An Id-related helix-loop-helix protein encoded by a growth factor-inducible gene

The divergence between T cell and innate lymphoid cell fates controlled by E and Id proteins

T cells develop in the thymus from lymphoid primed multipotent progenitors or common lymphoid progenitors into αβ and γδ subsets. The basic helix-loop-helix transcription factors, E proteins, play pivotal roles at multiple stages from T cell commitment to maturation. Inhibitors of E proteins, Id2 and Id3, also regulate T cell development while promoting ILC differentiation. Recent findings suggest that the thymus can also produce innate lymphoid cells (ILCs). In this review, we present current findings that suggest the balance between E and Id proteins is likely to be critical for controlling the bifurcation of T cell and ILC fates at early stages of T cell development.

Discovery of novel ID2 antagonists from pharmacophore-based virtual screening as potential therapeutics for glioma

Glioma, especially the most aggressive type glioblastoma multiforme, is a malignant cancer of the central nervous system with a poor prognosis. Traditional treatments are mainly surgery combined with radiotherapy and chemotherapy, which is still far from satisfactory. Therefore, it is of great clinical significance to find new therapeutic agents. Serving as an inhibitor of differentiation, protein ID2 (inhibitor of DNA binding 2) plays an important role in neurogenesis, neovascularization and malignant development of gliomas. It has been shown that ID2 affects the malignant progression of gliomas through different mechanisms. In this study, a pharmacophore-based virtual screening was carried out and 16 hit compounds were purchased for pharmacological evaluations on their ID2 inhibitory activities. Based on the cytotoxicity of these small-molecule compounds, two compounds were shown to effectively inhibit the viability of glioma cells in the micromolar range. Among them, AK-778-XXMU was chosen for further study due to its better solubility in water. A SPR (Surface Plasma Resonance) assay proved the high affinity between AK-778-XXMU and ID2 protein with the K_D value as 129 nM. The plausible binding mode of ID2 was studied by molecular docking and it was found to match AGX51 very well in the same binding site. Subsequently, the cancer-suppressing potency of the compound was characterized both in vitro and in vivo. The data demonstrated that compound AK-778-XXMU is a potent ID2 antagonist which has the potential to be developed as a therapeutic agent against glioma.

Screening of host genes regulated by ID1 and ID3 proteins during foot-and-mouth disease virus infection

Foot-and-mouth disease virus (FMDV) is an important pathogen that harms cloven-hoofed animals and has caused serious losses to livestock production since its discovery. Furthermore, inhibitor of DNA binding (ID) proteins have been thoroughly studied in tumorigenesis, differentiation and metastasis, but its role in viral infection is rarely known. In this study, three gene knockout cell lines ID1 KO, ID3 KO, ID1/3 KO were obtained based on BHK-21 cells. We found that ID1 and ID3 genes single or double knockout promote the replication of FMDV. Moreover, compared with negative control cells during virus infection, there were 551 up-regulated genes and 1222 down-regulated genes in the ID1 KO cell line; 916 up-regulated genes and 1845 down-regulated genes in the ID3 KO cell line; 810 up-regulated genes and 1566 down-regulated genes in ID1/3 KO cell line. Further genes expression patterns verification results also showed a good correlation between the data of RT-qRCR and RNA-seq. These findings provide a basis for studying the relevant mechanisms between host genes and ID genes during FMDV infection.

Hearing Loss in Id1-/-; Id3+/- and Id1+/-; Id3-/- Mice Is Associated With a High Incidence of Middle Ear Infection (Otitis Media)

Inhibitors of differentiation/DNA binding (Id) proteins are crucial for inner ear development, but whether Id mutations affect middle ear function remains unknown. In this study, we obtained Id1-/-; Id3+/- mice and Id1+/-; Id3-/- mice and carefully examined their middle ear morphology and auditory function. Our study revealed a high incidence (>50%) of middle ear infection in the compound mutant mice. These mutant mice demonstrated hearing impairment starting around 30 days of age, as the mutant mice presented elevated auditory brainstem response (ABR) thresholds compared to those of the littermate controls. The distortion product of otoacoustic emission (DPOAE) was also used to evaluate the conductive function of the middle ear, and we found much lower DPOAE amplitudes in the mutant mice, suggesting sound transduction in the mutant middle ear is compromised. This is the first study of the middle ears of Id compound mutant mice, and high incidence of middle ear infection determined by otoscopy and histological analysis of middle ear suggests that Id1/Id3 compound mutant mice are a novel model for human otitis media (OM).

Id(entifying) the inhibitor of DNA binding 3 in the brain of Nothobranchius furzeri upon aging

Inhibitors of DNA (Id) are key transcription factors (TFs) regulating neurogenic processes. They belong to the helix-loop-helix (HLH) TF family and are dominant negative regulators of basic HLH proteins (bHLHs). Specifically, they inhibit cell differentiation and enhance cell proliferation and motility. The Id family includes four members, Id1, Id2, Id3, and Id4, which have been identified in nearly all vertebrates. The transcript catalog of the African turquoise killifish, Nothobranchius furzeri, contains all four TFs and has evolved showing positive selection for Id3. N. furzeri, a teleost, is the short-lived vertebrate and is gaining increasing scientific interest as a new model organism in aging research. It is characterized by embryonic diapause, explosive sexual maturation, and rapid aging. In this study, we investigated both the expression and the role of Id3 in the brain of this model organism. Interestingly, Id3 was upregulated age-dependently along with a distribution pattern resembling that of other vertebrates. Additionally, the gene has undergone positive selection during evolution and shows a high degree of conservation relative to that of other vertebrates. These features make N. furzeri a valid tool for aging studies and a potential model in translational research.

Role of inhibitor of differentiation 3 gene in cellular differentiation of human corneal stromal fibroblasts

Purpose

Inhibitor of differentiation (Id) proteins are helix-loop-helix (HLH) transcriptional repressors that modulate a range of developmental and cellular processes, including cell differentiation and cell cycle mobilization. The inhibitor of differentiation 3 (Id3) gene, a member of the Id gene family, governs the expression and progression of transforming growth factor beta (TGFβ)-mediated cell differentiation. In the face of mechanical, chemical, or surgical corneal insults, corneal keratocytes differentiate into myofibroblasts for wound repair. Excessive development or persistence or both of myofibroblasts after wound repair results in corneal haze that compromises corneal clarity and visual function. The objective of this study was to investigate whether Id3 overexpression in human corneal stromal fibroblasts governs TGFβ-driven cellular differentiation and inhibits keratocyte to myofibroblast transformation.

Methods

Primary human corneal stromal fibroblast (h-CSF) cultures were generated from donor human corneas. Human corneal myofibroblasts (h-CMFs) were produced by growing h-CSF in the presence of TGFβ1 under serum-free conditions. The Id3 gene was cloned into a mammalian expression vector (pcDNA3 mCherry LIC cloning vector), and the nucleotide sequence of the vector constructs was confirmed with sequencing as well as through restriction enzyme analysis. The Id3 mammalian overexpression vector was introduced into h-CSFs using a lipofectamine transfection kit. The expression of Id3 in selected clones was characterized with quantitative real-time PCR (qRT-PCR), immunocytochemistry, and western blotting. Phase contrast microscopy and trypan blue exclusion assays were used to evaluate the effects of the transfer of the Id3 gene on the hCSF phenotype and viability, respectively. To analyze the inhibitory effects of the Id3 gene transfer on TGFβ-induced formation of h-CMFs, expression of the mRNA and protein of the myofibroblast marker alpha smooth muscle actin (α-SMA) was examined with qRT-PCR, western blotting, and immunocytochemistry. Student t test, analysis of variance (ANOVA), and Bonferroni adjustment for repeated measures were used for statistical analysis.

