The small FOXP1 isoform predominantly expressed in activated B cell-like diffuse large B-cell lymphoma and full-length FOXP1 exert similar oncogenic and transcriptional activity in human B cells

SRSF4-Associated ca-circFOXP1 Regulates Hypoxia-Induced PASMC Proliferation by the Formation of R Loop With Host Gene

BACKGROUND

Pulmonary hypertension (PH) is a rare and fatal disease, the pathological changes of which include pulmonary arterial smooth muscle cell (PASMC) proliferation, which is the pathological basis of pulmonary vascular remodeling. Studies have demonstrated that chromatin-associated circRNA can regulate a variety of biological processes. However, the role of chromatin-associated circRNA in the proliferation of PH remains largely unexplored. In this study, we aimed to identify the function and mechanism of chromatin-associated circRNA in PASMC proliferation in PH.

METHODS

The role of chromatin-associated circFOXP1 (ca-circFOXP1) was investigated in hypoxic mouse PASMCs and SuHX (Sugen5416+hypoxia) model mice through the use of antisense oligonucleotide knockdown and adeno-associated virus-mediated knockdown. Through bioinformatic sequence alignment, chromatin isolation by RNA purification, Cell Counting Kit 8, 5-ethynyl-2-deoxyuridine, Western blot, and other experiments, the function and mechanism of ca-circFOXP1 were verified.

RESULTS

The expression of ca-circFOXP1 was found to be significantly increased in SuHX model mice and hypoxic mouse PASMCs. Moreover, ca-circFOXP1 was found to regulate the level of the host protein FOXP1 (forkhead box protein 1) through the R loop, thereby influencing the phosphorylation activity of SMAD2 (SMAD family member 2) and, consequently, the proliferation of mouse PASMCs. It is noteworthy that the m6A modification was found to promote the formation of the R loop between ca-circFOXP1 and the host gene FOXP1, thereby regulating the expression of the host protein. Furthermore, we have identified that the splicing factor SRSF4 (serine/arginine rich splicing factor 4) can upregulate the expression of ca-circFOXP1 by splicing exons 6 and 9 of FOXP1 pre-mRNA.

CONCLUSIONS

The results demonstrated that the splicing factor SRSF4 upregulated the expression of ca-circFOXP1, and m6A methylation promoted R-loop formation between ca-circFOXP1 and host genes, regulated the level of host protein FOXP1, and then affected the phosphorylation activity of SMAD2, mediating PASMC proliferation, leading to pulmonary vascular remodeling. These results provide a theoretical basis for further study of the pathological mechanisms of hypoxic PH and may provide certain insights.

DNA damage-induced p53 downregulates expression of RAG1 through a negative feedback loop involving miR-34a and FOXP1

During the maturation of pre-B cells, the recombination activating gene 1 and 2 (RAG1/2) endonuclease complex plays a crucial role in coordinating V(D)J recombination by introducing DNA breaks in immunoglobulin (Ig) loci. Dysregulation of RAG1/2 has been linked to the onset of B cell malignancies, yet the mechanisms controlling RAG1/2 in pre-B cells exposed to excessive DNA damage are not fully understood. In this study, we show that DNA damage-induced activation of p53 initiates a negative-feedback loop which rapidly downregulates RAG1 levels. This feedback loop involves ataxia telangiectasia mutated activation, subsequent stabilization of p53, and modulation of microRNA-34a (miR-34a) levels, which is one of the p53 targets. Notably, this loop incorporates transcription factor forkhead box P1 as a downstream effector. The absence of p53 resulted in an increased proportion of IgM+ cells prompted to upregulate RAG1/2 and to undergo Ig light chain recombination. Similar results were obtained in primary pre-B cells with depleted levels of miR-34a. We propose that in pre-B cells undergoing Ig gene recombination, the DNA breaks activate a p53/miR-34a/forkhead box P1-mediated negative-feedback loop that contributes to the rapid downregulation of RAG. This regulation limits the RAG-dependent DNA damage, thereby protecting the stability of the genome during V(D)J rearrangement in developing B cells.

