Cellular fate during development, differentiation, and function is tightly regulated and orchestrated in a hierarchical fashion by transcriptional activators and repressors. GATA-3 is one such master regulator of cellular fate, which was identified in 1990 along with two other GATA-family members and was found to be abundantly expressed in T lymphocytes and the brain (Yamamoto et al. 1990). GATA-3 was first described as a transcription factor that interacts with the TCR-α gene enhancer (Ho et al. 1991). It belongs to the GATA family of transcription factors that are conserved proteins containing one or two C2-C2 type zinc fingers and a highly conserved C4 zinc finger that recognizes a consensus DNA sequence A/TGATAA/G from which the name of the family originated (Merika and Orkin 1993; Labastie et al. 1994). The mammalian GATA family of transcription factors consists of six members: GATA-binding protein 1 (GATA-1)–GATA-6. These proteins are highly homologous, conserved among species, have distinctive tissue-specific expression patterns (Simon 1995), and play essential roles during vertebrate development (Kuo et al. 1997; Pandolfi et al. 1995; Tsai et al. 1994; Lowry and Atchley 2000). Based on their profile of tissue-specific expression, the GATA proteins can be classified as hematopoietic (GATA-1–GATA-3) or nonhematopoietic (GATA-4–GATA-6) (Merika and Orkin 1993; Simon 1995). In contrast to GATA-1 (Takahashi et al. 1998) and GATA-2 (Tsai et al. 1994) that are primarily expressed in hematopoietic cells, or GATA-4, -5, and -6 whose expression is restricted to mesoderm- and endoderm-derived tissues, such as the heart, liver, and intestines (Simon 1995; Kuo et al. 1997), GATA-3 is present in both hematopoietic (e.g., T cells) and nonhematopoietic tissues (George et al. 1994; Labastie et al. 1995; Debacker et al. 1999; Tong et al. 2000; Kaufman et al. 2003; Samson et al. 2003; Pai et al. 2004; Kouros-Mehr et al. 2006; Kim et al. 2006; Asselin-Labat et al. 2007; Ho and Pai 2007; Pai et al. 2008; Kouros-Mehr et al. 2008).
Similar to other GATA proteins, GATA-3 contains a distinct amino-terminal region that contains two transactivation domains followed by two highly conserved zinc-finger domains in which the C-terminal finger and the immediately adjacent conserved basic region together constitute the DNA-binding domain (Labastie et al. 1994; Lowry and Atchley 2000; Yang et al. 1994). The laboratory of Engel was the first to clone the GATA-3 gene and further dissected important biochemical properties of the GATA-3 protein (George et al. 1994). The entire coding region of the murine GATA-3 locus is approximately 23 kilo base pairs. The gene is composed of six exons. Exon 1 is untranslated and exon 2 contains the initiation codon for murine GATA-3. The amino and carboxy zinc fingers are encoded by exons 4 and 5, respectively. Exon 6 comprises the 3′ untranslated region and the polyadenylation signal (George et al. 1994). The murine GATA-3 cDNA clone encodes a protein of 443 amino acids with a molecular mass of 47,964 Da whose isoelectric point is around 9.89 (Ko et al. 1991). For GATA-3 to regulate gene expression, it must translocate from the cytoplasm into the nucleus to access its target genes. GATA-3 contains a classical nuclear import signal and is transported into the nucleus by importin-α (Yang et al. 1994). The affinity of GATA-3 to importin-α is regulated by phosphorylation, which is mediated by p38 mitogen-activated protein kinase (MAPK) (Maneechotesuwan et al. 2007). The GATA-3 protein is unstable with a short half-life (1 h) in developing Th2 cells (Yamashita et al. 2005). GATA-3 is ubiquitinated in vitro and in vivo and degraded by the 26 s proteasome pathway. The deletion of the ubiquitination sites lends stability to the protein (Yamashita et al. 2005).