Results

The results indicate that Id3 overexpression does not alter the cellular phenotype or viability of h-CSFs. Overexpression of the Id3 gene in h-CSF cells grown in the presence of TGFβ1 under serum-free conditions showed a statistically significant decrease (76.3±4.3%) in α-SMA expression (p<0.01) compared to the naked-vector transfected or non-transfected h-CSF cells. Id3-transfected, naked-vector transfected, and non-transfected h-CSF cells grown in the absence of TGFβ1 showed the expected low expression of α-SMA (0-5%). Furthermore, Id3 overexpression statistically significantly decreased TGFβ-induced mRNA levels of profibrogenic genes such as fibronectin, collagen type I, and collagen type IV (1.80±0.26-, 1.70±0.35- and 1.70±0.36-fold, respectively; p<0.05) that a play role in stromal matrix modulation and corneal wound healing. Results of the protein analysis with western blotting indicated that Id3 overexpression in h-CSF cells effectively slows TGFβ-driven differentiation and formation of h-CMFs. Results for subsequent overexpression studies showed that this process occurs through the regulation of E2A, a TATA box protein.

Conclusions

Id3 regulates TGFβ-driven differentiation of h-CSFs and formation of h-CMFs in vitro. Targeted Id3 gene delivery has potential to treat corneal fibrosis and reestablish corneal clarity in vivo.

Emerging Roles of Inhibitor of Differentiation-1 in Alzheimer's Disease: Cell Cycle Reentry and Beyond

Inhibitor of DNA-binding/differentiation (Id) proteins, a family of helix-loop-helix (HLH) proteins that includes four members of Id1 to Id4 in mammalian cells, are critical for regulating cell growth, differentiation, senescence, cell cycle progression, and increasing angiogenesis and vasculogenesis, as well as accelerating the ability of cell migration. Alzheimer’s disease (AD), the most common neurodegenerative disease in the adult population, manifests the signs of cognitive decline, behavioral changes, and functional impairment. The underlying mechanisms for AD are not well-clarified yet, but the aggregation of amyloid-beta peptides (Aβs), the major components in the senile plaques observed in AD brains, contributes significantly to the disease progression. Emerging evidence reveals that aberrant cell cycle reentry may play a central role in Aβ-induced neuronal demise. Recently, we have shown that several signaling mediators, including Id1, hypoxia-inducible factor-1 (HIF-1), cyclin-dependent kinases-5 (CDK5), and sonic hedgehog (Shh), may contribute to Aβ-induced cell cycle reentry in postmitotic neurons; furthermore, Id1 and CDK5/p25 mutually antagonize the expression/activity of each other. Therefore, Id proteins may potentially have clinical applications in AD. In this review article, we introduce the underlying mechanisms for cell cycle dysregulation in AD and present some examples, including our own studies, to show different aspects of Id1 in terms of cell cycle reentry and other signaling that may be crucial to alter the neuronal fates in this devastating neurodegenerative disease. A thorough understanding of the underlying mechanisms may provide a rationale to make an earlier intervention before the occurrence of cell cycle reentry and subsequent apoptosis in the fully differentiated neurons during the progression of AD or other neurodegenerative diseases.

Inhibitor of DNA binding in heart development and cardiovascular diseases

Id proteins, inhibitors of DNA binding, are transcription regulators containing a highly conserved helix-loop-helix domain. During multiple stages of normal cardiogenesis, Id proteins play major roles in early development and participate in the differentiation and proliferation of cardiac progenitor cells and mature cardiomyocytes. The fact that a depletion of Ids can cause a variety of defects in cardiac structure and conduction function is further evidence of their involvement in heart development. Multiple signalling pathways and growth factors are involved in the regulation of Ids in a cell- and tissue- specific manner to affect heart development. Recent studies have demonstrated that Ids are related to multiple aspects of cardiovascular diseases, including congenital structural, coronary heart disease, and arrhythmia. Although a growing body of research has elucidated the important role of Ids, no comprehensive review has previously compiled these scattered findings. Here, we introduce and summarize the roles of Id proteins in heart development, with the hope that this overview of key findings might shed light on the molecular basis of consequential cardiovascular diseases. Furthermore, we described the future prospective researches needed to enable advancement in the maintainance of the proliferative capacity of cardiomyocytes. Additionally, research focusing on increasing embryonic stem cell culture adaptability will help to improve the future therapeutic application of cardiac regeneration.

CCAAT/Enhancer Binding Protein β inhibits myogenic differentiation via ID3

Myogenesis is regulated by the coordinated expression of muscle regulatory factors, a family of transcription factors that includes MYOD, MYF5, myogenin and MRF4. Muscle regulatory factors are basic helix-loop-helix transcription factors that heterodimerize with E proteins to bind the regulatory regions of target genes. Their activity can be inhibited by members of the Inhibitor of DNA binding and differentiation (ID) family, which bind E-proteins with high affinity, thereby preventing muscle regulatory factor-dependent transcriptional responses. CCAAT/Enhancer Binding protein beta (C/EBPβ) is a transcription factor expressed in myogenic precursor cells that acts to inhibit myogenic differentiation, though the mechanism remains poorly understood. We identify Id3 as a novel C/EBPβ target gene that inhibits myogenic differentiation. Overexpression of C/EBPβ stimulates Id3 mRNA and protein expression, and is required for C/EBPβ-mediated inhibition of myogenic differentiation. Misexpression of C/EBPβ in myogenic precursors, such as in models of cancer cachexia, prevents the differentiation of myogenic precursors and we show that loss of Id3 rescues differentiation under these conditions, suggesting that the stimulation of Id3 expression by C/EBPβ is an important mechanism by which C/EBPβ inhibits myogenic differentiation.

The role of inhibitor of binding or differentiation 2 in the development and differentiation of immune cells

Inhibitor of binding or differentiation 2 (Id2), a member of helix-loop-helix (HLH) transcriptional factors, is recently reported as an important regulator of the development or differentiation of immune cells. It has been demonstrated that Id2 plays a critical role in the early lymphopoiesis. However, it has been discovered recently that Id2 displays new functions in different immune cells. In the adaptive immune cells, Id2 is required for determining T-cell subsets and B cells. In addition, Id2 is also involved in the development of innate immune cells, including dendritic cells (DCs), natural killer (NK) cells, and other innate lymphoid cells (ILCs). Here, we review the current reports about the role of Id2 in the development or differentiation of main immune cells.

