transcriptional activity even when pituitary cells were co-transfected with Bob1. Both Oct-1 and Pit-1 bind the B29 3' enhancer in in vitro electrophoretic mobility shift assay and in in vivo chromatin immunoprecipitation analyses. These data indicate that the GH locus-embedded, tissue-specific B29 gene is silenced in GH-expressing pituitary cells by epigenetic mechanisms, the lack of a B cell-specific transcription factor, and likely by the B29 3' enhancer acting as a powerful silencer in a context and tissue-specific manner.

Rap1 signal controls B cell receptor repertoire and generation of self-reactive B1a cells

We previously reported that the mice deficient for SPA-1, a Rap1 GTPase-activating protein, developed hematopoietic stem cell disorders. Here, we demonstrate that SPA-1(-/-) mice show an age-dependent increase in B220(high) B1a cells producing anti-dsDNA antibody and lupus-like nephritis. SPA-1(-/-) peritoneal B1 cells revealed the altered Vkappa gene repertoire, including skewed Vkappa4 usage and the significant Igkappa/Iglambda isotype inclusion indicative of extensive receptor editing. Rap1GTP induced OcaB gene activation via p38MAPK-dependent Creb phosphorylation, and consistently, SPA-1(-/-) immature BM B cells showing high Rap1GTP exhibited the augmented expression of OcaB and Vkappa4 genes. SPA-1(-/-) BM cells could transfer the autoimmunity in association with the generation of peritoneal B220(high) B1a cells in Rag-2(-/-) recipients. Finally, a portion of SPA-1(-/-) mice developed B1 cell leukemia with hemolytic autoantibody. Present results suggest that the regulated Rap1 signal in the immature B cells plays a role in modifying the B cell receptor repertoire and in maintaining the self-tolerance.

Btk expression is controlled by Oct and BOB.1/OBF.1

BOB.1/OBF.1 is a lymphocyte-restricted transcriptional coactivator. It binds together with the Oct1 and Oct2 transcription factors to DNA and enhances their transactivation potential. Mice deficient for the transcriptional coactivator BOB.1/OBF.1 show several defects in differentiation, function and signaling of B cells. In search of BOB.1/OBF.1 regulated genes we identified Btk—a cytoplasmic tyrosine kinase—as a direct target of BOB.1/OBF.1. Analyses of the human as well as murine Btk promoters revealed a non-consensus octamer site close to the start site of transcription. Here we show that Oct proteins together with BOB.1/OBF.1 are able to form ternary complexes on these sites in vitro and in vivo. This in turn leads to the induction of Btk promoter activity in synergism with the transcription factor PU.1. Btk, like BOB.1/OBF.1, plays a critical role in B cell development and B cell receptor signalling. Therefore the down-regulation of Btk expression in BOB.1/OBF.1-deficient B cells could be related to the functional and developmental defects observed in BOB.1/OBF.1-deficient mice.

Oct2 transcription factors in fish--a comparative genomic analysis

The Oct2 transcription factor is important in driving expression of the IgH locus of the channel catfish, Ictalurus punctatus. Two isoforms, catfish Oct2alpha and Oct2beta, have been characterized at the level of expression and function, but little is known of the structure of the Oct2 gene in catfish. To gain insight into the diversity of Oct2 gene structure and expression in the teleost fish, a comparative genomic analysis of Oct2 was undertaken in the pufferfish (Fugu rubripes) and the zebrafish (Danio rerio). The orthologues of zebrafish and Fugu Oct2 were identified, and share with catfish Oct2 the expression of a limited number (two in zebrafish, three in Fugu) of isotypes produced by alternative pathways of RNA processing. The alternatively spliced variants of catfish Oct2 showed a different pattern of exon use from those of Fugu and zebrafish. The analysis also identified a novel homologue of Oct2 in both zebrafish and Fugu. This homologue, termed Oct2x, shares similarities to both Oct1 and Oct2. A phylogenetic analysis of the relationships of Oct2x gave an unexpected result, with Oct2x occupying a position basal to the Oct gene families of both vertebrates and Drosophila.