GATA-3 is the main GATA family member that is expressed in immune cells and can be easily detected in developing and mature T cells, natural killer (NK) cells, and CD1-restricted natural killer T (NKT) cells (Ho et al. 1991; Samson et al. 2003; Oosterwegel et al. 1992). GATA-3 is not expressed in mast cells (Solymar et al. 2002). Beyond the immune system, GATA-3 is expressed in many embryonic and adult tissues, including the adrenal glands, kidneys, central nervous system, inner ear, hair follicles, skin, and breast tissue (mammary glands), and important functions for GATA-3 in several of these tissues have been shown in knockout and conditional knockout mouse models (Labastie et al. 1995; Tong et al. 2000; Kaufman et al. 2003; Kouros-Mehr et al. 2006; Asselin-Labat et al. 2007; Ho and Pai 2007; Kouros-Mehr et al. 2008; Chou et al. 2010). In immune cells, GATA-3 is best known to function as a master regulator of T helper 2 (Th2)-cell differentiation (Zhang et al. 1997; Zheng and Flavell 1997; Lee et al. 1998; Zhang et al. 1999). However, in recent years, GATA-3 has been found to have additional crucial functions in early T-cell commitment, β-selection, and CD4+ T cell development (Ho and Pai 2007; Ting et al. 1996; Hendriks et al. 1999; Chen and Zhang 2001; Hernandez-Hoyos et al. 2003; Pai et al. 2003; Tydell et al. 2007).
GATA-3 is a critical regulator in both mouse and human development. The expression pattern of GATA-3 during embryonic development, at least at the tissue level, is highly conserved among different vertebrates (Labastie et al. 1994; George et al. 1994; Debacker et al. 1999; Van Esch and Devriendt 2001). In human embryos, GATA-3 expression can be detected from the beginning of the 4th week of gestation (Debacker et al. 1999). From then on, GATA-3 transcripts are observed in various developing embryonic and fetal tissues, including the developing kidney (Labastie et al. 1994; Labastie et al. 1995), the parathyroids, and the inner ear (Debacker et al. 1999). GATA-3 null embryos die between E11 and E12 due to internal bleeding and display growth retardation, deformities in the brain and spinal cord, and gross aberrations in fetal liver hematopoiesis, suggesting that this gene is important in the development of various systems (Pandolfi et al. 1995). Haploinsufficiency of GATA-3 results in Barakat syndrome in humans, characterized by familial hypoparathyroidism, sensorineural deafness, and renal dysplasia (also known as HDR syndrome) and can be caused by mutations in GATA-3 that render it physically or functionally inactive (Van Esch and Devriendt 2001). Interestingly, mutations that abrogate the DNA-binding ability of GATA-3 are also found in human breast cancer specimens (Kouros-Mehr et al. 2006; Asselin-Labat et al. 2007; Kouros-Mehr et al. 2008; Chou et al. 2010).
GATA-3 Is Essential for T Cell Development
GATA-3 is one of the first genes that are transcriptionally activated in hematopoiesis as early as hematopoietic stem cells (HSCs) stage (Labastie et al. 1994; Debacker et al. 1999; Chen and Zhang 2001). GATA-3 mRNA is also expressed in the multipotent progenitors (MPPs) and at the pre-pro-B cell stage in the bone marrow. Its involvement during early stages of thymopoiesis was first proposed in 1996. Poorer Thy1+ cell development was shown in fetal thymus organ culture following introduction of antisense oligonucleotide to GATA-3 (Hattori et al. 1996). More definite information about the expression and role of GATA-3 in early stages of lymphopoiesis was provided by studies using various GATA-3 mutant mice. Collectively, these studies suggest that the major role of GATA-3 in thymopoiesis is to regulate the cellular differentiation of thymic stromal progenitors (TSPs) to ETPs and, in turn, downstream T cell development stages as well. Most likely the underlying mechanism does not involve cellular survival or proliferation although more conclusive investigations are required to support or dismiss the proposed hypothesis (Hosoya et al. 2010).
