Transcriptional Regulation of Human CD5: Important Role of Ets Transcription Factors in CD5 Expression in T Cells

Thymic Carcinoma: Unraveling Neuroendocrine Differentiation and Epithelial Cell Identity Loss

BACKGROUND

The histogenesis of thymic epithelial tumors (TETs) has been a subject of debate. Recent technological advancements have revealed that thymic carcinomas often exhibit a phenotype akin to tuft cells, which is a subset of medullary TECs. Here, we further explored the gene expression signatures of thymic carcinomas in relation to tuft cells and their kinships-ionocytes and neuroendocrine cells (neuroendocrine group).

METHODS

We analyzed a single-cell RNA sequencing dataset from the normal human thymus. Concurrently, we examined publicly available datasets on the mRNA expression and methylation status of TECs and lung cancers. Real-time quantitative PCR was also conducted with our tissue samples.

RESULTS

Thymic carcinomas displayed a neuroendocrine phenotype biased toward tuft cells and ionocytes. When exploring the possible regulators of this phenotype, we discovered that HDAC9 and NFATC1 were characteristically expressed in the neuroendocrine group in adult TECs and thymic carcinomas. Additionally, the pan-thymic epithelium markers, exemplified by PAX9 and SIX1, were significantly suppressed in thymic carcinomas.

CONCLUSIONS

Thymic carcinomas might be characterized by unique neuroendocrine differentiation and loss of identity as thymic epithelial cells. Future studies investigating the role of HDAC9 and NFATC1 in thymic epithelium are warranted to explore their potential as therapeutic targets in TETs.

Low Expression of CD5 and CD6 Is Associated with Poor Overall Survival for Patients with T-Cell Malignancies

Background

T-cell malignancies (TCMs), including T-cell acute lymphoblastic leukemia (T-ALL) and T-cell lymphoma (TCL), are highly aggressive and have a poor prognosis. To further understand prognostic stratifications and to design targeted therapies, this study aims to explore novel, potential biomarkers based on alterations in immune costimulatory molecules (CMs) for TCMs.

Methods

Peripheral blood from 25 de novo T-ALL patients in our clinical center and transcriptome data from 131 to 162 patients with peripheral TCL (PTCL) from the GSE19069 and GSE58445 dataset, respectively, were obtained to assess the expression levels of CMs and their prognostic significance.

Results

Seven CMs were associated with overall survival (OS). Among these CMs, CD5 and CD6 had the highest pairwise positive correlation (R = 0.69). CD5 and CD6 were significantly down-regulated in TCM patients compared with healthy individuals (HIs), and lower CD5 and CD6 expression was associated with poor OS for both T-ALL and TCL patients, particularly for patients greater than 60 years old. Furthermore, CD5 was positively correlated with CD6 in TCM patients. Compared with patients who were CD5^highCD6^high, T-ALL and TCL patients who were CD5^lowCD6^low had poor OS. Importantly, CD5^highCD6^high was an independent prognostic predictor for OS in T-ALL (HR = 0.39, 95% CI: 0.23–0.65, P < 0.001) and TCL (HR = 0.35, 95% CI: 0.19–0.62, P < 0.001) patients.

Conclusions

Low expression of CD5 and CD6 was associated with poor OS for TCM patients, and this may be a potential immune biomarker panel for prognostic stratification of TCM patients.

Pre-existing chromatin accessibility and gene expression differences among naive CD4+ T cells influence effector potential

CD4+ T cells have a remarkable potential to differentiate into diverse effector lineages following activation. Here, we probe the heterogeneity present among naive CD4+ T cells before encountering their cognate antigen to ask whether their effector potential is modulated by pre-existing transcriptional and chromatin landscape differences. Single-cell RNA sequencing shows that key drivers of variability are genes involved in T cell receptor (TCR) signaling. Using CD5 expression as a readout of the strength of tonic TCR interactions with self-peptide MHC, and sorting on the ends of this self-reactivity spectrum, we find that pre-existing transcriptional differences among naive CD4+ T cells impact follicular helper T (TFH) cell versus non-TFH effector lineage choice. Moreover, our data implicate TCR signal strength during thymic development in establishing differences in naive CD4+ T cell chromatin landscapes that ultimately shape their effector potential.

CD5 and CD6 as immunoregulatory biomarkers in non-small cell lung cancer

BACKGROUND

The study of immune surveillance in the tumour microenvironment is leading to the development of new biomarkers and therapies. The present research focuses on the expression of CD5 and CD6-two lymphocyte surface markers involved in the fine tuning of TCR signaling-as potential prognostic biomarkers in resectable stages of non-small cell lung cancer (NSCLC).