The Id-protein family in developmental and cancer-associated pathways

Inhibitors of DNA binding and cell differentiation (Id) proteins are members of the large family of the helix-loop-helix (HLH) transcription factors, but they lack any DNA-binding motif. During development, the Id proteins play a key role in the regulation of cell-cycle progression and cell differentiation by modulating different cell-cycle regulators both by direct and indirect mechanisms. Several Id-protein interacting partners have been identified thus far, which belong to structurally and functionally unrelated families, including, among others, the class I and II bHLH transcription factors, the retinoblastoma protein and related pocket proteins, the paired-box transcription factors, and the S5a subunit of the 26 S proteasome. Although the HLH domain of the Id proteins is involved in most of their protein-protein interaction events, additional motifs located in their N-terminal and C-terminal regions are required for the recognition of diverse protein partners. The ability of the Id proteins to interact with structurally different proteins is likely to arise from their conformational flexibility: indeed, these proteins contain intrinsically disordered regions that, in the case of the HLH region, undergo folding upon self- or heteroassociation. Besides their crucial role for cell-fate determination and cell-cycle progression during development, other important cellular events have been related to the Id-protein expression in a number of pathologies. Dysregulated Id-protein expression has been associated with tumor growth, vascularization, invasiveness, metastasis, chemoresistance and stemness, as well as with various developmental defects and diseases. Herein we provide an overview on the structural properties, mode of action, biological function and therapeutic potential of these regulatory proteins.

The Id-protein family in developmental and cancer-associated pathways

Inhibitors of DNA binding and cell differentiation (Id) proteins are members of the large family of the helix-loop-helix (HLH) transcription factors, but they lack any DNA-binding motif. During development, the Id proteins play a key role in the regulation of cell-cycle progression and cell differentiation by modulating different cell-cycle regulators both by direct and indirect mechanisms. Several Id-protein interacting partners have been identified thus far, which belong to structurally and functionally unrelated families, including, among others, the class I and II bHLH transcription factors, the retinoblastoma protein and related pocket proteins, the paired-box transcription factors, and the S5a subunit of the 26 S proteasome. Although the HLH domain of the Id proteins is involved in most of their protein-protein interaction events, additional motifs located in their N-terminal and C-terminal regions are required for the recognition of diverse protein partners. The ability of the Id proteins to interact with structurally different proteins is likely to arise from their conformational flexibility: indeed, these proteins contain intrinsically disordered regions that, in the case of the HLH region, undergo folding upon self- or heteroassociation. Besides their crucial role for cell-fate determination and cell-cycle progression during development, other important cellular events have been related to the Id-protein expression in a number of pathologies. Dysregulated Id-protein expression has been associated with tumor growth, vascularization, invasiveness, metastasis, chemoresistance and stemness, as well as with various developmental defects and diseases. Herein we provide an overview on the structural properties, mode of action, biological function and therapeutic potential of these regulatory proteins.

Conservation of Three-Dimensional Helix-Loop-Helix Structure through the Vertebrate Lineage Reopens the Cold Case of Gonadotropin-Releasing Hormone-Associated Peptide

GnRH-associated peptide (GAP) is the C-terminal portion of the gonadotropin-releasing hormone (GnRH) preprohormone. Although it was reported in mammals that GAP may act as a prolactin-inhibiting factor and can be co-secreted with GnRH into the hypophyseal portal blood, GAP has been practically out of the research circuit for about 20 years. Comparative studies highlighted the low conservation of GAP primary amino acid sequences among vertebrates, contributing to consider that this peptide only participates in the folding or carrying process of GnRH. Considering that the three-dimensional (3D) structure of a protein may define its function, the aim of this study was to evaluate if GAP sequences and 3D structures are conserved in the vertebrate lineage. GAP sequences from various vertebrates were retrieved from databases. Analysis of primary amino acid sequence identity and similarity, molecular phylogeny, and prediction of 3D structures were performed. Amino acid sequence comparison and phylogeny analyses confirmed the large variation of GAP sequences throughout vertebrate radiation. In contrast, prediction of the 3D structure revealed a striking conservation of the 3D structure of GAP1 (GAP associated with the hypophysiotropic type 1 GnRH), despite low amino acid sequence conservation. This GAP1 peptide presented a typical helix-loop-helix (HLH) structure in all the vertebrate species analyzed. This HLH structure could also be predicted for GAP2 in some but not all vertebrate species and in none of the GAP3 analyzed. These results allowed us to infer that selective pressures have maintained GAP1 HLH structure throughout the vertebrate lineage. The conservation of the HLH motif, known to confer biological activity to various proteins, suggests that GAP1 peptides may exert some hypophysiotropic biological functions across vertebrate radiation.

Combined Id1 and Id3 Deletion Leads to Severe Erythropoietic Disturbances

The Inhibitor of DNA Binding (Id) proteins play a crucial role in regulating hematopoiesis and are known to interact with E proteins and the bHLH family of transcription factors. Current efforts seek to elucidate the individual roles of Id members in regulating hematopoietic development and specification. However, the nature of their functional redundancies remains elusive since ablation of multiple Id genes is embryonically lethal. We developed a model to test this compensation in the adult. We report that global Id3 ablation with Tie2Cre-mediated conditional ablation of Id1 in both hematopoietic and endothelial cells (Id cDKO) extends viability to 1 year but leads to multi-lineage hematopoietic defects including the emergence of anemia associated with defective erythroid development, a novel phenotype unreported in prior single Id knockout studies. We observe decreased cell counts in the bone marrow and splenomegaly to dimensions beyond what is seen in single Id knockout models. Transcriptional dysregulation of hematopoietic regulators observed in bone marrow cells is also magnified in the spleen. E47 protein levels were elevated in Id cDKO bone marrow cell isolates, but decreased in the erythroid lineage. Chromatin immunoprecipitation (ChIP) studies reveal increased occupancy of E47 and GATA1 at the promoter regions of β-globin and E2A. Bone marrow transplantation studies highlight the importance of intrinsic Id signals in maintaining hematopoietic homeostasis while revealing a strong extrinsic influence in the development of anemia. Together, these findings demonstrate that loss of Id compensation leads to dysregulation of the hematopoietic transcriptional network and multiple defects in erythropoietic development in adult mice.

Phosphorylation Regulates Id2 Degradation and Mediates the Proliferation of Neural Precursor Cells

Inhibitor of DNA binding proteins (Id1-Id4) function to inhibit differentiation and promote proliferation of many different cell types. Among the Id family members, Id2 has been most extensively studied in the central nervous system (CNS). Id2 contributes to cultured neural precursor cell (NPC) proliferation as well as to the proliferation of CNS tumors such as glioblastoma that are likely to arise from NPC-like cells. We identified three phosphorylation sites near the N-terminus of Id2 in NPCs. To interrogate the importance of Id2 phosphorylation, Id2(-/-) NPCs were modified to express wild type (WT) Id2 or an Id2 mutant protein that could not be phosphorylated at the identified sites. We observed that NPCs expressing this mutant lacking phosphorylation near the N-terminus had higher steady-state levels of Id2 when compared to NPCs expressing WT Id2. This elevated level was the result of a longer half-life and reduced proteasome-mediated degradation. Moreover, NPCs expressing constitutively de-phosphorylated Id2 proliferated more rapidly than NPCs expressing WT Id2, a finding consistent with the well-characterized function of Id2 in driving proliferation. Observing that phosphorylation of Id2 modulates the degradation of this important cell-cycle regulator, we sought to identify a phosphatase that would stabilize Id2 enhancing its activity in NPCs and extended our analysis to include human glioblastoma-derived stem cells (GSCs). We found that expression of the phosphatase PP2A altered Id2 levels. Our findings suggest that inhibition of PP2A may be a novel strategy to regulate the proliferation of normal NPCs and malignant GSCs by decreasing Id2 levels. Stem Cells 2016;34:1321-1331.

