TRAF5 promotes plasmacytoid dendritic cell development from bone marrow progenitors.

The conventional dendritic cells (cDCs) and plasmacytoid DCs (pDCs) originate from the same common dendritic cell precursor cells in the bone marrow. The pDCs produce large amounts of type 1 interferon in response to foreign nucleic acid and crucially contribute to host defense against viral infection. Tumor necrosis factor (TNF) receptor-associated factor 5 (TRAF5) is a pivotal component of various TNF receptor signaling pathways in the immune system. Although the functions of TRAF5 in T and B lymphocytes have been well studied, its roles in pDCs remains to be fully elucidated. In this study, we show that the expression of TRAF5 supports the generation of pDCs in the bone marrow and also critically contributes to the homeostasis of the pDC subset in the periphery in a cell-intrinsic manner. Furthermore, we provide evidence that TRAF5 promotes the commitment of DC precursor cells toward pDC versus cDC subsets, which is regulated by the balance of transcription factors TCF4 and ID2. Together our findings reveal that TRAF5 acts as a positive regulator of pDC differentiation from bone marrow progenitors.

BMP4 promotes mouse iPS cell differentiation to male germ cells via Smad1/5, Gata4, Id1 and Id2.

Generation of male germ cells from pluripotent cells could provide male gametes for treating male infertility and offer an ideal model for unveiling molecular mechanisms of spermatogenesis. However, the influence and exact molecular mechanisms, especially downstream effectors of BMP4 signaling pathways, in male germ cell differentiation of the induce pluripotent stem (iPS) cells, remain unknown. This study was designed to explore the role and mechanism of BMP4 signaling in the differentiation of mouse iPS cells to male germ cells. Embryoid body (EB) formation and recombinant BMP4 or Noggin were utilized to evaluate the effect of BMP4 on male germ cell generation from mouse iPS cells. Germ cell-specific genes and proteins as well as the downstream effectors of BMP4 signaling pathway were assessed using real-time PCR and Western blots. We found that BMP4 ligand and its multiple receptors, including BMPR1a, BMPR1b and BMPR2, were expressed in mouse iPS cells. Real-time PCR and Western blots revealed that BMP4 could upregulate the levels of genes and proteins for germ cell markers in iPS cells-derived EBs, whereas Noggin decreased their expression in these cells. Moreover, Smad1/5 phosphorylation, Gata4 transcription and the transcripts of Id1 and Id2 were enhanced by BMP4 but decreased when exposed to Noggin. Collectively, these results suggest that BMP4 promotes the generation of male germ cells from iPS cells via Smad1/5 pathway and the activation of Gata4, Id1 and Id2 This study thus offers novel insights into molecular mechanisms underlying male germ cell development.

The helix-loop-helix protein id1 controls stem cell proliferation during regenerative neurogenesis in the adult zebrafish telencephalon.

The teleost brain has the remarkable ability to generate new neurons and to repair injuries during adult life stages. Maintaining life-long neurogenesis requires careful management of neural stem cell pools. In a genome-wide expression screen for transcription regulators, the id1 gene, encoding a negative regulator of E-proteins, was found to be upregulated in response to injury. id1 expression was mapped to quiescent type I neural stem cells in the adult telencephalic stem cell niche. Gain and loss of id1 function in vivo demonstrated that Id1 promotes stem cell quiescence. The increased id1 expression observed in neural stem cells in response to injury appeared independent of inflammatory signals, suggesting multiple antagonistic pathways in the regulation of reactive neurogenesis. Together, we propose that Id1 acts to maintain the neural stem cell pool by counteracting neurogenesis-promoting signals.

Id3 and Id2 act as a dual safety mechanism in regulating the development and population size of innate-like γδ T cells.