Overexpression strategies have been also used to explore the role of GATA-3 in thymopoiesis. Overexpression of GATA-3 resulted in induction of c-kit (Anderson et al. 2002; Taghon et al. 2007), which might be related to GATA-3-regulated ETP development in the thymus. In another study, retroviral overexpression of GATA-3 in mouse bone marrow Thy1.1lo LSK cells induced megakaryocyte and erythroid differentiation (Chen and Zhang 2001), as opposed to enhanced T cell development. Forced retroviral expression of GATA-3 in mouse fetal liver progenitors (Anderson et al. 2002) and committed lymphoid progenitors (Taghon et al. 2007) resulted in impaired development of T cells at various DN and DP stages. These studies collectively suggest that the expression level of GATA-3 decides the fate of lineage differentiation from early progenitors (Hosoya et al. 2010). It appears that a regulated low expression level of GATA-3 in prethymic progenitors is required to initiate thymopoiesis and induce T cell development.
Role of GATA-3 in the Development and Function of Other Hematopoietic Cells
In addition to T cells, GATA-3 is also expressed in other hematopoietic cell lineages such as natural killer (NK) cells (Samson et al. 2003) and CD1-restricted natural killer T (NKT) cells (Kim et al. 2006; Wang et al. 2006). Recent studies have proposed a potential role for GATA-3 in development, maturation, and function of invariant NKT cells (iNKT) (Kim et al. 2006). These cells are a unique subset of T cells expressing Vα14Jα18 (mouse) or Vα24Jα18 (human) T cell receptors, which often dimerize with Vβ8, Vβ7, or Vβ2. Similar to the conventional α/β T cells, iNKT cells also originate from thymic DP cells, but they are positively selected by CD1d molecules. Subsequent to successful positive selection, iNKT cells differentiate into either CD4+ or CD4-CD8- mature iNKT cells that constitute approximately 5% of the peripheral T cell pool (Kinjo and Kronenberg 2005). Following antigen encounter, this unique T cell subset has been shown to rapidly produce large amounts of various Th1 and Th2 cytokines including IFN-γ, IL-4, and IL-13, a phenomenon called cytokine storm (Wang et al. 2006; Kinjo and Kronenberg 2005). Over the years, multiple studies have demonstrated that iNKT cells play a crucial immunomodulatory role not only against infections but are also involved in autoimmunity, allergy, and cancer (Kinjo and Kronenberg 2005).
As in the case of α/β T cells, the role of GATA-3 in iNKT cell development, differentiation, and function was also studied by either loss-of-function approach or by enforced expression of GATA-3 in the system. Mice in which GATA-3 was deleted using Cd4-Cre were found to have near normal numbers of thymic iNKT cells, but interestingly the majority of these were CD4-CD8- with a selective loss of CD4 iNKT cells (Kim et al. 2006), which was similar to the loss of conventional CD4+ T cell in the absence of GATA-3 (Pai et al. 2003). Unlike in the thymus, there was a sixfold reduction of iNKT cells in peripheral lymphoid organs such as the spleen and almost complete lack in the liver suggestive of apoptosis of iNKT cells that did not develop or mature properly in the absence of GATA-3 indicated by failure to upregulate CD69 expression subsequent to their thymic egress (Kim et al. 2006). Lastly, GATA-3-deficient iNKT cells failed to respond to the NKT cell agonist α-galactosylceramide in vivo and mount a cytokine storm (Kim et al. 2006). This unresponsiveness is possibly due to defects in TCR signal transduction and was probably upstream of protein kinase C and calcium influx. This is because GATA-3-deficient iNKT cells were still capable of producing IFN-γ but not Th2 cytokines like IL-4, IL-5, or IL-13 which suggests that GATA-3 has a similar role in iNKT cells as in conventional T cells (Kim et al. 2006).