Effects of upregulation of Id3 in human lung adenocarcinoma cells on proliferation, apoptosis, mobility and tumorigenicity

The inhibitor of DNA-binding/differentiation 3 (Id3) protein is a helix-loop-helix transcription factor and may have an important role in cell proliferation and differentiation. This study was to evaluate the effects of upregulation of Id3 in human lung adenocarcinoma cells on proliferation, apoptosis, mobility and tumorigenicity. Short interference RNA suppression of Id3 (miRId3) in A549 cells was used to investigate the functional role(s) of Id3. Next, we used in vitro wound-healing assay and trans-well assay to study the effects of overexpressed Id3 on migration and invasion of A549 cells. Furthermore, to explore the influence of overexpressed Id3 on in vivo tumorigenesis, adenoviruses containing Id3 gene (Ad-Id3) and empty vector (Ad-LacZ) were generated. Co-transfection of pcDNA/miRId3 and pEGFP/Id3 into A549 cells reversed the Id3-induced cell proliferation inhibition and apoptosis. Upon Id3 transfection, A549 cells displayed decreased migratory and invasive capabilities, however, co-transfection of miRId3 and Id3 into A549 cells reversed the Id3-induced inhibitions of migratory and invasive capabilities. Three groups of nude mice were inoculated with Ad-LacZ, Ad-Id3 transfectants and untransfected A549 cells, respectively. Twenty-eight days after inoculation, tumors induced by Ad-Id3 transfectants grew much more slowly compared with Ad-LacZ transfectants and control group. This study provides for the first time both in vitro and in vivo proofs that forced expression of Id3 in lung adenocarcinoma cells reduces tumor growth rate and may be a potential target for tumor suppression.

Extramacrochaetae functions in dorsal-ventral patterning of Drosophila imaginal discs

One of the seminal events in the history of a tissue is the establishment of the anterior-posterior, dorsal-ventral (D/V) and proximal-distal axes. Axis formation is important for the regional specification of a tissue and allows cells along the different axes to obtain directional and positional information. Within the Drosophila retina, D/V axis formation is essential to ensure that each unit eye first adopts the proper chiral form and then rotates precisely 90° in the correct direction. These two steps are important because the photoreceptor array must be correctly aligned with the neurons of the optic lobe. Defects in chirality and/or ommatidial rotation will lead to disorganization of the photoreceptor array, misalignment of retinal and optic lobe neurons, and loss of visual acuity. Loss of the helix-loop-helix protein Extramacrochaetae (Emc) leads to defects in both ommatidial chirality and rotation. Here, we describe a new role for emc in eye development in patterning the D/V axis. We show that the juxtaposition of dorsal and ventral fated tissue in the eye leads to an enrichment of emc expression at the D/V midline. emc expression at the midline can be eliminated when D/V patterning is disrupted and can be induced in situations in which ectopic boundaries are artificially generated. We also show that emc functions downstream of Notch signaling to maintain the expression of four-jointed along the midline.

The parathyroid hormone-regulated transcriptome in osteocytes: parallel actions with 1,25-dihydroxyvitamin D3 to oppose gene expression changes during differentiation and to promote mature cell function

Although localized to the mineralized matrix of bone, osteocytes are able to respond to systemic factors such as the calciotropic hormones 1,25(OH)2D3 and PTH. In the present studies, we examined the transcriptomic response to PTH in an osteocyte cell model and found that this hormone regulated an extensive panel of genes. Surprisingly, PTH uniquely modulated two cohorts of genes, one that was expressed and associated with the osteoblast to osteocyte transition and the other a cohort that was expressed only in the mature osteocyte. Interestingly, PTH's effects were largely to oppose the expression of differentiation-related genes in the former cohort, while potentiating the expression of osteocyte-specific genes in the latter cohort. A comparison of the transcriptional effects of PTH with those obtained previously with 1,25(OH)2D3 revealed a subset of genes that was strongly overlapping. While 1,25(OH)2D3 potentiated the expression of osteocyte-specific genes similar to that seen with PTH, the overlap between the two hormones was more limited. Additional experiments identified the PKA-activated phospho-CREB (pCREB) cistrome, revealing that while many of the differentiation-related PTH regulated genes were apparent targets of a PKA-mediated signaling pathway, a reduction in pCREB binding at sites associated with osteocyte-specific PTH targets appeared to involve alternative PTH activation pathways. That pCREB binding activities positioned near important hormone-regulated gene cohorts were localized to control regions of genes was reinforced by the presence of epigenetic enhancer signatures exemplified by unique modifications at histones H3 and H4. These studies suggest that both PTH and 1,25(OH)2D3 may play important and perhaps cooperative roles in limiting osteocyte differentiation from its precursors while simultaneously exerting distinct roles in regulating mature osteocyte function. Our results provide new insight into transcription factor-associated mechanisms through which PTH and 1,25(OH)2D3 regulate a plethora of genes important to the osteoblast/osteocyte lineage.

The potential role of inhibitor of differentiation-3 in human adipose tissue remodeling and metabolic health

Metabolic health in obesity is known to differ among individuals, and the distribution of visceral (VAT) and subcutaneous adipose tissue (SAT) plays an important role in this regard. Adipose tissue expansion is dependent on new blood vessel formation in order to prevent hypoxia and inflammation in the tissue. Regulation of angiogenesis in SAT and VAT in response to diet is therefore crucial for the metabolic outcome in obesity. Knowledge about the underlying genetic mechanisms determining metabolic health in obesity is very limited. We aimed to review the literature of the inhibitor of differentiation-3 (ID3) gene in relation to adipose tissue and angiogenesis in humans in order to determine whether ID3 could be involved in the regulation of adipose tissue expansion and metabolic health in human obesity. We find evidence that ID3 is involved in regulatory mechanisms in adipose tissue and regulates angiogenesis in many tissues including adipose tissue. We discuss how this might influence obesity and metabolic health in obesity and further discuss some potential mechanisms by which ID3 might regulate visceral and subcutaneous adipose tissue expansion. The combined results from the reviewed literature suggest ID3 to play a potential role in the underlying regulatory mechanisms of metabolic health in human obesity. The literature is still sparse and further studies focusing on human ID3 in relation to the nature of obesity are warranted.

Id proteins in the vasculature: from molecular biology to cardiopulmonary medicine

The inhibitors of differentiation (Id) proteins belong to the helix-loop-helix group of transcription factors and regulate cell differentiation and proliferation. Recent studies have reported that Id proteins play important roles in cardiogenesis and formation of the vasculature. We have also demonstrated that heritable pulmonary arterial hypertension (HPAH) patients have dysregulated Id gene expression in pulmonary artery smooth muscle cells. The interaction between bone morphogenetic proteins and other growth factors or cytokines regulates Id gene expression, which impacts on pulmonary vascular cell differentiation and proliferation. Exploration of the roles of Id proteins in vascular remodelling that occurs in PAH and atherosclerosis might provide new insights into the molecular basis of these diseases. In addition, current progress in identification of the interactors of Id proteins will further the understanding of the function of Ids in vascular cells and enable the identification of novel targets for therapy in PAH and other cardiovascular diseases.