The innate-like T cells expressing Vγ1.1 and Vδ6.3 represent a unique T cell lineage sharing features with both the γδ T and the invariant NKT cells. The population size of Vγ1.1(+)Vδ6.3(+) T cells is tightly controlled and usually contributes to a very small proportion of thymic output, but the underlying mechanism remains enigmatic. Deletion of Id3, an inhibitor of E protein transcription factors, can induce an expansion of the Vγ1.1(+)Vδ6.3(+) T cell population. This phenotype is much stronger on the C57BL/6 background than on the 129/sv background. Using quantitative trait linkage analysis, we identified Id2, a homolog of Id3, to be the major modifier of Id3 in limiting Vγ1.1(+)Vδ6.3(+) T cell expansion. The Vγ1.1(+)Vδ6.3(+) phenotype is attributed to an intrinsic weakness of Id2 transcription from Id2 C57BL/6 allele, leading to an overall reduced dosage of Id proteins. However, complete removal of both Id2 and Id3 genes in developing T cells suppressed the expansion of Vγ1.1(+)Vδ6.3(+) T cells because of decreased proliferation and increased cell death. We showed that conditional knockout of Id2 alone is sufficient to promote a moderate expansion of γδ T cells. These regulatory effects of Id2 and Id3 on Vγ1.1(+)Vδ6.3(+) T cells are mediated by titration of E protein activity, because removing one or more copies of E protein genes can restore Vγ1.1(+)Vδ6.3(+) T cell expansion in Id2 and Id3 double conditional knockout mice. Our data indicated that Id2 and Id3 collaboratively control survival and expansion of the γδ lineage through modulating a proper threshold of E proteins.

Id2 expression delineates differential checkpoints in the genetic program of CD8α+ and CD103+ dendritic cell lineages.

Dendritic cells (DCs) have critical roles in the induction of the adaptive immune response. The transcription factors Id2, Batf3 and Irf-8 are required for many aspects of murine DC differentiation including development of CD8α(+) and CD103(+) DCs. How they regulate DC subset specification is not completely understood. Using an Id2-GFP reporter system, we show that Id2 is broadly expressed in all cDC subsets with the highest expression in CD103(+) and CD8α(+) lineages. Notably, CD103(+) DCs were the only DC able to constitutively cross-present cell-associated antigens in vitro. Irf-8 deficiency affected loss of development of virtually all conventional DCs (cDCs) while Batf3 deficiency resulted in the development of Sirp-α(-) DCs that had impaired survival. Exposure to GM-CSF during differentiation induced expression of CD103 in Id2-GFP(+) DCs. It did not restore cross-presenting capacity to Batf3(-/-) or CD103(-)Sirp-α(-)DCs in vitro. Thus, Irf-8 and Batf3 regulate distinct stages in DC differentiation during the development of cDCs. Genetic mapping DC subset differentiation using Id2-GFP may have broad implications in understanding the interplay of DC subsets during protective and pathological immune responses.

CD8α+ DCs can be induced in the absence of transcription factors Id2, Nfil3, and Batf3.

Antiviral immunity and cross-presentation is mediated constitutively through CD8α+ and CD103+ DCs. Development of these DC subsets is thought to require the transcription factors Irf8, Id2, Nfil3, and Batf3, although how this network is regulated is poorly defined. We addressed the nature of the differentiation blocks observed in the absence of these factors and found that although all 4 factors are required for CD103+ DC development, only Irf8 is essential for CD8α+ DCs. CD8α+ DCs emerged in the absence of Id2, Nfil3 and Batf3 in short-term bone marrow reconstitution. These "induced" CD8α+ DCs exhibit several hallmarks of classic CD8α+ DCs including the expression of CD24, Tlr3, Xcr1, Clec9A, and the capacity to cross-present soluble, cell-associated antigens and viral antigens even in the absence of Batf3. Collectively, these results uncover a previously undescribed pathway by which CD8α+ DCs emerge independent of Id2, Nfil3, and Batf3, but dependent on Irf8.

Essential functions for ID proteins at multiple checkpoints in invariant NKT cell development.

Invariant NKT (iNKT) cells display characteristics of both adaptive and innate lymphoid cells (ILCs). Like other ILCs, iNKT cells constitutively express ID proteins, which antagonize the E protein transcription factors that are essential for adaptive lymphocyte development. However, unlike ILCs, ID2 is not essential for thymic iNKT cell development. In this study, we demonstrated that ID2 and ID3 redundantly promoted iNKT cell lineage specification involving the induction of the signature transcription factor PLZF and that ID3 was critical for development of TBET-dependent NKT1 cells. In contrast, both ID2 and ID3 limited iNKT cell numbers by enforcing the postselection checkpoint in conventional thymocytes. Therefore, iNKT cells show both adaptive and innate-like requirements for ID proteins at distinct checkpoints during iNKT cell development.

Id2 influences differentiation of killer cell lectin-like receptor G1(hi) short-lived CD8+ effector T cells.