METHODS

CD5 and CD6 gene expression was analysed by reverse transcription quantitative polymerase chain reaction (RTqPCR) in 186 paired fresh frozen tumour and normal tissue samples of resected NSCLC.

RESULTS

Patients with higher CD5 expression had significantly increased overall survival (OS, 49.63 vs. 99.90 months, P=0.013). CD5 expression levels were correlated to CD4 infiltration and expression levels, and survival analysis showed that patients with a higher CD5/CD4 + ratio had significantly improved prognosis. Multivariate analysis established CD5 expression as an independent prognostic biomarker for OS in early stages of NSCLC (HR=0.554; 95% CI, 0.360-0.853; P=0.007). Further survival analysis of NSCLC cases (n=97) from The Cancer Genome Atlas (TCGA) database, confirmed the prognostic value of both CD5 and CD6 expression¸ although CD6 expression alone did not reach significant prognostic value in our NSCLC training cohort.

CONCLUSIONS

Our data support further studies on CD5 and CD6 as novel prognostic markers in resectable NSCLC and other cancer types (i.e., melanoma), as well as a role for these receptors in immune surveillance.

Greater frequency of CD5-negative CD8(+) T cells against human immunodeficiency virus type 1 than other viruses is consistent with adaptation to antigenic variation

BACKGROUND

The CD5 protein antagonizes phosphorylation events downstream of T cell receptor (TCR) engagement to decrease T cell responsiveness. CD5-negative T cell clones respond preferentially over their CD5(+) counterparts against cells with low human histocompatibility-linked leukocyte antigen (HLA) levels. In human immunodeficiency virus type 1 (HIV-1) infection, CD5(-)CD8(+) T cells increase in prevalence with disease progression.

METHODS

To investigate potential causes of this expansion of CD5(-)CD8(+) T cells in HIV-1 infection, we compared CD5 expression on CD8(+) T cells reactive against HIV-1 peptides, common viral peptides and a self peptide that together span a broad range of TCR avidities in the context of the common HLA-A2 class I restriction molecule. Following stimulation, CD5 expression on peptide-specific CD8(+) T cells was assessed by flow cytometry.

RESULTS

In healthy controls, there was no significant difference in the CD5(+) percentage of CD8(+) T cells specific for common viral peptides, but a lower percentage of those responding against a common self peptide expressed CD5. The same relationship occurred in HIV-infected individuals, however, a lower percentage of HIV peptide-specific CD8(+) T cells than other viral peptide-specific CD8(+) T cells expressed CD5. In terms of overall CD5 expression level at the peptide-specific responder population level, HIV-specific CD8(+) T cells resembled those responsive against the self peptide, despite much higher avidity TCR/HLA/peptide interactions.

CONCLUSIONS

This deficit in CD5 expression selective for HIV-specific CD8(+) T cells is consistent with in vivo adaptation to low avidity HIV peptide variants and has potential consequences for CD8(+) T cell expansion, cross-reactivity and autoreactivity.

Basic science for the clinician 54: CD5

The full story of what surface markers mean about the cells on which they reside twists and turns as the days go by, with previously accepted "truth" changing in light of new findings. Such is the case with CD5, a surface marker on most murine T cells, many thymocytes, and a subset of B cells. The precise role of CD5 in the murine and human immune responses has been a matter of intense speculation for many years. Recent work suggests that CD5 may have a fine-tuning or suppressive effect on signaling through the antigen receptors on both B and T cells. These CD5 B cells were initially thought to be a major source of autoantibodies and/or "natural antibodies," targeting broad arrays of carbohydrate and protein antigens. More recent studies support the latter contention-CD5 B cells do produce "natural antibodies," but the former is far from true-CD5 B cells are not the major source of autoantibodies. In fact, CD5 may be a major negative influence on antigen receptor driven-B-cell function and may serve to control autoimmunity rather than encourage it. Furthermore, another subset of CD5 B cells may represent a distinct regulatory population. CD5 expression is noted on more than three fourths of all T-cell lymphomas. CD5 may be a receptor of pathogen-associated molecular patterns; CD5 may be a marker of decreased dependence of B cells on certain circulating factors. Elevated levels of CD5 are found in a number of autoimmune disorders. Thus, although the precise mechanism is unclear, there is at the very least circumstantial evidence of a role for CD5 in the pathogenesis of autoimmunity and perhaps T cell-derived lymphoid malignancy. New findings put old claims to rest and open up new avenues for research, both basic and clinical, with therapeutic applications not far behind.