The ID proteins: master regulators of cancer stem cells and tumour aggressiveness

Inhibitor of DNA binding (ID) proteins are transcriptional regulators that control the timing of cell fate determination and differentiation in stem and progenitor cells during normal development and adult life. ID genes are frequently deregulated in many types of human neoplasms, and they endow cancer cells with biological features that are hijacked from normal stem cells. The ability of ID proteins to function as central 'hubs' for the coordination of multiple cancer hallmarks has established these transcriptional regulators as therapeutic targets and biomarkers in specific types of human tumours.

Id proteins: small molecules, mighty regulators

The family of inhibitor of differentiation (Id) proteins is a group of evolutionarily conserved molecules, which play important regulatory roles in organisms ranging from Drosophila to humans. Id proteins are small polypeptides harboring a helix-loop-helix (HLH) motif, which are best known to mediate dimerization with other basic HLH proteins, primarily E proteins. Because Id proteins do not possess the basic amino acids adjacent to the HLH motif necessary for DNA binding, Id proteins inhibit the function of E protein homodimers, as well as heterodimers between E proteins and tissue-specific bHLH proteins. However, Id proteins have also been shown to have E protein-independent functions. The Id genes are broadly but differentially expressed in a variety of cell types. Transcription of the Id genes is controlled by transcription factors such as C/EBPβ and Egr as well as by signaling pathways triggered by different stimuli, which include bone morphogenic proteins, cytokines, and ligands of T cell receptors. In general, Id proteins are capable of inhibiting the differentiation of progenitors of different cell types, promoting cell-cycle progression, delaying cellular senescence, and facilitating cell migration. These properties of Id proteins enable them to play significant roles in stem cell maintenance, vasculogenesis, tumorigenesis and metastasis, the development of the immune system, and energy metabolism. In this review, we intend to highlight the current understanding of the function of Id proteins and discuss gaps in our knowledge about the mechanisms whereby Id proteins exert their diverse effects in multiple cellular processes.

Structure activity relationships of peptidic analogs of MyoD for the development of Id1 inhibitors as antiproliferative agents

Id proteins, inhibitors of DNA binding proteins, have highly conserved dimerization motif known as the helix-loop-helix (HLH) domain that acts as a negative regulator of basic HLH (bHLH) transcription factors. In signaling pathways, Id proteins play an important role in cellular development, proliferation, and differentiation. The mechanism of Id proteins is to antagonize bHLH proteins, thereby preventing them from binding to DNA and inhibiting transcription of cellular differentiation-associated genes in cancer. Recently, we reported an inhibitor of Id1, peptide 3C, which showed good affinity to Id1 protein and exhibited inhibitory effects in cancer cells. In this study, Ala (A)-substituted analogs of peptide 3C were synthesized by SPPS, purified by RP-HPLC, and characterized by MALDI-TOF MS. Binding of each peptide to Id1 or Id1-HLH (the HLH domain of Id1) was monitored by surface plasmon resonance (SPR)-based biosensor. Biological effect of each peptide in MCF-7 breast cancer cells was analyzed by MTT cell viability assay. The secondary structure of substituted analogs of peptide 3C was investigated by circular dichroism (CD) spectroscopy. SPR results revealed that A-substituted analogs of peptide 3C showed weaker binding to Id1 than that of peptide 3C, indicating that the six amino acid residues in the N-terminal of peptide 3C were all essential for binding to Id1 and the importance of amino acid residue was I(2)  > Q(6)  > Y(1)  > G(4)  > L(5)  > E(3). In addition, substitution of E(3) in peptide 3C with D, Q, and R did not improve the binding potency of peptide 3C. MTT assay demonstrated that neither A-substituted nor position 3-substituted analogs of peptide 3C showed increased antiproliferative effect in MCF-7 cancer cells. CD results indicated that peptide 3C exhibited the highest content of α-helical structure (39.37%), suggesting that the α-helical structure may contribute to its binding potency for Id1 and Id1-HLH. SAR results provided important information for the development of peptidic inhibitors of Id1 as anticancer agents and demonstrated peptide 3C as a promising lead for further modifications.

Cloning, purification and preliminary X-ray data analysis of the human ID2 homodimer

The ID proteins are named for their role as inhibitors of DNA binding and differentiation. They contain a helix-loop-helix (HLH) domain but lack a basic DNA-binding domain. In complex with basic HLH (bHLH) transcription factors, gene expression is regulated by DNA-binding inactivation. Although the HLH domain is highly conserved and shares a similar topology, the IDs preferentially bind class I bHLH-group members such as E47 (TCF3) but not the class III bHLH member Myc. A structure of an ID protein could potentially shed light on its mechanism. Owing to their short half-lives in vivo and reported in vitro instability, this paper describes the strategies that went into expressing sufficient soluble and stable ID2 to finally obtain diffraction-quality crystals. A 2.1 Å resolution data set was collected from a crystal belonging to space group P3(1)21 with unit-cell parameters a=b=51.622, c=111.474 Å, α=β=90, γ=120° that was obtained by hanging-drop vapour diffusion in a precipitant solution consisting of 0.1 M MES pH 6.5, 2.0 M potassium acetate. The solvent content was consistent with the presence of one or two molecules in the asymmetric unit.

A divalent ion is crucial in the structure and dominant-negative function of ID proteins, a class of helix-loop-helix transcription regulators

Inhibitors of DNA binding and differentiation (ID) proteins, a dominant-negative group of helix-loop-helix (HLH) transcription regulators, are well-characterized key players in cellular fate determination during development in mammals as well as Drosophila. Although not oncogenes themselves, their upregulation by various oncogenic proteins (such as Ras, Myc) and their inhibitory effects on cell cycle proteins (such as pRb) hint at their possible roles in tumorigenesis. Furthermore, their potency as inhibitors of cellular differentiation, through their heterodimerization with subsequent inactivation of the ubiquitous E proteins, suggest possible novel roles in engineering induced pluripotent stem cells (iPSCs). We present the high-resolution 2.1Å crystal structure of ID2 (HLH domain), coupled with novel biochemical insights in the presence of a divalent ion, possibly calcium (Ca2+), in the loop of ID proteins, which appear to be crucial for the structure and activity of ID proteins. These new insights will pave the way for new rational drug designs, in addition to current synthetic peptide options, against this potent player in tumorigenesis as well as more efficient ways for stem cells reprogramming.

Early transcriptional pattern of angiogenesis induced by EGCG treatment in cervical tumour cells

The major green tea polyphenol (-)-epigallocatechin-3-gallate (EGCG) has been shown to exhibit antitumour activities in several tumour models. One of the possible mechanisms by which EGCG can inhibit cancer progression is through the modulation of angiogenesis signalling cascade. The tumour cells’ ability to tightly adhere to endothelium is a very important process in the metastatic process, because once disseminated into the bloodstream the tumour cells must re-establish adhesive connections to endothelium in order to extravasate into the target tissues. In this study, we investigated the anti-angiogenic effects of EGCG treatment (10 μM) on human cervical tumour cells (HeLa) by evaluating the changes in the expression pattern of 84 genes known to be involved in the angiogenesis process. Transcriptional analysis revealed 11 genes to be differentially expressed and was further validated by measuring the induced biological effects. Our results show that EGCG treatment not only leads to the down-regulation of genes involved in the stimulation of proliferation, adhesion and motility as well as invasion processes, but also to the up-regulation of several genes known to have antagonist effects. We observed reduced proliferation rates, adhesion and spreading ability as well as invasiveness of HeLa tumour cells upon treatment, which suggest that EGCG might be an important anti-angiogenic therapeutic approach in cervical cancers.