CD8(+) T cells play a crucial role in the clearance of intracellular pathogens through the generation of cytotoxic effector cells that eliminate infected cells and long-lived memory cells that provide enhanced protection against reinfection. We have previously shown that the inhibitor of E protein transcription factors, Id2, is necessary for accumulation of effector and memory CD8(+) T cells during infection. In this study, we show that CD8(+) T cells lacking Id2 did not generate a robust terminally differentiated killer cell lectin-like receptor G1 (KLRG1)(hi) effector population, but displayed a cell-surface phenotype and cytokine profile consistent with memory precursors, raising the question as to whether loss of Id2 impairs the differentiation and/or survival of effector memory cells. We found that deletion of Bim rescued Id2-deficient CD8(+) cell survival during infection. However, the dramatic reduction in KLRG1(hi) cells caused by loss of Id2 remained in the absence of Bim, such that Id2/Bim double-deficient cells form an exclusively KLRG1(lo)CD127(hi) memory precursor population. Thus, we describe a role for Id2 in both the survival and differentiation of normal CD8(+) effector and memory populations.

Batf3 and Id2 have a synergistic effect on Irf8-directed classical CD8α+ dendritic cell development.

Dendritic cells (DCs) are heterogeneous cell populations represented by different subtypes, each varying in terms of gene expression patterns and specific functions. Recent studies identified transcription factors essential for the development of different DC subtypes, yet molecular mechanisms for the developmental program and functions remain poorly understood. In this study, we developed and characterized a mouse DC progenitor-like cell line, designated DC9, from Irf8(-/-) bone marrow cells as a model for DC development and function. Expression of Irf8 in DC9 cells led to plasmacytoid DCs and CD8α(+) DC-like cells, with a concomitant increase in plasmacytoid DC- and CD8α(+) DC-specific gene transcripts and induction of type I IFNs and IL12p40 following TLR ligand stimulation. Irf8 expression in DC9 cells led to an increase in Id2 and Batf3 transcript levels, transcription factors shown to be important for the development of CD8α(+) DCs. We show that, without Irf8, expression of Id2 and Batf3 was not sufficient for directing classical CD8α(+) DC development. When coexpressed with Irf8, Batf3 and Id2 had a synergistic effect on classical CD8α(+) DC development. We demonstrate that Irf8 is upstream of Batf3 and Id2 in the classical CD8α(+) DC developmental program and define the hierarchical relationship of transcription factors important for classical CD8α(+) DC development.

In vivo genome-wide binding of Id2 to E2F4 target genes as part of a reversible program in mice liver.

The inhibitor of differentiation Id2, a protein lacking the basic DNA-binding domain, is involved in the modulation of a number of biological processes. The molecular mechanisms explaining Id2 pleiotropic functions are poorly understood. Id2 and E2F4 are known to bind simultaneously to c-myc promoter. To study whether Id2 plays a global role on transcriptional regulation, we performed in vivo genome-wide ChIP/chip experiments for Id2 and E2F4 in adult mouse liver. An Id2-containing complex was bound to a common sequence downstream from the TSS on a subset of 442 E2F4 target genes mainly related to cell development and chromatin structure. We found a positive correlation between Id2 protein levels and the expression of E2F4/Id2 targets in fetal and adult liver. Id2 protein stability increased in fetal liver by interaction with USP1 de-ubiquitinating enzyme, which was induced during development. In adult liver, USP1 and Id2 levels dramatically decreased. In differentiated liver tissue, when Id2 concentration was low, E2F4/Id2 was bound to the same region as paused Pol II and target genes remained transcriptionally inactive. Conversely, in fetal liver when Id2 levels were increased, Id2 and Pol II were released from gene promoters and target genes up-regulated. During liver regeneration after partial hepatectomy, we obtained the same results as in fetal liver. Our results suggest that Id2 might be part of a reversible development-related program involved in the paused-ON/OFF state of Pol II on selected genes that would remain responsive to specific stimuli.

Id2, Id3 and Id4 overcome a Smad7-mediated block in tumorigenesis, generating TGF-ß-independent melanoma.