miR-34a-FOXP1 Loop in Ovarian Cancer

Ovarian cancer (OC) is the main cause of gynecological cancer mortality in most developed countries. microRNA (miR) expression dysregulation has been highlighted in human cancers, and miR-34a is found to be downregulated and associated with inhibition of tumor growth and invasion in several malignancies, including OC. The winged helix transcription factor forkhead box P1 (FOXP1) is reported as either an oncogene or tumor suppressor in various cancers. This study aimed to elucidate potential clinical and biological associations of miR-34a and transcription factor FOXP1 in OC. We investigated nine OC patients' blood samples and two OC cell lines (SKOV-3 and OVCAR-3) using quantitative real-time reverse transcription polymerase chain reaction (RT-qPCR) to determine both miR-34a and FOXP1 expressions. We have found that miR-34a and FOXP1 are reversely correlated in both in vitro and in vivo. Inhibition of miR-34a transiently led to upregulation of FOXP1 mRNA expression and increased cellular invasion in vitro. Our data indicate that miR-34a could be a potential biomarker for improving the diagnostic efficiency of OC, and miR-34a overexpression may reduce OC pathogenesis by targeting FOXP1.

Identification of a forkhead box protein transcriptional network induced in human neutrophils in response to inflammatory stimuli

Introduction

Neutrophils represent the largest proportion of circulating leukocytes and, in response to inflammatory stimuli, are rapidly recruited to sites of infection where they neutralize pathogens.

Methods and results

We have identified a novel neutrophil transcription network induced in response to inflammatory stimuli. We performed the first RNAseq analysis of human neutrophils exposed to lipopolysaccharide (LPS), followed by a meta-analysis of our dataset and previously published studies of LPS-challenged neutrophils. This revealed a robustly enhanced transcriptional network driven by forkhead box (FOX) transcription factors. The network is enriched in genes encoding proinflammatory cytokines and transcription factors, including MAFF and ATF3, which are implicated in responses to stress, survival and inflammation. Expression of transcription factors FOXP1 and FOXP4 is induced in neutrophils exposed to inflammatory stimuli, and potential FOXP1/FOXP4 binding sites were identified in several genes in the network, all located in chromatin regions consistent with neutrophil enhancer function. Chromatin immunoprecipitation (ChIP) assays in neutrophils confirmed enhanced binding of FOXP4, but not FOXP1, to multiple sites in response to LPS. Binding to numerous motifs and transactivation of network genes were also observed when FOXP proteins were transiently expressed in HEK293 cells. In addition to LPS, the transcriptional network is induced by other inflammatory stimuli, indicating it represents a general neutrophil response to inflammation.

Discussion

Collectively, these findings reveal a role for the FOXP4 transcription network as a regulator of responses to inflammatory stimuli in neutrophils.

Multiple functions and regulatory network of miR-150 in B lymphocyte-related diseases

MicroRNAs (miRNAs) play vital roles in the post-transcriptional regulation of gene expression. Previous studies have shown that miR-150 is a crucial regulator of B cell proliferation, differentiation, metabolism, and apoptosis. miR-150 regulates the immune homeostasis during the development of obesity and is aberrantly expressed in multiple B-cell-related malignant tumors. Additionally, the altered expression of MIR-150 is a diagnostic biomarker of various autoimmune diseases. Furthermore, exosome-derived miR-150 is considered as prognostic tool in B cell lymphoma, autoimmune diseases and immune-mediated disorders, suggesting miR-150 plays a vital role in disease onset and progression. In this review, we summarized the miR-150-dependent regulation of B cell function in B cell-related immune diseases.

Neglected, yet significant role of FOXP1 in T-cell quiescence, differentiation and exhaustion

FOXP1 is ubiquitously expressed in the human body and is implicated in both physiological and pathological processes including cancer. However, despite its importance the role of FOXP1 in T-cells has not been extensively studied. Although relatively few phenotypic and mechanistic details are available, FOXP1 role in T-cell quiescence and differentiation of CD4+ subsets has recently been established. FOXP1 prevents spontaneous T-cell activation, preserves memory potential, and regulates the development of follicular helper and regulatory T-cells. Moreover, there is growing evidence that FOXP1 also regulates T-cell exhaustion. Altogether this makes FOXP1 a crucial and highly undervalued regulator of T-cell homeostasis. In this review, we discuss the biology of FOXP1 with a focus on discoveries made in T-cells in recent years.

Severe speech impairment is a distinguishing feature of FOXP1-related disorder

AIM

To delineate the speech and language phenotype of a cohort of individuals with FOXP1-related disorder.