HEB in the spotlight: Transcriptional regulation of T-cell specification, commitment, and developmental plasticity

The development of T cells from multipotent progenitors in the thymus occurs by cascades of interactions between signaling molecules and transcription factors, resulting in the loss of alternative lineage potential and the acquisition of the T-cell functional identity. These processes require Notch signaling and the activity of GATA3, TCF1, Bcl11b, and the E-proteins HEB and E2A. We have shown that HEB factors are required to inhibit the thymic NK cell fate and that HEBAlt allows the passage of T-cell precursors from the DN to DP stage but is insufficient for suppression of the NK cell lineage choice. HEB factors are also required to enforce the death of cells that have not rearranged their TCR genes. The synergistic interactions between Notch1, HEBAlt, HEBCan, GATA3, and TCF1 are presented in a gene network model, and the influence of thymic stromal architecture on lineage choice in the thymus is discussed.

Overexpression of Id3 induces apoptosis of A549 human lung adenocarcinoma cells

OBJECTIVES

Inhibitor of differentiation 3 (Id3) protein has been implicated in the control of multiple cell death signalling pathways and in aetiology of numerous diseases. The aims of this study were to construct a recombinant eukaryotic expression vector (pEGFP/Id3), containing human Id3 (hId3) fused with enhanced green fluorescent protein (EGFP), and to determine effects of ectopic Id3 overexpression, on human lung adenocarcinoma cell (A549) proliferation.

MATERIALS AND METHODS

Human Id3 cDNA was inserted into pEGFP-N1 vector to yield the recombinant eukaryotic expression vector pEGFP/Id3. Cells were transfected with pEGFP or pEGFP/Id3, and proliferation of EGFP-expressing cells was monitored by flow cytometry (FCM) and confocal fluorescence microscopy. RT-PCR, immunoblotting and immunocytochemistry were used to assess Id3 mRNA transcription and protein expression. Apoptosis was evaluated by Annexin V/7-AAD staining and FCM, while nuclear morphology of apoptotic cells was examined using Hoechst 33258 staining.

RESULTS

Over 4 days transfection with pEGFP, the proportion of EGFP-positive A549 cells peaked at approximately 60% by 48 h and remained stable over the next 48 h. In contrast, the proportion of EGFP-positive cells in cultures transfected with pEGFP/Id3 decreased from a peak of 60% at 48 h to <5% at 96 h, suggesting that Id3 expression inhibited cell proliferation or survival. Annexin V/7-AAD and Hoechst 33258 staining revealed significantly higher rates of apoptosis in pEGFP/Id3-transfected cells.

CONCLUSION

Overexpression of Id3 triggered apoptosis in A549 human lung adenocarcinoma cells, implicating Id3 in negative control of tumour growth. These Id3-induced pro-apoptotic signalling pathways require further study, but this preliminary investigation suggests that Id3 regulation could be exploited in anti-tumour therapies.

Smurf2-mediated ubiquitination and degradation of Id1 regulates p16 expression during senescence

The inhibitor of differentiation or DNA binding (Id) family of transcription regulators plays an important role in cell proliferation, differentiation, and senescence. However, regulation of Id expression during these processes is poorly understood. Id proteins are known to undergo rapid turnover mediated by the ubiquitin-proteasome pathway. Anaphase-promoting complex has been shown to ubiquitinate Id2, but E3 ubiquitin ligase(s) that ubiquitinate other Id family members are not known. Here, we report for the first time the identification of Smurf2 as the E3 ligase that ubiquitinates Id1 and Id3. Smurf2-mediated ubiquitination and consequent degradation of Id1 or Id3 plays an important role in the regulation of Id expression in senescent cells. Furthermore, we found that Id1 is the mediator through which Smurf2 regulates p16 expression, providing a mechanistic link between Smurf2 and p16 expression during senescence.

Modeling Sjögren's syndrome with Id3 conditional knockout mice

The Id3 gene has been shown to play important roles in the development and function of broad tissue types including B and T cells. Id3 deficient mice develop autoimmune disease similar to human Sjögren's syndrome. Both B and T lymphocytes have been implicated to contribute to the disease phenotype in this disease model. In order to gain a better understanding of individual cell types in this disease model, we generated an Id3 conditional allele. An LckCre transgene was used to induce Id3 deletion in developing T cells. We showed that the Id3 gene was efficiently disrupted in early thymocyte development prior to T cell receptor (TCR)-mediated positive selection. Consequently, thymocyte maturation was impaired in the conditional knockout mice. These mice developed exocrinopathy starting at two months of age and subsequently exhibited high incidence of lymphocyte infiltration to salivary glands between eight and 12 months of age. This progressive feature of disease development is very similar to those observed in Id3 germline knockout mice. This study establishes a new model for investigating the relationship between T cell development and autoimmune disease. Our observation provides an experimental case that autoimmune disease may be induced by acquired mutation in developing T cells.

Mechanisms of bone morphogenetic protein 2 (BMP2) stimulated inhibitor of DNA binding 3 (Id3) transcription

Bone morphogenetic protein 2 (BMP2) stimulates expression of the inhibitors of DNA binding (Id) 1, 2, and 3 in a variety of cell types. Here, we examined mechanisms mediating BMP2-stimulated Id3 transcription in murine gonadotropes. Using a combination of quantitative RT-PCR, promoter-reporter analyses, over-expression, and RNA interference approaches, we demonstrate that BMP2 signals via the BMPR2 and BMPR1A (ALK3) receptors and intracellular signaling proteins SMADs 1 and 5 to stimulate Id3 transcription. We further define a novel 6-bp cis-element mediating BMP2- and SMAD-dependent transcription, though this site does not appear to bind SMADs directly. A specific DNA binding protein complex binds to this element, but its constituent protein(s) remain undetermined. Recently, a more distal enhancer was shown to mediate BMP4-induction of the human ID3 gene in ovarian cancer cells. This enhancer is conserved in the murine gene and we demonstrate its role in BMP2-induced Id3 promoter activity in gonadotropes. Conversely, the proximal cis-element defined here is also conserved in human ID3 and we demonstrate its functional role in BMP2-induction of ID3 transcription. Finally, we show that the two regulatory elements also mediate BMP2-induction of Id3 promoter activity in murine fibroblasts. Collectively, we have defined a general mechanism whereby BMP2 regulates Id3/ID3 transcription in different cell types and in different species.

Cell cycle regulation during proliferation and differentiation of mammalian muscle precursor cells

Proliferation and differentiation of muscle precursor cells are intensively studied not only in the developing mouse embryo but also using models of skeletal muscle regeneration or analyzing in vitro cultured cells. These analyses allowed to show the universality of the cell cycle regulation and also uncovered tissue-specific interplay between major cell cycle regulators and factors crucial for the myogenic differentiation. Examination of the events accompanying proliferation and differentiation leading to the formation of functional skeletal muscle fibers allows understanding the molecular basis not only of myogenesis but also of skeletal muscle regeneration. This chapter presents the basis of the cell cycle regulation in proliferating and differentiating muscle precursor cells during development and after muscle injury. It focuses at major cell cycle regulators, myogenic factors, and extracellular environment impacting on the skeletal muscle.