The role for the inhibitors of differentiation (Ids) proteins in melanomagenesis has been poorly explored. In other cell types, Ids have been shown to contribute to cell proliferation, migration and angiogenesis and, along with a number of other genes, are direct downstream targets of the transforming growth factor (TGF)-ß pathway. Expression of Smad7, which suppress TGF-ß signaling, or synthetic TGF-ß inhibitors, was shown to potently suppress melanomagenesis. We found that endogenous Id2, Id3 and Id4 expression was elevated in 1205Lu versus 1205Lu cells constitutively expressing Smad7, indicating Ids may play a role in melanomagenesis. Therefore, the effects of Tet-inducible expression of Id2, Id3 or Id4 along with Smad7 in TGF-ß-dependent 1205Lu human melanoma cells were explored in vitro and in vivo. 1205Lu cells formed subcutaneous tumors in athymic mice, whereas cells expressing Smad7 failed to form tumors. However, 1205Lu cells expressing Smad7 along with doxycycline-induced Id2, Id3 or Id4 were able to overcome the potent tumorigenic block mediated by S7, to varying degrees. Conversely, Id small interfering RNA knockdown suppressed anchorage-independent growth of melanoma. Histology of tumors from 1205Lu cells expressing Smad7 + Id4 revealed an average of 31% necrosis, compared with 5.2% in tumors from 1205Lu with vector only. Downstream, Ids suppressed cyclin-dependent kinase inhibitors, and re-upregulated invasion and metastasis-related genes matrix metalloproteinase 2 (MMP2), MMP9, CXCR4 and osteopontin, shown previously to be downregulated in response to Smad7. This study shows that Id2, Id3 and Id4 are each able to overcome TGF-ß dependence, and establish a role for Ids as key mediators of TGF-ß melanomagenesis.

HIF-1α is a negative regulator of plasmacytoid DC development in vitro and in vivo.

Hypoxia-inducible factors (HIFs) regulate hematopoiesis in the embryo and maintain hematopoietic stem cell function in the adult. How hypoxia and HIFs contribute to hematopoietic lineage differentiation in the adult is ill defined. Here we provide evidence that HIF-1 limits differentiation of precursors into plasmacytoid dendritic cells (pDCs). Low oxygen up-regulated inhibitor of DNA binding 2 (ID2) and suppressed Flt3-L-induced differentiation of bone marrow cells to pDCs in wild-type but not HIF-1α(fl/fl) LysM-Cre bone marrow cells. Moreover, pDC differentiated normally in hypoxic ID2(-/-) bone marrow cultures. Finally, we observed elevated pDC frequencies in bone marrow, blood, and spleen of HIF-1α(fl/fl) LysM-Cre and ID2(-/-), but not HIF-2α(fl/fl) LysM-Cre mice. Our data indicate that the low oxygen content in the bone marrow might limit pDC development. This might be an environmental mechanism to restrict the numbers of these potentially autoreactive cells.

Transcriptional regulator Id2 is required for the CD4 T cell immune response in the development of experimental autoimmune encephalomyelitis.

An effective immune response to Ag challenge is critically dependent on the size of the effector cell population generated from clonal activation of Ag-specific T cells. The transcription network involved in regulating the size of the effector population, particularly for CD4 Th cells, is poorly understood. In this study, we investigate the role of Id2, an inhibitor of E protein transcription factors, in the generation of CD4 effectors. Using a T cell-specific conditional Id2 knockout mouse model, we show that inhibitor of DNA binding (Id)2 is essential for the development of experimental autoimmune encephalomyelitis. Although Ag-specific and IL-17-producing CD4 T cells are produced in these mice, the activated CD4 T cells form a smaller pool of effector cells in the peripheral lymphoid organs, exhibit reduced proliferation and increased cell death, and are largely absent in the CNS. In the absence of Id2, E protein targets, including the proapoptotic protein Bim and SOCS3, are expressed at higher levels among activated CD4 T cells. This study reveals a critical role of Id2 in the control of effector CD4 T cell population size and the development of a Th17-mediated autoimmune disease.

Runx1/Cbfß2 complexes are required for lymphoid tissue inducer cell differentiation at two developmental stages.

Hematopoietic lymphoid tissue inducer (LTi) cells are essential for the development of secondary lymphoid tissues including lymph nodes and Peyer's patches. Two transcription factors, the helix-loop-helix inhibitor Id2 and the retinoic acid-related orphan receptor γt (Rorγt), have been shown to be crucial for LTi cell development. However, it remains unclear how the specification of multipotent hematopoietic progenitor cells toward the LTi lineage is programmed. In this study, we report impaired lymphoid tissue organogenesis in mice in which the function of Runx1/Cbfß transcription factor complexes was attenuated by the loss of either the distal promoter-derived Runx1 or Cbfß2 variant protein. We found that LTi progenitors in fetal liver, defined previously as a lineage marker-negative α4ß7 integrin (α4ß7)(+) IL-7R α-chain (IL-7Rα)(+) population, can be subdivided into Rorγt-expressing IL-7Rα(high) cells and nonexpressing IL-7Rα(mid) cells. Whereas Id2 and Rorγt are required to direct α4ß7(+)IL-7Rα(mid) cells to become α4ß7(+)IL-7Rα(high) cells, Runx1/Cbfß2 complexes are necessary for the emergence of α4ß7(+)IL-7Rα(mid) cells. In addition, the loss of Cbfß2, but not P1-Runx1, resulted in an inefficient upregulation of Rorγt in residual α4ß7(+)IL-7Rα(+) LTi cells at anlagen. Our results thus revealed that Runx1/Cbfß2 complexes regulate the differentiation of LTi cells at two stages: an early specification of hematopoietic progenitors toward the LTi lineage and a subsequent activation of Rorγt expression at anlagen.