RNA Stability of the E2A-Encoded Transcription Factor E47 Is Lower in Splenic Activated B Cells from Aged Mice

We have demonstrated previously that DNA binding and protein expression of the E2A-encoded transcription factor E47 are lower in nuclear extracts of activated splenic B cells from old mice. In the present study, we address how E47 protein expression is regulated in aging. Results herein show that E2A mRNA levels were decreased in stimulated splenic B cells from old as compared with young mice. RNA stability assays showed that the rate of E2A mRNA decay was accelerated in stimulated splenic B cells from old mice, but E47 protein degradation rates were comparable in young vs aged B cells, indicating that the regulation of E47 expression in activated splenic B cells occurs primarily by mRNA stability. The rates of decay of other mRNAs showed that the increased mRNA degradation in aged splenic activated B cells is not a general phenomenon but restricted to a subset of mRNAs. We next investigated the signal transduction pathways controlling E2A mRNA expression and stability and found that p38 MAPK regulates E2A mRNA expression through increased mRNA stability and is down-regulated in aged activated B cells. Results show that inhibition of p38 MAPK significantly reduces E2A mRNA stability in both young and old B cells, further stressing the role of p38 MAPK in E2A RNA stabilization. These studies demonstrate that the transcription factor E2A, critical for many aspects of B cell function, is regulated by a novel mechanism in aging.

Use of altered-specificity binding Oct-4 suggests an absence of pluripotent cell-specific cofactor usage

Oct-4 is a POU domain transcription factor that is critical for maintaining pluripotency and for stem cell renewal. Previous studies suggest that transcription regulation by Oct-4 at particular enhancers requires the input of a postulated E1A-like cofactor that is specific to pluripotent cells. However, such studies have been limited to the use of enhancer elements that bind other POU-protein family members in addition to Oct-4, thus preventing a ‘clean’ assessment of any Oct-4:cofactor relationships. Other attempts to study Oct-4 functionality in a more ‘stand-alone’ situation target Oct-4 transactivation domains to DNA using heterologous binding domains, a methodology which is known to generate artificial data. To circumvent these issues, an altered-specificity binding Oct-4 (Oct-4RR) and accompanying binding site, which binds Oct-4RR only, were generated. This strategy has previously been shown to maintain Oct-1:cofactor interactions that are highly binding-site and protein/binding conformation specific. This system therefore allows a stand-alone study of Oct-4 function in pluripotent versus differentiated cells, without interference from endogenous POU factors and with minimal deviation from bound wild-type protein characteristics. Subsequently, it was demonstrated that Oct-4RR and the highly transactive regions of its N-terminus determined here, and its C-terminus, have the same transactivation profile in pluripotent and differentiated cells, thus providing strong evidence against the existence of such a pluripotent cell-specific Oct-4 cofactor.

Transcriptional control of B cell activation

The developmental program that commits a hematopoietic stem cell to the B lymphocyte lineage employs transcriptional regulators to enable the assembly of an antigen receptor complex with a useful specificity and with signalling competence. Once a naive IgM+ B cell is generated, it must correctly integrate signals from the antigen receptor with those from cytokine receptors and co-receptors delivering T cell help. The B cell responds through the regulated expression of genes that implement specific cell expansion and differentiation, secretion of high levels of high-affinity antibody, and generation of long-term memory. The transcriptional regulators highlighted in this chapter are those for which genetic evidence of function in IgM+ B cells in vivo has been provided, often in the form of mutant mice generated by conventional or conditional gene targeting. A critical developmental step is the maturation of bone marrow emigrant "transitional" B cells into the mature, long-lived cells of the periphery, and a number of the transcription factors discussed here impact on this process, yielding B cells with poor mitogenic responses in vitro. For mature B cells, it is clear that not only the nature, but the duration and amplitude of an activating signal are major determinants of the transcription factor activities enlisted, and so the ultimate outcome. The current challenge is the identification of the target genes that are activated to implement the correct response, so that we may more precisely and safely manipulate B cell behavior to predictably and positively influence humoral immune responses.