Differential transcription factor use by the KIR2DL4 promoter under constitutive and IL-2/15-treated conditions

KIR2DL4 is unique among human KIR genes in expression, cellular localization, structure, and function, yet the transcription factors required for its expression have not been identified. Using mutagenesis, EMSA, and cotransfection assays, we identified two redundant Runx binding sites in the 2DL4 promoter as essential for constitutive 2DL4 transcription, with contributions by a cyclic AMP response element (CRE) and initiator elements. IL-2- and IL-15-stimulated human NK cell lines increased 2DL4 promoter activity, which required functional Runx, CRE, and Ets sites. Chromatin immunoprecipitation experiments show that Runx3 and Ets1 bind the 2DL4 promoter in situ. 2DL4 promoter activity had similar transcription factor requirements in T cells. Runx, CRE, and Ets binding motifs are present in 2DL4 promoters from across primate species, but other postulated transcription factor binding sites are not preserved. Differences between 2DL4 and clonally restricted KIR promoters suggest a model that explains the unique 2DL4 expression pattern in human NK cells.

Mechanisms elevating ORMDL3 expression in recurrent wheeze patients: role of Ets-1, p300 and CREB

The first genetic factor identified for childhood asthma by genome-wide association study (GWAS) is the locus on chromosome 17q21, harboring the Orosomucoid 1-like 3 (ORMDL3) gene. ORMDL3 is implicated in facilitation of endoplasmic reticulum-mediated inflammatory responses, believed to underlie its association with asthma. In the present study, we demonstrated that mRNA expression of ORMDL3 is significantly increased in the peripheral blood of recurrent wheeze patients compared with normal control subjects by real-time RT-PCR. To elucidate the molecular mechanisms involved in human ORMDL3 regulation, we cloned and characterized the promoter region of ORMDL3. Applying 5'-rapid amplification of cDNA end analysis (RACE), we revealed that ORMDL3 gene used multiple transcriptional start sites (TSSs). Using a series of 5' deletion promoter plasmids in luciferase reporter assays, we identified that the proximal minimal promoter of ORMDL3 was located within the region -84/+58 relative to the TSS. Mutational analysis, RNA interference experiments and sequential chromatin immunoprecipitation (ChIP) assay demonstrated that transcriptional activity of the ORMDL3 gene was cooperatively regulated by multiple transcription factors, including Ets-1, p300 and CREB. The expression levels of Ets-1, p300 and CREB were increased in the peripheral blood of recurrent wheeze patients compared with normal control subjects and showed a strong linear correlation with the expression of ORMDL3. Our findings indicate that Ets-1, p300 and CREB binding to the promoter region drive the ORMDL3 transcription.

Rescue of tumor-infiltrating lymphocytes from activation-induced cell death enhances the antitumor CTL response in CD5-deficient mice

The CD5 coreceptor is expressed on all T cells and on the B1a B cell subset. It is associated with TCR and BCR, and modulates intracellular signals initiated by both Ag receptor complexes. Human CD5 contributes to regulation of the antitumor immune response and susceptibility of specific CTL to activation-induced cell death (AICD) triggered by the tumor. In this study, we compared the T cell response to the B16F10 melanoma engrafted into CD5-deficient and wild-type C57BL/6 mice. Compared with wild-type mice, CD5 knockout animals displayed delayed tumor growth, associated with tumor infiltration by T cell populations exhibiting a more activated phenotype and enhanced antitumor effector functions. However, control of tumor progression in CD5(-/-) mice was transient due to increased AICD of CD8(+) tumor-infiltrating T lymphocytes. Remarkably, in vivo protection of T cells from TCR-mediated apoptosis by an adenovirus engineered to produce soluble Fas resulted in a dramatic reduction in tumor growth. Our data suggest that recruitment of tumor-specific T cells in the tumor microenvironment occurs at early stages of cancer development and that tumor-mediated AICD of tumor-infiltrating T lymphocytes is most likely involved in tumor escape from the immune system.