ID2: A negative transcription factor regulating oligodendroglia differentiation.

Remyelination of the central nervous system in multiple sclerosis patients is often incomplete. Remyelination depends on normal oligodendrogenesis and the differentiation of oligodendrocyte precursor cells (OPC) into mature oligodendrocytes (OL). Inhibitor of DNA binding (ID), a transcription factor, is thought to inhibit oligodendrogenesis and the differentiation of OPC. This Mini-Review aims to reveal the roles of and mechanisms used by IDs (mainly ID2) in this process. An interaction between ID2 and retinoblastoma tumor suppressor is responsible for the cell cycle transition from G1 to S. The translocation of ID2 between the nucleus and cytoplasm is regulated by E47 and OLIG. An interaction between ID2 and OLIG mediates the inhibitory effects of bone morphogenic proteins and G protein-coupled receptor 17 on oligodendroglia differentiation. ID2 expression is regulated by Wnt and histone deacetylases during the differentiation of OPC. ID4, another member of the ID family, functions similarly to ID2 in regulating the differentiation of OPC. The main difference is that ID4 is essential for oligodendrogenesis, whereas ID2 is nonessential. This could have important implications for demyelinating diseases, and interfering with these pathways might represent a viable therapeutic approach for these diseases.

Repression of Id2 expression by Gfi-1 is required for B-cell and myeloid development.

The development of mature blood cells from hematopoietic stem cells requires coordinated activities of transcriptional networks. Transcriptional repressor growth factor independence 1 (Gfi-1) is required for the development of B cells, T cells, neutrophils, and for the maintenance of hematopoietic stem cell function. However, the mechanisms by which Gfi-1 regulates hematopoiesis and how Gfi-1 integrates into transcriptional networks remain unclear. Here, we provide evidence that Id2 is a transcriptional target of Gfi-1, and repression of Id2 by Gfi-1 is required for B-cell and myeloid development. Gfi-1 binds to 3 conserved regions in the Id2 promoter and represses Id2 promoter activity in transient reporter assays. Increased Id2 expression was observed in multipotent progenitors, myeloid progenitors, T-cell progenitors, and B-cell progenitors in Gfi-1(-/-) mice. Knockdown of Id2 expression or heterozygosity at the Id2 locus partially rescues the B-cell and myeloid development but not the T-cell development in Gfi-1(-/-) mice. These studies demonstrate a role of Id2 in mediating Gfi-1 functions in B-cell and myeloid development and provide a direct link between Gfi-1 and the B-cell transcriptional network by its ability to repress Id2 expression.

Ebf1-mediated down-regulation of Id2 and Id3 is essential for specification of the B cell lineage.

Gene knockout experiments in mice have suggested a hierarchical model of early B cell commitment wherein E2A proteins (E47 and E12) activate early B cell factor (Ebf1), which in turn activates expression of the B cell commitment factor, Pax5. In IL-7 receptor alpha (IL-7Ralpha) knockout mice, B cell development is blocked before B-lineage commitment at the prepro-B cell stage in adult animals. In IL-7Ralpha(-/-) prepro-B cells, E47 is expressed and yet is insufficient to transcriptionally activate the putative downstream target gene, Ebf1. In this study, we show that further increases of E47 expression in IL-7Ralpha(-/-) prepro-B cells fails to activate Ebf1, but rather leads to a dramatic induction of the E2A inhibitory factors, Id2 and Id3. In contrast, enforced expression of Ebf1 in IL-7Ralpha(-/-) bone marrow potently down-regulates Id2 and Id3 mRNA expression and restores B cell differentiation in vivo. Down-regulation of both Id2 and Id3 during B cell specification is essential in that overexpression of either Id2 or Id3 in wild-type bone marrow blocks B cell specification at the prepro-B cell stage. Collectively, these studies suggest a model where Ebf1 induction specifies the B cell fate by dramatically increasing activity of E47 at the posttranslational level.