Differential requirement for OBF-1 during antibody-secreting cell differentiation

Resting B cells can be cultured to induce antibody-secreting cell (ASC) differentiation in vitro. A quantitative analysis of cell behavior during such a culture allows the influences of different stimuli and gene products to be measured. The application of this analytical system revealed that the OBF-1 transcriptional coactivator, whose loss impairs antibody production in vivo, has two effects on ASC development. Although OBF-1 represses early T cell–dependent (TD) differentiation, it is also critical for the completion of the final stages of ASC development. Under these conditions, the loss of OBF-1 blocks the genetic program of ASC differentiation so that Blimp-1/prdm1 induction fails, and bcl-6, Pax5, and AID are not repressed as in control ASC. Retroviral complementation confirmed that OBF-1 was the critical entity. Surprisingly, when cells were cultured in lipopolysaccharide to mimic T cell–independent conditions, OBF-1–null B cells differentiated normally to ASC. In the OBF-1^−/− ASC generated under either culture regimen, antibody production was normal or only modestly reduced, revealing that Ig genes are not directly dependent on OBF-1 for their expression. The differential requirement for OBF-1 in TD ASC generation was confirmed in vivo. These studies define a new regulatory role for OBF-1 in determining the cell-autonomous capacity of B cells to undergo terminal differentiation in response to different immunological signals.

Identification of a potential role for POU2AF1 and BTG4 in the deletion of 11q23 in chronic lymphocytic leukemia

Deletions of 11q in chronic lymphocytic leukemia (CLL) are usually associated with progressive disease and poor prognosis. A novel translocation within the previously identified 11q minimal region has been defined in a patient with CLL. The breakpoint is between genes POU2AF1 and BTG4. POU2AF1 is a B-cell-specific transcriptional coactivator, and BTG4 is a member of the BTG family of negative regulators of the cell cycle, making both of them good candidate genes for the pathogenesis of 11q- CLL. POU2AF1 was observed to be differentially expressed in the cells of patients with CLL compared to its expression in normal B cells in the absence of mutations. This may reflect ongoing stimulation and active accessory signaling in CLL cells. BTG4 could contribute to CLL pathogenesis following inactivation by haploinsufficiency.

Transcription factor Sox-2 inhibits co-activator stimulated transcription

Previous studies have shown that transcription of the fibroblast growth factor-4 (FGF-4) gene by early embryonic cells is dependent upon a powerful distal enhancer located 3 kb downstream of the transcription start site within the untranslated region of the last exon. The transcription factors Sox-2 and Oct-3 cooperatively bind to critical cis-regulatory elements within the enhancer to synergistically activate transcription. Moreover, the co-activator p300 can mediate the synergistic activity of Sox-2 and Oct-3, and p300 associates with the FGF-4 enhancer in vivo. Embryonal carcinoma (EC) cells have been used extensively as a model system to study the regulation of the FGF-4 gene during early development. Recently, it has been suggested that suboptimal levels of Sox-2 expression in F9 EC cells limit the transcription of the FGF-4 gene. The studies presented in this report argue that Sox-2 levels are not limiting in F9 EC cells. Moreover, overexpression of Sox-2 in F9 EC cells decreases FGF-4 promoter activity. In addition, overexpression of Sox-2 in these cells inhibits activation by the co-activators p300, CBP, and OCA-B in a manner that requires the transactivation domain of Sox-2. These findings suggest that Sox-2 levels in F9 EC cells are regulated carefully to avoid interference with the transcription of critical genes.

RAGs and regulation of autoantibodies

Autoreactive antibodies are etiologic agents in a number of autoimmune diseases. Like all other antibodies these antibodies are produced in developing B cells by V(D)J recombination in the bone marrow. Three mechanisms regulate autoreactive B cells: deletion, receptor editing, and anergy. Here we review the prevalence of autoantibodies in the initial antibody repertoire, their regulation by receptor editing, and the role of the recombinase proteins (RAG1 and RAG2) in this process.

