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The basic leucine zipper family (bZIP) represents one of the largest families of transcription factors that play an important role in plant responses to abiotic stresses. However, their role in contributing to thermotolerance in plants is not well explored. In this article, two homoeologs of wheat ocs-element binding factor 1 (TaOBF1-5B and TaOBF1-5D) were found to be heat-responsive TabZIP members. Their expression analysis in Indian wheat cultivars revealed their differential expression pattern and TaOBF1-5B was found to be more receptive to heat stress. Consistent with this, the heterologous overexpression of TaOBF1-5B in Arabidopsis thaliana and Oryza sativa promoted the expression of stress-responsive genes, which contributed to thermotolerance in transgenic plants. TaOBF1-5B was seen to interact with TaHSP90 in the nucleus and TaSTI in the nucleolus and the ER. Thus, the results suggest that TaOBF1-5B might play an important regulatory role in the heat stress response and is a major factor governing thermotolerance in plants.

The Oct2 protein, encoded by the Pou2f2 gene, was originally predicted to act as a DNA binding transcriptional activator of immunoglobulin (Ig) in B lineage cells. This prediction flowed from the earlier observation that an 8-bp sequence, the \"octamer motif,\" was a highly conserved component of most Ig gene promoters and enhancers, and evidence from over-expression and reporter assays confirmed Oct2-mediated, octamer-dependent gene expression. Complexity was added to the story when Oct1, an independently encoded protein, ubiquitously expressed from the Pou2f1 gene, was characterized and found to bind to the octamer motif with almost identical specificity, and later, when the co-activator Obf1 (OCA-B, Bob.1), encoded by the Pou2af1 gene, was cloned. Obf1 joins Oct2 (and Oct1) on the DNA of a subset of octamer motifs to enhance their transactivation strength. While these proteins variously carried the mantle of determinants of Ig gene expression in B cells for many years, such a role has not been borne out for them by characterization of mice lacking functional copies of the genes, either as single or as compound mutants. Instead, we and others have shown that Oct2 and Obf1 are required for B cells to mature fully in vivo, for B cells to respond to the T cell cytokines IL5 and IL4, and for B cells to produce IL6 normally during a T cell dependent immune response. We show here that Oct2 affects Syk gene expression, thus influencing B cell receptor signaling, and that Oct2 loss blocks Slamf1 expression in vivo as a result of incomplete B cell maturation. Upon IL4 signaling, Stat6 up-regulates Obf1, indirectly via Xbp1, to enable plasma cell differentiation. Thus, Oct2 and Obf1 enable B cells to respond normally to antigen receptor signals, to express surface receptors that mediate physical interaction with T cells, or to produce and respond to cytokines that are critical drivers of B cell and T cell differentiation during a humoral immune response.

Autoimmune diseases, despite the significant work that has been carried out in biomedicine for several decades, continue to be largely incurable and poorly understood in terms of the molecular mechanisms of their occurrence and development. It is generally accepted that these diseases, whose main attributes are autoreactive B- and T-lymphocytes, are caused by a malfunction of the adaptive immune system. Extensive experimental data accumulated over the past few years indicate the key role of the transcriptional coactivator BOB1 in the emergence of autoreactive lymphocytes. It has been postulated that BOB1 affects transcription and the local epigenetic status of chromatin indirectly, namely, through selective interaction with DNA-binding POU-domain transcription factors, with OCT1 expressing in all cells, as well as OCT2, which is specific to B cells, stabilizing the binding of these OCT factors to DNA. The review provides the latest information on the pro-autoimmune activity of BOB1 and outlines the prospects for the application of this protein as a target in the development of pharmaceuticals aimed at treating a number of autoimmune diseases.

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.