A duplicated copy of id2b is an unusual sex-determining candidate gene on the Y chromosome of arapaima (Arapaima gigas).

Arapaima gigas is one of the largest freshwater fish species of high ecological and economic importance. Overfishing and habitat destruction are severe threats to the remaining wild populations. By incorporating a chromosomal Hi-C contact map, we improved the arapaima genome assembly to chromosome-level, revealing an unexpected high degree of chromosome rearrangements during evolution of the bonytongues (Osteoglossiformes). Combining this new assembly with pool-sequencing of male and female genomes, we identified id2bbY, a duplicated copy of the inhibitor of DNA binding 2b (id2b) gene on the Y chromosome as candidate male sex-determining gene. A PCR-test for id2bbY was developed, demonstrating that this gene is a reliable male-specific marker for genotyping. Expression analyses showed that this gene is expressed in juvenile male gonads. Its paralog, id2ba, exhibits a male-biased expression in immature gonads. Transcriptome analyses and protein structure predictions confirm id2bbY as a prime candidate for the master sex-determiner. Acting through the TGFß signaling pathway, id2bbY from arapaima would provide the first evidence for a link of this family of transcriptional regulators to sex determination. Our study broadens our current understanding about the evolution of sex determination genetic networks and provide a tool for improving arapaima aquaculture for commercial and conservation purposes.

ID2 (inhibitor of DNA binding 2) is a rhythmically expressed transcriptional repressor required for circadian clock output in mouse liver.

Id2 is a helix-loop-helix transcription factor gene expressed in a circadian manner in multiple tissues with a phase-locked relationship with canonical clock genes. Our previous studies have identified circadian phenotypes in Id2 null mice, including enhanced photo-entrainment and disruption of activity rhythms, and have demonstrated a potent inhibitory effect of ID proteins upon CLOCK-BMAL1 transactivation of clock gene and clock-controlled gene activity. We have now begun to explore the potential role that ID2 may play in specifically regulating clock output. Here we show that ID2 protein is rhythmically expressed in mouse liver. Time-of-day-specific liver gene expression in Id2(+/+) and Id2(-/-) mice under circadian conditions was studied using DNA microarray analysis, identifying 651 differentially expressed genes, including a subset of 318 genes deemed rhythmically expressed in other studies. Examination of individual time courses reveals that these genes are dysregulated in a highly time-specific manner. A cohort of different functional groups were identified, including genes associated with glucose and lipid metabolism, e.g. serum protein Igfbp1 and lipoprotein lipase. We also reveal that the Id2(-/-) mice show a reduction in lipid storage in the liver and white adipose tissue, suggesting that disruption of normal circadian activity of components of lipid metabolism can result in overt physiological alterations. These data reveal a role for the transcriptional repressor ID2 as a circadian output regulator in the periphery.

(-)-Epigallocatechin-3-gallate induces Du145 prostate cancer cell death via downregulation of inhibitor of DNA binding 2, a dominant negative helix-loop-helix protein.

(-)-Epigallocatechin-3-gallate (EGCG) is one of the major polyphenol components in green tea. It effectively induces apoptosis in prostate cancer cells. The anticancer effect of this reagent is appealing because it is a natural component of a popular daily beverage that has proven harmless for thousands of years, making it a good candidate chemopreventive agent. EGCG suppresses cell growth and causes cell death, but the mechanisms are not well characterized, especially in androgen-independent prostate cancer cells. In the present study, using Affymetrix genechip Hu133 2.0, we analyzed the gene expression patterns of the androgen-independent prostate cancer cell line Du145, treated with or without EGCG, and found 40 genes whose expression levels were altered (>twofold, either upregulated or downregulated, P < 0.01) upon treatment with EGCG. These gene products are involved in the functions of transcription, RNA processing, protein folding, phosphorylation, protein degradation, cell motility, and ion transport. Among them, inhibitor of DNA binding 2 (ID2), known as a dominant anti-retinoblastoma (Rb) helix-loop-helix protein, was found to be downregulated fourfold by EGCG treatment. Forced expression of ID2 in Du145 cells reduced apoptosis and increased cell survival in the presence of EGCG, and knockdown ID2 expression in Du145 cells using a morpholino oligonucleotide specific for ID2 mimicked the apoptosis effect generated by EGCG treatment, although it was milder. To our knowledge, this is the first report indicating that ID2 is one of the critical factors in the signaling pathway of Du145 cell death induced by EGCG.