METHOD

We administered a standardized test battery to examine speech and oral motor function, receptive and expressive language, non-verbal cognition, and adaptive behaviour. Clinical history and cognitive assessments were analysed together with speech and language findings.

RESULTS

Twenty-nine patients (17 females, 12 males; mean age 9y 6mo; median age 8y [range 2y 7mo-33y]; SD 6y 5mo) with pathogenic FOXP1 variants (14 truncating, three missense, three splice site, one in-frame deletion, eight cytogenic deletions; 28 out of 29 were de novo variants) were studied. All had atypical speech, with 21 being verbal and eight minimally verbal. All verbal patients had dysarthric and apraxic features, with phonological deficits in most (14 out of 16). Language scores were low overall. In the 21 individuals who carried truncating or splice site variants and small deletions, expressive abilities were relatively preserved compared with comprehension.

INTERPRETATION

FOXP1-related disorder is characterized by a complex speech and language phenotype with prominent dysarthria, broader motor planning and programming deficits, and linguistic-based phonological errors. Diagnosis of the speech phenotype associated with FOXP1-related dysfunction will inform early targeted therapy. What this paper adds Individuals with FOXP1-related disorder have a complex speech and language phenotype. Dysarthria, which impairs intelligibility, is the dominant feature of the speech profile. No participants were receiving speech therapy for dysarthria, but were good candidates for therapy Features of speech apraxia occur alongside persistent phonological errors. Language abilities are low overall; however, expressive language is a relative strength.

FOXP1 drives osteosarcoma development by repressing P21 and RB transcription downstream of P53

Osteosarcoma has a poor prognosis, and the poor understanding of the genetic drivers of osteosarcoma hinders further improvement in therapeutic approaches. Transcription factor forkhead box P1 (FOXP1) is a crucial modulator in skeletal development and aging. Here, we determined the role and regulatory mechanisms of FOXP1 in osteosarcoma. Higher FOXP1 expression correlated with malignancy in both osteosarcoma cell lines and clinical biopsies. FOXP1 overexpression and knockdown in osteosarcoma cell lines revealed that FOXP1 promoted proliferation, tumor sphere formation, migration and invasion, and inhibited anoikis. Mechanistically, FOXP1 acted as a repressor of P21 and RB (retinoblastoma protein) transcription, and directly interacted with the tumor suppressor p53 to inhibit its activity. Extracellular signal-regulated kinase/c-Jun N-terminal kinase (ERK/JNK) signaling and c-JUN/c-FOS transcription factors were found to be upstream activators of FOXP1. Moreover, FOXP1 silencing via lentivirus or adeno-associated virus (AAV)-mediated delivery of shRNA suppressed osteosarcoma development and progression in cell-derived and patient-derived xenograft animal models. Taken together, we demonstrate that FOXP1, which is transactivated by ERK/JNK-c-JUN/c-FOS, drives osteosarcoma development by regulating the p53-P21/RB signaling cascade, suggesting that FOXP1 is a potential target for osteosarcoma therapy.

CRISPR/Cas9-Mediated Foxp1 Silencing Restores Immune Surveillance in an Immunocompetent A20 Lymphoma Model

The interaction of lymphoma cells with their microenvironment has an important role in disease pathogenesis and is being actively pursued therapeutically using immunomodulatory drugs, including immune checkpoint inhibitors. Diffuse large B-cell lymphoma (DLBCL) is an aggressive high-grade disease that remains incurable in ~40% of patients treated with R-CHOP immunochemotherapy. The FOXP1 transcription factor is abundantly expressed in such high-risk DLBCL and we recently identified its regulation of immune response signatures, in particular, its suppression of the cell surface expression of major histocompatibility class II (MHC-II), which has a critical role in antigen presentation to T cells. Using CRISPR/Cas9 genome editing we have depleted Foxp1 expression in the aggressive murine A20 lymphoma cell line. When grown in BALB/c mice, this cell line provides a high-fidelity immunocompetent disseminated lymphoma model that displays many characteristics of human DLBCL. Transient Foxp1-depletion using siRNA, and stable depletion using CRISPR (generated by independently targeting Foxp1 exon six or seven) upregulated cell surface I-Ab (MHC-II) expression without impairing cell viability in vitro. RNA sequencing of Foxp1-depleted A20 clones identified commonly deregulated genes, such as the B-cell marker Cd19, and hallmark DLBCL signatures such as MYC-targets and oxidative phosphorylation. Immunocompetent animals bearing Foxp1-depleted A20 lymphomas showed significantly-improved survival, and 20% did not develop tumors; consistent with modulating immune surveillance, this was not observed in immunodeficient NOD SCIDγ mice. The A20 Foxp1 CRISPR model will help to further characterize the contribution of Foxp1 to lymphoma immune evasion and the potential for Foxp1 targeting to synergize with other immunotherapies.