Id1 has a physiological role in regulating early B lymphopoiesis

Basic helix-loop-helix E proteins play critical roles in B-cell development by stimulating B cell-specific gene expression and immunoglobulin gene rearrangement. The function of E proteins can be effectively suppressed by their naturally occurring inhibitors, Id1 to 4. Ectopic expression of Id1 has been shown to block B-cell development at the early pro-B cell stage. However, whether Id1 plays a physiological role in controlling B lymphopoiesis was not known. Although Id1-deficient mice do not exhibit significant abnormalities in steady-state B lymphopoiesis, we detected more robust B-cell engraftment in transplant recipients of Id1-deficient bone marrow compared to those of wild-type donor cells. In culture, Id1 ablation dramatically enhances B-lineage cell production without any marked effects on myeloid differentiation. Consistently, Id1 expression was found in pro-B but not pre-B cells as measured by enhanced green fluorescent protein (EGFP) fluorescence and by quantitative reverse transcription-PCR. Although loss of Id1 did not alter the number of B-cell colonies generated from whole bone marrow or the proliferation rate of developing B cells, B-cell colonies were detectable at a much earlier time point and the size of the colonies were larger. Therefore, we infer that Id1-deficient progenitors possess higher potential to differentiate to the pre-B cell stage when a proliferative burst occurs. Taken together, we present evidence to suggest that Id1 plays a physiological role in restraining the developmental progression, which may be important for proper B-cell differentiation in the bone marrow.

Mutation of inhibitory helix-loop-helix protein Id3 causes γδ T-cell lymphoma in mice

Human γδ T-cell lymphoma is a rare clinicopathologic entity with aggressive course and poor prognosis. The etiology and pathogenesis of γδ T-cell lymphoma is unknown. We show here that mice with deficiency in inhibitory helix-loop-helix protein Id3 (Id3(-/-)) developed γδ T-cell lymphoma that resembled human γδ T-cell lymphoma. The Id3(-/-) mice with lymphoma showed splenomegaly, hepatomegaly, and lymphadenopathy with involvement of bone marrow, thymus, kidney, and lungs between 6 and 15 months of age. Phenotypic analysis revealed that lymphomatous cells were cluster of differentiation (CD)3(+), γδ T-cell receptor (TCR)(+), and αβ TCR(-), and expressed CD8(+)CD4(-), CD4(+)CD8(-), or a mixture of the two. Id3(-/-) γδ T-cell lymphoma used predominantly Vγ1.1, some Vγ3, yet no Vγ2 TCR, and some showed increased levels of the oncogene c-Myc. Strikingly, adoptive transfer of the γδ T-cell lymphoma into syngeneic Rag1(-/-) mice resulted in aggressive γδ T-cell lymphoma, identical to the Id3(-/-) donor. Thus, our data demonstrate that Id3 regulates the development of γδ T-cell lymphoma in mice, raising a possibility of Id3 gene mutation in human γδ T-cell lymphoma. Our model will provide a tool for studying the molecular mechanisms and development of human γδ T-cell lymphoma.

Affinity of synthetic peptide fragments of MyoD for Id1 protein and their biological effects in several cancer cells

MyoD is a DNA-binding protein capable of specific interactions that involve the helix-loop-helix (HLH) domain. The HLH motif of MyoD can form oligomers with the HLH motif of Id1 (the inhibitor of DNA-binding proteins) that folds into a highly stable helical conformation stabilized by the self-association. The Id family consists of four related proteins that contain a highly conserved dimerization motif known as the HLH domain. In signaling pathways, Id proteins act as dominant negative antagonists of the basic helix-loop-helix (bHLH) family of transcription factors which play important roles in cellular development, proliferation, and differentiation. The mechanism of Id proteins is to antagonize bHLH proteins by binding as dominant negative HLH proteins to form high-affinity heterodimers with other bHLH proteins, thereby preventing them from binding to DNA and inhibiting transcription of differentiation-associated genes. The goal of this study is to design and synthesize peptide fragments of MyoD with high affinity for Id1 to interrupt the interactions among Id1, MyoD, and other bHLH DNA-binding proteins and to inhibit the proliferation of cancer cells. Affinity of each peptide for Id1 was determined by surface plasmon resonance (SPR) technology. The secondary structure of each peptide was studied by circular dichroism (CD) spectroscopy. Biological effects of each peptide in several cancer cells such as breast and colon cancer cells were analyzed. Results demonstrated that the peptide 3C (H-Tyr-Ile-Glu-Gly-Leu-Gln-Ala-Leu-Leu-Arg-Asp-Gln-NH(2)) not only showed high affinity for Id1 but also exhibited antiproliferative effects in HT-29 and MCF-7 cancer cells; the IC(50) value of 3C was determined as 25 microM in both cells. The percentage of sub-G1 in the cell cycle of the cancer cells treated with 5 microM of 3C was increased, indicating the induced apoptosis of cancer cells by 3C. Taken together, the peptide 3C is a promising lead compound for the development of antiproliferative agents.

Impaired terminal differentiation of hippocampal granule neurons and defective contextual memory in PC3/Tis21 knockout mice

Neurogenesis in the dentate gyrus of the adult hippocampus has been implicated in neural plasticity and memory, but the molecular mechanisms controlling the proliferation and differentiation of newborn neurons and their integration into the synaptic circuitry are still largely unknown. To investigate this issue, we have analyzed the adult hippocampal neurogenesis in a PC3/Tis21-null mouse model. PC3/Tis21 is a transcriptional co-factor endowed with antiproliferative and prodifferentiative properties; indeed, its upregulation in neural progenitors has been shown to induce exit from cell cycle and differentiation. We demonstrate here that the deletion of PC3/Tis21 causes an increased proliferation of progenitor cells in the adult dentate gyrus and an arrest of their terminal differentiation. In fact, in the PC3/Tis21-null hippocampus postmitotic undifferentiated neurons accumulated, while the number of terminally differentiated neurons decreased of 40%. As a result, PC3/Tis21-null mice displayed a deficit of contextual memory. Notably, we observed that PC3/Tis21 can associate to the promoter of Id3, an inhibitor of proneural gene activity, and negatively regulates its expression, indicating that PC3/Tis21 acts upstream of Id3. Our results identify PC3/Tis21 as a gene required in the control of proliferation and terminal differentiation of newborn neurons during adult hippocampal neurogenesis and suggest its involvement in the formation of contextual memories.

PDCA expression by B lymphocytes reveals important functional attributes

We have demonstrated in this study the existence of a PDCA-expressing functional B cell population (PDCA+ B lymphocytes), which differentiates from activated conventional B (PDCA-IgM+) lymphocytes. Stimulation with anti-micro, LPS, CpG oligodeoxynucleotide, HSV-1, or CTLA-4 Ig activates the PDCA+ B lymphocytes, leading to cell division and induction of type I IFNs and IDO. Notably, the PDCA+ B lymphocytes are capable of Ag-specific Ab production and Ig class switching, which is corroborated by transfer experiments in B- and PDCA+ B lymphocyte-deficient microMT mice. Importantly, in lupus-prone MRL-Fas(lpr) mice, PDCA+ B lymphocytes remain the principal source of autoantibodies. The PDCA+ B lymphocytes have phenotypes with plasmacytoid dendritic cells, but are a distinct cell population in that they develop from C-kit+B220+ pro-B precursors. Thus, our data suggest that not all PDCA+ cells are dendritic cell-derived plasmacytoid dendritic cells and that a significant majority is the PDCA+ B lymphocyte population having distinct phenotype and function.