Rationale for Targeting CD6 as a Treatment for Autoimmune Diseases

CD6 is a 105–130 kDa surface glycoprotein expressed on the majority of T cells and a subset of B cells. The human cd6 gene maps to chromosome 11, and the expression of its protein product is tightly regulated. CD6 mediates cellular adhesion migration across the endothelial and epithelial cells. In addition, it participates in the antigen presentation by B cells and the subsequent proliferation of T cells. CD6 may bind in trans to surface glycoproteins (such as ALCAM and 3A11), or to microbial lipopolysaccharides, and may bind in cis to endogenous ligands (such as CD3 and CD5), and thereby deliver a costimulatory signal. Transinteractions are reinforced during autoimmune diseases (e.g., rheumatoid arthritis (RA), Sjögren's syndrome, and multiple sclerosis) and some cancers. Based on experimental data and on clinical results in RA and psoriasis, we believe that the recent humanized anti-CD6-specific mAb T1h may act as a regulator of the immunological response in addition to its function as an anti-T- and -B cell agent.

A conserved enhancer element differentially regulates developmental expression of CD5 in B and T cells

We previously identified an enhancer element upstream of the mouse cd5 gene that was required in reporter assays for the induction of cd5 promoter activity by BCR cross-linking. This element is highly conserved in placental mammals. To determine its physiological role, we have now generated mice with a targeted deletion of the enhancer. The result is the loss of CD5 expression in peritoneal and splenic B-1a cells of adult mice and an inability to induce CD5 by cross-linking of the BCR on splenic B-2 cells. Surprisingly, CD5 expression on B-1a cells of neonatal mice was only minimally compromised. Cd5 enhancer deletion also had only a modest effect on CD5 expression in the T lineage. Thus, this enhancer provides age- and tissue-specific regulation of CD5 expression and is an example of the utilization of different modes of regulation of expression in T and B cells.

The transcription factor Ets1 is important for CD4 repression and Runx3 up-regulation during CD8 T cell differentiation in the thymus

The transcription factor Ets1 contributes to the differentiation of CD8 lineage cells in the thymus, but how it does so is not understood. In this study, we demonstrate that Ets1 is required for the proper termination of CD4 expression during the differentiation of major histocompatability class 1 (MHC I)–restricted thymocytes, but not for other events associated with their positive selection, including the initiation of cytotoxic gene expression, corticomedullary migration, or thymus exit. We further show that Ets1 promotes expression of Runx3, a transcription factor important for CD8 T cell differentiation and the cessation of Cd4 gene expression. Enforced Runx3 expression in Ets1-deficient MHC I–restricted thymocytes largely rescued their impaired Cd4 silencing, indicating that Ets1 is not required for Runx3 function. Finally, we document that Ets1 binds at least two evolutionarily conserved regions within the Runx3 gene in vivo, supporting the possibility that Ets1 directly contributes to Runx3 transcription. These findings identify Ets1 as a key player during CD8 lineage differentiation and indicate that it acts, at least in part, by promoting Runx3 expression.

IL-10 production by B cells expressing CD5 with the alternative exon 1B

B lymphocytes are divided into two subpopulations, B1 and B2 cells based on expression of the T cell-associated protein CD5. Natural B1 cells are further divided into B1a cells that express CD5 on their membrane and B1b cells that do not but share most other biological characteristics of B1a cells. Recent studies from our laboratory have revealed, in humans, the existence of two alternative isoforms of the CD5 protein. A cell surface CD5 isoform which uses exon 1A (E1A) of the gene in B1a cells, and an intracellular isoform which uses exon 1B (E1B) mainly in human B1b cells. Indeed, the protein isoform encoded by transcripts containing E1B lack the leader peptide and is, thus, retained in the cytoplasm of B cells. The restriction of interleukin (IL)-10 to B1 lymphocytes in the mouse raises the possibility that the human CD5-E1B-expressing B cells produce IL-10. This prediction was confirmed in the CD5 negative Jok-1 B cells transfected with cDNA for either isoforms resulted in high level IL-10 production. Our data indicate that E1B-CD5-expressing B cells have the capacity to interfere with the immune response through their ability to produce high levels of IL-10.

Regulation of natriuretic peptide receptor-A gene expression and stimulation of its guanylate cyclase activity by transcription factor Ets-1

ANP (atrial natriuretic peptide) exerts its biological effects by binding to GC (guanylate cyclase)-A/NPR (natriuretic peptide receptor)-A, which generates the second messenger cGMP. The molecular mechanism mediating Npr1 (coding for GC-A/NPRA) gene regulation and expression is not well understood. The objective of the present study was to elucidate the mechanism by which Ets-1 [Ets (E twenty-six) transformation-specific sequence] contributes to the regulation of Npr1 gene transcription and expression. Chromatin immunoprecipitation and gel-shift assays confirmed the in vivo and in vitro binding of Ets-1 to the Npr1 promoter. Overexpression of Ets-1 enhanced significantly Npr1 mRNA levels, protein expression, GC activity and ANP-stimulated intracellular accumulation of cGMP in transfected cells. Depletion of endogenous Ets-1 by siRNA (small interfering RNA) dramatically decreased promoter activity by 80%. Moreover, methylation of the Npr1 promoter region (-356 to +55) reduced significantly the promoter activity and hypermethylation around the Ets-1 binding sites directly reduced Ets-1 binding to the Npr1 promoter. Collectively, the present study demonstrates that Npr1 gene transcription and GC activity of the receptor are critically controlled by Ets-1 in target cells.