The Roles of Alternative Splicing in Tumor-immune Cell Interactions

Alternative splicing (AS) plays a significant role in the hallmarks of cancer and can provide neoantigens for immunotherapy. Here, we summarize recent advances in immune system associated tumor specific-antigens (TSAs) produced by AS. We further discuss the regulating mechanisms involved in AS-mediated innate and adaptive immune responses and the anti-tumoral and protumoral roles in different types of cancer. For example, ULBP1_RI, MLL5Δ21spe, NKp44-1Δ5, MHC-IΔ7, CD200SΔ1, 2, PVR α/β/γ/δ and IL-33 variants 1/2/3 act as regulators in solid tumors and IPAK4-L and, FOXP1ΔN100 exhibit functions in hematological cancers.

Prognostic values and clinical implications of programmed cell death-ligand 1 (PD-L1), fork head transcription factor P-1 (FOXP-1) and signal transducer and activator of transcription-3 (STAT-3) expression in diffuse large B-cell lymphoma (DLBCL); an immunohistochemical study

Context

PD-L1 is an inhibitory ligand that functions as an essential immune checkpoint. FOXP-1 is a member of the FOXP family. STAT-3 plays a critical role in regulation of cell proliferation and survival. The detailed expression of the three markers together in DLBCL tissues and their prognostic value in patients with DLBCL were not fully investigated.

Aim was to assess the expression of PD-L1, FOXP-1 and STAT-3 in diffuse large B-cell lymphoma (DLBCL) and to correlate their expression with the pathological findings, prognostic parameters and clinical implications of patients.

Methods

PD-L1, FOXP-1 and STAT-3 were assessed in DLBCL tissues derived from 50 patients using immunohistochemistry. Patients were followed up for 3 years for response to therapy progression, recurrence and survival.

Results

High PD-L1 expression was associated with bone marrow involvement (p = 0.004), extra-nodal involvement (p = 0.006) and advanced stage (p = 0.003). High FOXP-1 expression was associated with presence of bone marrow involvement and high risk group (p < 0.001). High STAT-3 expression was associated with older age of the patient (p < 0.001), presence of bone marrow involvement (p = 0.002), extra-nodal involvement (p = 0.009), and high risk group (p = 0.005). High expression of PD-L1, FOXP-1 and STAT-3 was related to poor response to therapy, poor OS rate and RFS rates (p < 0.001).

Conclusion

High expression of PD-L1, FOXP-1 and STAT-3 was related poor prognosis in DLBCL patients.

PD-1/PD-L1 immune checkpoint and p53 loss facilitate tumor progression in activated B-cell diffuse large B-cell lymphomas

Refractory or relapsed diffuse large B-cell lymphoma (DLBCL) often associates with the activated B-cell-like (ABC) subtype and genetic alterations that drive constitutive NF-κB activation and impair B-cell terminal differentiation. Here, we show that DNA damage response by p53 is a central mechanism suppressing the pathogenic cooperation of IKK2ca-enforced canonical NF-κB and impaired differentiation resulting from Blimp1 loss in ABC-DLBCL lymphomagenesis. We provide evidences that the interplay between these genetic alterations and the tumor microenvironment select for additional molecular addictions that promote lymphoma progression, including aberrant coexpression of FOXP1 and the B-cell mutagenic enzyme activation-induced deaminase, and immune evasion through major histocompatibility complex class II downregulation, PD-L1 upregulation, and T-cell exhaustion. Consistently, PD-1 blockade cooperated with anti-CD20-mediated B-cell cytotoxicity, promoting extended T-cell reactivation and antitumor specificity that improved long-term overall survival in mice. Our data support a pathogenic cooperation among NF-κB-driven prosurvival, genetic instability, and immune evasion mechanisms in DLBCL and provide preclinical proof of concept for including PD-1/PD-L1 blockade in combinatorial immunotherapy for ABC-DLBCL.