GATA-3 and Th2 Differentiation
The role of GATA-3 as a key transcription factor that is essential for Th2 differentiation is without doubt the most studied function of this protein. The role of this transcription factor as a master regulator of Th2 differentiation was independently codiscovered in the laboratories of Ray and Flavell (Zhang et al. 1997; Zheng and Flavell 1997). However, the initial clue for the involvement of GATA-3 in Th2 differentiation was provided by a prior study by Ray and colleagues that identified GATA-3 binding to the IL-5 promoter that was crucial for cyclic AMP-induced expression of the cytokine gene in T cells (Siegel et al. 1995). Subsequently, using Th1 or Th2 cells generated from naive CD4+ T cells and representational differential analysis (RDA), the role of GATA-3 in Th2 differentiation was established (Zhang et al. 1997; Zheng and Flavell 1997). Although GATA-3 was identified as a key factor for Th2 development, a careful analysis of regulation of the individual Th2 cytokine genes showed that unlike the IL-5 promoter, the IL-4 promoter, which lacked high affinity GATA-binding sites, was not directly regulated by GATA-3 (Zhang et al. 1998). Furthermore, in Th2 cells, antisense GATA-3 RNA inhibited IL-5 but not IL-4 promoter activation (Zhang et al. 1998). If GATA-3 was only responsible for IL-5 activation, how could it be a master Th2 regulator? Rao and colleagues showed that a distal enhancer in the IL-4 gene binds GATA-3 to induce its expression (Agarwal et al. 2000). In light of this study, it was not surprising when conditional deletion of GATA-3 from CD4 T cells resulted in global suppression of all Th2 cytokines that included IL-4, IL-5, and IL-13 (Zhu et al. 2004). Furthermore, deletion of GATA-3 resulted in Th1 differentiation without the requirement for IL-12 and IFN-γ, and inhibition of GATA-3 in differentiated Th2 cells caused a dramatic decrease in IL-5 and IL-13 expression although IL-4 expression was better preserved possibly due to the ability of other factors such as c-Maf that can directly regulate IL-4 but not IL-5 or IL-13 promoter activity (Zhu et al. 2004). These data taken together reiterated the dominant role of GATA-3 in Th2 differentiation. The expression of GATA-3 is significantly upregulated in human cells that express Th2 cytokine genes (Nakamura et al. 1999). Inhibiting its expression using siRNA strategy compromised Th2 differentiation, and similar data was obtained in individuals with the loss of one functional GATA-3 allele (Skapenko et al. 2004).
One of the important attributes of GATA-3 that makes it a dominant Th2 transcription factor is its ability to autoactivate itself. This property of GATA-3 was a serendipitous finding in the laboratory of Murphy when they were investigating the mechanism underlying the ability of GATA-3 to promote Th2 differentiation in a STAT6-independent fashion (Ouyang et al. 2000). These investigators found that activation of naïve CD4+T cells results in upregulation of endogenous GATA-3 expression, which was also evident in IL-4 /STAT6- deficient T cells indicating that this property was not dependent on the initial secretion of IL-4 (Ouyang et al. 2000). Thus the maintenance and amplification of the Th2 loop is efficiently promoted by autoactivation of endogenous GATA-3 expression. p38 MAPK was shown to be important for cAMP-mediated phosphorylation of GATA-3 that promotes Th2 cytokine gene expression (Chen et al. 2000). Interestingly, corticosteroids, which are commonly used to treat allergic diseases, have a potent inhibitory effect on GATA-3 in T cells by competing for importin-α and by inducing the expression of a p38 MAPK inhibitor (Maneechotesuwan et al. 2009).
GATA-3 in the Context of Other T Cell Transcription Factors
The induction and sustenance of a Th2 response is an intricately orchestrated process involving the concerted inhibition of select transcription factors while promoting others.
NF-κB Is Required for GATA-3 Expression in Differentiating Th2 Cells
Nuclear factor kappa B (NF-κB) is a transcription factor involved in TCR-induced activation signals in peripheral T cells. Mice lacking the p50 subunit of NF-κB showed impaired GATA-3 induction that blunted Th2 responses (Das et al. 2001). This defect was specific to Th2 cells since p50-deficient mice showed normal T-bet expression and secretion of the Th1 cytokine, IFN-γ. Importantly, this defect was restricted to the initial differentiation of Th2 cells, and inhibition of p50 activity in differentiated Th2 cells did not affect GATA-3 expression or secretion of Th2 cytokines (Das et al. 2001).