Mice homozygous for a point mutation in the Rc3h1 gene encoding Roquin1, designated sanroque mice, develop a severe antibody‐mediated autoimmune condition. The disease is T‐cell intrinsic, exacerbated by macrophage‐intrinsic defects and driven by excessive T follicular helper cell generation and spontaneous germinal centre (GC) formation. This culminates in abnormally high numbers of plasma cells secreting high‐affinity autoreactive immunoglobulin G (IgG). Obf1 is a transcriptional co‐activator required for normal T‐cell‐dependent antibody responses, and it is essential for GC formation under all circumstances so far tested. We crossed sanroque mice with Obf1‐null mice to determine whether the hyperactivity of sanroque T cells could drive Obf1−/− B cells to differentiate to GC B cells, or conversely, if Obf1 loss would prevent sanroque‐mediated autoimmune disease. Surprisingly, while sanroque/Obf1−/− mice did not form GC, they still developed autoimmune disease and succumbed even more rapidly than did sanroque mice. The disease was mediated by autoreactive IgM, which may have been derived from a pre‐existing population of autoreactive B cells in the Obf1−/− mice responding to the over‐exuberant activity of sanroque CD4 cells.

The POU transcription factors Oct1 and Oct2 bind to DNA in various monomer and dimer configurations. Depending on the DNA sequence to which they bind, the dimers are arranged in configurations that are either accessible (PORE sequence) or inaccessible (MORE sequence) to the B‐cell‐specific cofactor OBF1 (OcaB, Bob1). As shown previously, the MORE and related sequences (such as the heptamer/octamer motif) are found in immunoglobulin heavy chain promoters. Here we show that the expression of Osteopontin , which contains a PORE sequence in its enhancer region, depends on the presence of OBF1 in B cells. OBF1 alleviates DNA sequence requirements of the Oct1 dimer on PORE‐related sequences in vitro . Furthermore, OBF1 stabilizes POU dimer–DNA interactions and overrides Oct1 interface mutations, which abolish PORE‐mediated dimerization without OBF1. Our data indicate that the PORE‐type Oct1 or Oct2 dimer, rather than the monomer, is the primary target of the cofactor OBF1. Based on our biochemical data, we propose a mode of OBF1–Oct1 dimer interaction, suggesting a novel arrangement of the subdomain connectivities.

The World Health Organization (WHO) classification of Hodgkin lymphoma (HL) distinguishes two types: Classical Hodgkin lymphoma (CHL) and nodular lymphocyte predominant Hodgkin lymphoma (NLPHL). Both groups have in common that they mostly derive from B cells with rare classical cases originating from T cells. They differ in their histomorphology, immunophenotype, and clinical behavior. One of the subtypes of CHL, designated as lymphocyte-rich classical Hodgkin lymphoma (LRCHL), shares some morphological features with NLPHL. The transcription factors BSAP, BOB.1, Oct2 and MUM1 are sequentially expressed in normal B-cell development. In order to investigate the relationship between the CHL subgroups and NLPHL, we examined the protein expression of these transcription factors using immunohistochemistry in 15 reactive processes and 4 different subtypes of 58 HL cases. Our findings underline the B-cell origin of HL, without evidence, that reactive processes like progressively transformed germinal centers (PTGCs) are precursor lesions of HL. Furthermore, they demonstrate that LRCHL is distinct from NLPHL and that it is closely related to the mixed cellularity CHL (MCHL) in respect of BSAP, BOB.1, and Oct2 expression. It therefore occupies an intermediate position between MCHL and NLPHL. Based on MUM1 staining, LRCHL exhibits a more mature phenotype than NLPHL.

We have dissected the autonomously replicating sequence ARS121 using site-directed in vitro mutagenesis. Three domains important for origin function were identified; one of these is essential and contains an 11-base-pair sequence resembling the canonical ARS core consensus; the second region, deletion of which affects the efficiency of the origin, is located 3' to the T-rich strand of the essential sequence and encompasses several elements with near matches to the ARS core consensus; the third region, containing two OBF1 DNA-binding sites and located 5' to the essential sequence, also affects the efficiency of the ARS. Here we demonstrate that a synthetic OBF1 DNA-binding site can substitute for the entire third domain in origin function. A dimer of the synthetic binding site, fused to a truncated origin containing only domains one and two, restored the origin activity to the levels of the wild-type ARS. The stimulation of origin function by the synthetic binding site was relatively orientation independent and could occur at distances as far as 1 kilobase upstream to the essential domain. Based on these results we conclude that the OBF1 DNA-binding site is an enhancer of DNA replication. We suggest that the DNA-binding site and the OBF1 protein are involved in the regulation of the activation of nuclear origins of replication in Saccharomyces cerevisiae.