Expression of NOTCH3 exon 16 differentiates Diffuse Large B-cell Lymphoma into molecular subtypes and is associated with prognosis

Diffuse large B-cell lymphoma (DLBCL) is a heterogeneous disease with diverse clinical presentation and outcome. Bio-clinical prognostic models including oncogene expression and cell-of-origin phenotyping has been developed, however, approximately 30% of all patients still die from their disease, illustrating the need for additional prognostic biomarkers associating oncogenesis and phenotypic subclasses. Hence, we tested if alternative splice variations have biomarker potential. Initial alternative splicing analysis of human exon array from clinical DLBCL samples identified candidate genes. Experimental validation by ddPCR was performed in a DLBCL cohort classified into ABC/GCB subclasses, B-cell associated gene signatures (BAGS: naive, centroblast, centrocyte, memory, and plasmablast), and vincristine resistant gene signatures. Prognostic potential was assessed for aberrantly spliced transcripts. Thus, NOTCH3 was identified as alternatively spliced, with differential exon 16 depletion (−exon 16) between differentiation associated BAGS subtypes. Predicted vincristine resistant patients of the GCB subclass had significantly downregulated NOTCH3 −exon 16 transcript expression and tended to display adverse overall survival for R-CHOP treated patients. In conclusion, we have identified a specific alternatively spliced NOTCH3 event that differentiate molecular subtypes of DLBCL and display prognostic and predictive biomarker potential in GCB DLBCL.

miR-150 downregulation contributes to the high-grade transformation of follicular lymphoma by upregulating FOXP1 levels

Follicular lymphoma (FL) is a common indolent B-cell malignancy with a variable clinical course. An unfavorable event in its course is histological transformation to a high-grade lymphoma, typically diffuse large B-cell lymphoma. Recent studies show that genetic aberrations of MYC or its overexpression are associated with FL transformation (tFL). However, the precise molecular mechanisms underlying tFL are unclear. Here we performed the first profiling of expression of microRNAs (miRNAs) in paired samples of FL and tFL and identified 5 miRNAs as being differentially expressed. We focused on one of these miRNAs, namely miR-150, which was uniformly downmodulated in all examined tFLs (∼3.5-fold), and observed that high levels of MYC are responsible for repressing miR-150 in tFL by binding in its upstream region. This MYC-mediated repression of miR-150 in B cells is not dependent on LIN28A/B proteins, which influence the maturation of miR-150 precursor (pri-miR-150) in myeloid cells. We also demonstrated that low miR-150 levels in tFL lead to upregulation of its target, namely FOXP1 protein, which is a known positive regulator of cell survival, as well as B-cell receptor and NF-κB signaling in malignant B cells. We revealed that low levels of miR-150 and high levels of its target, FOXP1, are associated with shorter overall survival in FL and suggest that miR-150 could serve as a good biomarker measurable in formalin-fixed paraffin-embedded tissue. Overall, our study demonstrates the role of the MYC/miR-150/FOXP1 axis in malignant B cells as a determinant of FL aggressiveness and its high-grade transformation.

MicroRNA miR-34a downregulates FOXP1 during DNA damage response to limit BCR signalling in chronic lymphocytic leukaemia B cells

The variable clinical course in chronic lymphocytic leukaemia (CLL) largely depends on p53 functionality and B-cell receptor (BCR) signalling propensity; however, it is unclear if there is any crosstalk between these pathways. We show that DNA damage response (DDR) activation leads to down-modulating the transcriptional factor FOXP1, which functions as a positive BCR signalling regulator and its high levels are associated with worse CLL prognosis. We identified microRNA (miRNA) miR-34a as the most prominently upregulated miRNA during DDR in CLL cells in vitro and in vivo during FCR therapy (fludarabine, cyclophosphamide, rituximab). MiR-34a induced by DDR activation and p53 stabilization potently represses FOXP1 expression by binding in its 3'-UTR. The low FOXP1 levels limit BCR signalling partially via derepressing BCR-inhibitory molecule CD22. We also show that low miR-34a levels can be used as a biomarker for worse response or shorter progression free survival in CLL patients treated with FCR chemoimmunotherapy, and shorter overall survival, irrespective of TP53 status. Additionally, we have developed a method for the absolute quantification of miR-34a copies and defined precise prognostic/predictive cutoffs. Overall, herein, we reveal for the first time that B cells limit their BCR signalling during DDR by down-modulating FOXP1 via DDR-p53/miR-34a axis.