TALE homeodomain proteins regulate gonadotropin-releasing hormone gene expression independently and via interactions with Oct-1

Gonadotropin-releasing hormone (GnRH) is the central regulator of reproductive function. Expression of the GnRH gene is confined to a rare population of neurons scattered throughout the hypothalamus. Restricted expression of the rat GnRH gene is driven by a multicomponent enhancer and an evolutionarily conserved promoter. Oct-1, a ubiquitous POU homeodomain transcription factor, was identified as an essential factor regulating GnRH transcription in the GT1-7 hypothalamic neuronal cell line. In this study, we conducted a two-hybrid interaction screen in yeast using a GT1-7 cDNA library to search for specific Oct-1 cofactors. Using this approach, we isolated Pbx1b, a TALE homeodomain transcription factor that specifically associates with Oct-1. We show that heterodimers containing Pbx/Prep1 or Pbx/Meis1 TALE homeodomain proteins bind to four functional elements within the GnRH regulatory region, each in close proximity to an Oct-1-binding site. Cotransfection experiments indicate that TALE proteins are essential for GnRH promoter activity in the GT1-7 cells. Moreover, Pbx1 and Oct-1, as well as Prep1 and Oct-1, form functional complexes that enhance GnRH gene expression. Finally, Pbx1 is expressed in GnRH neurons in embryonic as well as mature mice, suggesting that the associations between TALE homeodomain proteins and Oct-1 regulate neuron-specific expression of the GnRH gene in vivo.

Cloning, genomic organization, expression, and effect on beta-casein promoter activity of a novel isoform of the mouse Oct-1 transcription factor

The ubiquitously expressed transcription factor Oct-1, a member of the POU domain factors, is involved in the regulation of expression of many tissue-specific and house-keeping genes. Multiple alternatively spliced isoforms of Oct-1 have been identified in human and mouse cells. The expression patterns of these isoforms and the analysis of their genomic organization and structure have suggested that the structural variation of Oct-1 isoforms may be important in conferring target and tissue specificity to its transcriptional activity. In this study, we have cloned and sequenced a new mouse Oct-1 isoform, named mOct-1Z. This novel isoform differs markedly at the C-terminus from the previously identified Oct-1 isoforms A, B, and C. It is generated by alternative splicing from the Oct-1 gene and its transcript exhibits a frameshift followed by an early stop codon, thus, its predicted protein has a distinct, much shorter C-terminal tail. However, this truncated isoform could still effectively bind to a consensus Oct-1 motif oligonucleotide and, like Oct-1B, activated the basal promoter activity of the mouse beta-casein gene. Oct-1Z is another ubiquitously expressed Oct-1 isoform, its transcript being detected in all mouse tissues examined, including the mammary gland, liver, lung, kidney, spleen, small intestine mucosa, uterus, and ovary.

Myosin light chain 1 atrial isoform (MLC1A) is expressed in pre-B cells under control of the BOB.1/OBF.1 coactivator

The BOB.1/OBF.1 protein is a B-cell-specific coactivator of the Oct1 and Oct2 transcription factors. It is involved in mediating the transcriptional activity of the Oct proteins. However, animals deficient for BOB.1/OBF.1 showed virtually normal expression of genes that contain octamer motifs in their regulatory regions. To identify new genes that are regulated by BOB.1/OBF.1, we took advantage of a previously described cell system. RNAs differentially expressed in a BOB.1/OBF.1-deficient pre-B cell line and a derivative of this cell line expressing a hormone dependent BOB.1/OBF.1-estrogen receptor (BobER) fusion protein were isolated. Using the cDNA representational difference analysis method we could identify myosin light chain 1 atrial (MLC1A) isoform as a gene regulated by BOB.1/OBF.1. MLC1A was so far unknown to be expressed in tissues other than muscle. Here we demonstrate that MLC1A is indeed expressed in mouse pre-B cells. Analysis of the expressed mRNA revealed an alternative 5' promoter element and an alternative splice product, which had not yet been described for the murine gene. Cotransfection experiments with reporter constructs driven by the MLC1A promoter suggest that the regulation by BOB.1/OBF.1 is indirect. Consistent with this conclusion is the observation that transcriptional induction of the endogenous MLC1A gene by BOB.1/OBF.1 requires de novo protein synthesis.