Follicle-stimulating hormone (FSH) transiently blocks FSH receptor transcription by increasing inhibitor of deoxyribonucleic acid binding/differentiation-2 and decreasing upstream stimulatory factor expression in rat Sertoli cells

FSH acts through the FSH receptor (FSHR) to modulate cell processes that are required to support developing spermatozoa. Within the testis, only Sertoli cells possess receptors for FSH and are the major targets for this regulator of spermatogenesis. FSH stimulation of Sertoli cells for 24-48 h is known to induce Fshr mRNA expression through an E-box motif (CACGTG) located 25 bp upstream of the transcription start site. In contrast, FSH stimulation for 8 h inhibits Fshr transcription. DNA-protein binding studies performed using nuclear extracts from Sertoli cells show that protein binding to the Fshr promoter E-box was reduced 68% after 6 h of FSH stimulation but increased 191% over basal levels after 48 h of stimulation. The proteins binding to the Fshr E-box were identified as upstream stimulatory factor (USF)-1 and -2. FSH stimulation transiently decreased USF1 levels and increased the expression of the inhibitor of DNA binding/differentiation (ID)-2 repressor protein with the same kinetics as the decreased USF/E-box interactions. Overexpression of ID2 resulted in a dose-dependent decrease in USF-driven Fshr promoter activity in the MSC-1 Sertoli cell line, and ID2 inhibited USF binding to the Fshr E-box. Together, these studies suggest that stimulation of Sertoli cells with FSH transiently decreases expression of the USF1 activator and induces accumulation of the ID2 repressor, to block USF binding to the Fshr promoter and delay activation of Fshr transcription. This FSH-regulated mechanism may explain the cyclical changes in Fshr expression that occurs in Sertoli cells in vivo.

Inhibitors of Differentiation/DNA Binding Proteins Id1 and Id3 Are Regulated by Statins in Endothelial Cells

Id proteins (inhibitors of differentiation), which are involved in the control of cell cycle progression, can delay cellular differentiation and senescence and have been implicated in angiogenesis. The regulation of Id proteins in endothelial cells (ECs) by proangiogenic statins has not been investigated yet and remains unresolved. In this study, human dermal microvascular ECs (HDMECs) were stimulated with fluvastatin, vascular endothelial growth factor (VEGF), hepatocyte growth factor (HGF), and serum in vitro. The regulation of Id1, Id3, p21, p27, and p53 and the phosphorylation of AKT was investigated by Western blotting. Id1 was up-regulated by fluvastatin and serum, but not by VEGF and HGF. Fluvastatin did not regulate p21 and p27, but down-regulated Id3 and p53 slightly. In contrast to VEGF and HGF, fluvastatin did not result in AKT phosphorylation, indicating that this pathway is not involved in the control of endothelial Id1 expression. These experiments demonstrate for the first time that Id1 can be up-regulated and p53 down-regulated by a statin in HDMECs. Regulation of these proteins in ECs may account for the proangiogenic effect of statins.

USF1/2 transcription factor DNA-binding activity is induced during rat Sertoli cell differentiation

Each Sertoli cell can support a finite number of developing germ cells. During development of the testis, the cessation of Sertoli cell proliferation and the onset of differentiation determine the final number of Sertoli cells and, hence, the number of sperm that can be produced. We hypothesize that the transition from proliferation to differentiation is facilitated by E-box transcription factors that induce the expression of differentiation-promoting genes. The relative activities of E-box proteins were studied in primary Sertoli cells isolated from 5-, 11-, and 20-day-old rats, representing proliferating, differentiating, and differentiated cells, respectively. E-box DNA-binding activity is almost undetectable 5 days after birth but peaks with initiation of differentiation 11 days after birth and remains elevated. Upstream stimulatory factors 1 and 2 (USF1 and USF2) were found to be the predominant E-box proteins present within DNA-protein complexes formed after incubating E-box-containing probes with nuclear extracts from developing Sertoli cells. The known potentiator of Sertoli cell differentiation, thyroxine, increases USF DNA-binding activity in Sertoli cells before differentiation (5-day-old Sertoli cells) but not after differentiation is initiated (11- and 20-day-old Sertoli cells). The developmental-specific increase in USF1 and USF2 DNA-binding activity may facilitate the switch from proliferation to differentiation and, thus, determine the ultimate number of Sertoli cells present within the testes and the upper limit of fertility.

Id1 is a common downstream target of oncogenic tyrosine kinases in leukemic cells

Oncogenic tyrosine kinases, such as BCR-ABL, TEL-ABL, TEL-PDGFbetaR, and FLT3-ITD, play a major role in the development of hematopoietic malignancy. They activate many of the same signal transduction pathways. To identify the critical target genes required for transformation in hematopoietic cells, we used a comparative gene expression strategy in which selective small molecules were applied to 32Dcl3 cells that had been transformed to factor-independent growth by these respective oncogenic alleles. We identified inhibitor of DNA binding 1 (Id1), a gene involved in development, cell cycle, and tumorigenesis, as a common target of these oncogenic kinases. These findings were prospectively confirmed in cell lines and primary bone marrow cells engineered to express the respective tyrosine kinase alleles and were also confirmed in vivo in murine models of disease. Moreover, human AML cell lines Molm-14 and K562, which express the FLT3-ITD and BCR-ABL tyrosine kinases, respectively, showed high levels of Id1 expression. Antisense and siRNA based knockdown of Id1-inhibited growth of these cells associated with increased p27(Kip1) expression and increased sensitivity to Trail-induced apoptosis. These findings indicate that Id1 is an important target of constitutively activated tyrosine kinases and may be a therapeutic target for leukemias associated with oncogenic tyrosine kinases.

Is Inhibitor of differentiation 3 involved in human primary Sjögren's syndrome?

OBJECTIVES

Inhibitor of differentiation 3 (Id3)-deficient mice show sicca symptoms, lymphocyte infiltration of exocrine glands and positive anti-Ro/SSA and anti-La/SSB antibodies, all hallmarks of primary Sjögren's syndrome (pSS). The impairment of Id3 in T cells and, possibly, in salivary glandular epithelial cells (SGECs) seems to be involved. This animal model prompted us to investigate the role of Id3 in human pSS.

METHODS

Quantitative Id3 expression in peripheral T cells, cultured SGECs and in total minor salivary glands was assessed by RT-PCR in pSS patients and controls. After Id3 sequencing, we investigated two single nucleotide polymorphisms (SNPs) (c.313G>A and g.-156A>G) in a case-control study of 212 Caucasian pSS patients and 168 controls.

RESULTS

Quantitative Id3 expression was not decreased in pSS patients nor in SGECs, in T cells or in minor salivary glands. As well, patients and controls did not differ in allele and genotype frequencies of Id3 SNPs (P = 0.67 and P = 0.71 for the c.313G>A and the g.-156A>G, respectively). Neither SNP was associated with a pattern of autoantibody secretion.

CONCLUSION

Although the Id3-deficient mouse model represents an attractive model for human pSS, Id3 expression is not impaired in SGECs, peripheral T cells and in labial salivary glands in pSS patients and Id3-relevant SNPs do not give evidence of genetic predisposition in Caucasian pSS patients.