OCA-B/Pou2af1 is sufficient to promote CD4+ T cell memory and prospectively identifies memory precursors.

The molecular mechanisms leading to the establishment of immunological memory are inadequately understood, limiting the development of effective vaccines and durable antitumor immune therapies. Here, we show that ectopic OCA-B expression is sufficient to improve antiviral memory recall responses, while having minimal effects on primary effector responses. At peak viral response, short-lived effector T cell populations are expanded but show increased Gadd45b and Socs2 expression, while memory precursor effector cells show increased expression of Bcl2, Il7r, and Tcf7 on a per-cell basis. Using an OCA-B mCherry reporter mouse line, we observe high OCA-B expression in CD4+ central memory T cells. We show that early in viral infection, endogenously elevated OCA-B expression prospectively identifies memory precursor cells with increased survival capability and memory recall potential. Cumulatively, the results demonstrate that OCA-B is both necessary and sufficient to promote CD4 T cell memory in vivo and can be used to prospectively identify memory precursor cells.

IκBζ is a dual-use coactivator of NF-κB and POU transcription factors.

OCA-B, OCA-T1, and OCA-T2 belong to a family of coactivators that bind to POU transcription factors (TFs) to regulate gene expression in immune cells. Here, we identify IκBζ (encoded by the NFKBIZ gene) as an additional coactivator of POU TFs. Although originally discovered as an inducible regulator of NF-κB, we show here that IκBζ shares a microhomology with OCA proteins and uses this segment to bind to POU TFs and octamer-motif-containing DNA. Our functional experiments suggest that IκBζ requires its interaction with POU TFs to coactivate immune-related genes. This finding is reinforced by epigenomic analysis of MYD88L265P-mutant lymphoma cells, which revealed colocalization of IκBζ with the POU TF OCT2 and NF-κB:p50 at hundreds of DNA elements harboring octamer and κB motifs. These results suggest that IκBζ is a transcriptional coactivator that can amplify and integrate the output of NF-κB and POU TFs at inducible genes in immune cells.

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.

OCA-B does not act as a transcriptional coactivator in T cells.

Pou2af1 encodes for OCA-B, a coactivator of OCT-1/2 transcription factors, which plays a key role in B-cell maturation. The function of OCA-B has also been studied in T cells, where T cells from Pou2af1-/- mice have impaired functions, such as cytokine production and T follicular helper (Tfh) differentiation. Arguably, some of these T-cell phenotypes may result from impaired T-B interactions, secondary to the well-documented B-cell defects in Pou2af1-/- mice. Yet, Pou2af1 is actively transcribed in activated T cells, suggesting a T-cell-intrinsic role. To isolate the T-cell-intrinsic impact of Pou2af1, we generated Pou2af1fl/fl mice with specific genetic disruption of Pou2af1 either in all hematopoietic cells or exclusively in T cells. While we confirm that Pou2af1 is expressed in activated T cells, we surprisingly find that T-cell cytokine production is not impaired in Pou2af1-deficient T cells. Moreover, Pou2af1-sufficient and Pou2af1-deficient T cells have comparable transcriptome profiles, arguing against a T-cell-intrinsic role for Pou2af1. In line with these observations, we demonstrate that Tfh maturation is influenced by T-cell-extrinsic deletion of Pou2af1, as observed both in competitive bone marrow chimeras and in Pou2af1fl/fl mice with specific deletion in B cells. Overall, this study provides strong evidence that Pou2af1 does not act as a transcriptional coactivator in T cells, and conclusively demonstrates that loss of OCA-B in B cells indirectly impacts Tfh differentiation, clarifying the role of OCA-B in the immune system.

Unique Immune Cell Coactivators Specify Locus Control Region Function and Cell Stage.

Locus control region (LCR) functions define cellular identity and have critical roles in diseases such as cancer, although the hierarchy of structural components and associated factors that drive functionality are incompletely understood. Here we show that OCA-B, a B cell-specific coactivator essential for germinal center (GC) formation, forms a ternary complex with the lymphoid-enriched OCT2 and GC-specific MEF2B transcription factors and that this complex occupies and activates an LCR that regulates the BCL6 proto-oncogene and is uniquely required by normal and malignant GC B cells. Mechanistically, through OCA-B-MED1 interactions, this complex is required for Mediator association with the BCL6 promoter. Densely tiled CRISPRi screening indicates that only LCR segments heavily bound by this ternary complex are essential for its function. Our results demonstrate how an intimately linked complex of lineage- and stage-specific factors converges on specific and highly essential enhancer elements to drive the function of a cell-type-defining LCR.

MTA2/NuRD Regulates B Cell Development and Cooperates with OCA-B in Controlling the Pre-B to Immature B Cell Transition.

The NuRD complex contains both chromatin remodeling and histone deacetylase activities. Mice lacking the MTA2 subunit of NuRD show developmental defects in pro-B, pre-B, immature B, and marginal zone B cells, and abnormal germinal center B cell differentiation during immune responses. Mta2 inactivation also causes a derepression of Igll1 and VpreB1 genes in pre-B cells. Furthermore, MTA2/NuRD interacts directly with AIOLOS/IKAROS and shows a striking overlap with AIOLOS/IKAROS target genes in human pre-B cells, suggesting a functional inter-dependence between MTA2/NuRD and AIOLOS. Mechanistically, MTA2 deficiency in mice leads to increased H3K27 acetylation at both Igll1 and VpreB1 promoters. Gene profiling analyses also identify distinct MTA2-dependent transcription programs in pro-B and pre-B cells. In addition, we find a strong synergy between MTA2 and OCA-B in repressing Igll1 and VpreB1 at the pre-B cell stage, and in regulating both the pre-B to immature B transition and splenic B cell development.

Role of OCT-1 and partner proteins in T cell differentiation.

The understanding of CD4 T cell differentiation gives important insights into the control of immune responses against various pathogens and in autoimmune diseases. Naïve CD4 T cells become effector T cells in response to antigen stimulation in combination with various environmental cytokine stimuli. Several transcription factors and cis-regulatory regions have been identified to regulate epigenetic processes on chromatin, to allow the production of proper effector cytokines during CD4 T cell differentiation. OCT-1 (Pou2f1) is well known as a widely expressed transcription factor in most tissues and cells. Although the importance of OCT-1 has been emphasized during development and differentiation, its detailed molecular underpinning and precise role are poorly understood. Recently, a series of studies have reported that OCT-1 plays a critical role in CD4 T cells through regulating gene expression during differentiation and mediating long-range chromosomal interactions. In this review, we will describe the role of OCT-1 in CD4 T cell differentiation and discuss how this factor orchestrates the fate and function of CD4 effector T cells.