Transcriptional regulation of mouse L-selectin

L-selectin mediates the initial tethering and rolling of lymphocytes in high endothelial venules. To study the transcriptional regulation of mouse L-selectin, we cloned 4.5 kb 5'-flanking sequences of the mouse sell. Luciferase analysis of serial 5'-deletion mutants showed that the first 285 bp was sufficient to drive high promoter activity in EL4 cells, but not in Sell-negative HeLa cells, suggesting that this fragment harbors the minimal mouse sell promoter and contains cis-elements for lymphocyte-specific expression. Site-directed mutagenesis and chromatin immunoprecipitation showed that Mzf1, Klf2, Sp1, Ets1, and Irf1 bind to and activate the mouse sell promoter. Over expression of these transcription factors in EL4 cells increased expression of sell mRNA. Silencing the expression of Sp1 by siRNA significantly decreased sell promoter activity in EL4 cells. We conclude that sell transcription is regulated by Mzf1, Klf2, Sp1, Ets1, and Irf1.

PU.1 and ICSBP control constitutive and IFN-gamma-regulated Tlr9 gene expression in mouse macrophages

Macrophages are activated by unmethylated CpG-containing DNA (CpG DNA) via TLR9. IFN-gamma and LPS can synergize with CpG DNA to enhance proinflammatory responses in murine macrophages. Here, we show that LPS and IFN-gamma up-regulated Tlr9 mRNA in murine bone marrow-derived macrophages (BMM). The ability of LPS and IFN-gamma to induce Tlr9 mRNA expression in BMM was dependent on the presence of the growth factor, CSF-1, which is constitutively present in vivo. However, there were clear differences in mechanisms of Tlr9 mRNA induction. LPS stimulation rapidly removed the CSF-1 receptor (CSF-1R) from the cell surface, thereby blocking CSF-1-mediated transcriptional repression and indirectly inducing Tlr9 mRNA expression. By contrast, IFN-gamma activated the Tlr9 promoter directly and only marginally affected cell surface CSF-1R expression. An approximately 100-bp proximal promoter of the murine Tlr9 gene was sufficient to confer basal and IFN-gamma-inducible expression in RAW264.7 cells. A composite IFN regulatory factor (IRF)/PU.1 site upon the major transcription start site was identified. Mutation of the binding sites for PU.1 or IRF impaired basal promoter activity, but only the IRF-binding site was required for IFN-gamma induction. The mRNA expression of the IRF family member IFN consensus-binding protein [(ICSBP)/IRF8] was coregulated with Tlr9 in macrophages, and constitutive and IFN-gamma-inducible Tlr9 mRNA expression was reduced in ICSBP-deficient BMM. This study therefore characterizes the regulation of mouse Tlr9 expression and defines a molecular mechanism by which IFN-gamma amplifies mouse macrophage responses to CpG DNA.

B cell hyperresponsiveness and expansion of mature follicular B cells but not of marginal zone B cells in NFATc2/c3 double-deficient mice

Marginal zone (MZ) B cells and peritoneal B-1 cells provide a first defense system of thymus-independent Ab responses against foreign pathogens and therefore share a number of functional properties. Recently, development of B-1a cells was shown to be controlled by the transcription factor NFATc1. We show here that mice deficient for NFATc2 and c3 display a distinct lower representation of MZ B cells, which is correlated with a reduced capturing of trinitrophenyl-Ficoll. In contrast, mature follicular B cells from NFATc2/c3-/- mice are strongly increased in number. NFATc2/c3-/- B cells exhibit a marked increase in BCR-induced intracellular Ca2+ mobilization and proliferation. However, trinitrophenyl-Ficoll-specific IgM and IgG3 responses of NFATc2/c3-deficient mice are intact, and chimeric mice reconstituted with NFATc2/3-deficient B cells show a normal number of MZ B cells and normal BCR responses. These observations suggest that the strongly elevated Th2 cytokine milieu in NFATc2/c3-deficient mice leads to a hyperactivation of mature, follicular B cells, whereas MZ B cells are less responsive to these signals.