STAT5 and GATA-3 Synergize to Promote Th2 Phenotype
Naïve T cells require IL-2 for their differentiation and maintenance. IL-2 utilizes STAT5a and STAT5b for downstream signaling. Naïve T cells from STAT5a knockout mice are handicapped in their ability to differentiate into Th2 cells. In fact the constitutive expression of STAT5a in naïve T cells can induce the differentiation of Th2 cells even in the absence of IL-2 (Zhu et al. 2003). Furthermore, low TCR stimulation causes early IL-4 production, which is dependent on IL-2-mediated STAT5 signaling and also GATA-3. However, the early expression of GATA-3 can be achieved in an IL-4-independent fashion and is linked to autoactivation of GATA-3 expression (Ouyang et al. 2000). Also, neutralization of IL-2 cripples this early burst of IL-4 cytokine without compromising GATA-3 expression. Importantly, while the induction of a Th2 response has been shown to be dependent on both IL-2/STAT5 and GATA-3, these pathways operate independent of each other. GATA-3 is not considered to be downstream of IL-2 since the addition of IL-2 to in vitro culture can be delayed by 2 days without affecting the frequency of IL-4 producers (Zhu et al. 2003; Yamane et al. 2005). From these observations it became obvious that even if GATA-3 and STAT5 operate via independent pathways, these molecules synergize to promote Th2 responses. In fact, this hypothesis was proven correct in experiments in which forced expression of GATA-3 and STAT5 in naïve T cells or in Th1 cells induced a higher frequency of IL-4 producers when compared to cells expressing either factor alone (Zhu et al. 2006). While emphasizing the role of IL-2 in promoting Th2 responses it is also important to discuss the cooperation between GATA-3 and growth factor independent-1 (Gfi-1), which was initially cloned from an IL-2 independent cell line. The expression of this transcription factor is induced by IL-4 signaling in activated T cells and is dependent on STAT6. Deletion of Gfi-1 was shown to cause reduced expression of GATA-3 and IL-4. The few cells expressing GATA-3 in Gfi-1-deficient T cells were found to be unable to upregulate GATA-3 expression even with IL-2 supplementation. Conversely, forced expression of Gfi-1 in cells expressing high levels of GATA-3 resulted in a proliferative advantage of these cells. In summary, Gfi-1 is able to amplify the proliferation of high GATA-3-expressing CD4 T cells in response to IL-2 (Zhu et al. 2006). Taken together, these studies showed that Gfi-1, STAT5, and GATA-3 form the triad of Th2-promoting factors.
Notch and GATA-3
Notch signaling has been implicated in Th2 differentiation by directly regulating GATA-3 expression (Amsen et al. 2007) although more studies are needed to determine the importance of this regulation in vivo.
GATA-3 Dominates STAT6 in Th2 Induction
STAT6 is closely associated with Th2 responses and IL-13 and IL-4 trigger the phosphorylation of STAT6. Also, the kinetics of GATA-3 expression parallels STAT6 activation. Around the time that GATA-3 was established as a Th2 regulator, several studies also documented STAT6-independent pathway of Th2 cytokine production, further strengthening a dominant role for GATA-3 in Th2 differentiation (Dent et al. 1998; Sherman et al. 1999). The polarization of STAT6-deficient T cells under in vitro conditions does lead to the production of Th2 cytokines although less than that in WT cells, but more than in WT cells skewed under Th1 condition (Ouyang et al. 2000). Interestingly, analysis of DNaseI hypersensitivity sites in STAT6-deficient T cells reconstituted with GATA-3 reveals a pattern similar to that seen in WT cells, indicating that the chromatin remodeling fingerprint of a Th2 response is independent of STAT6 (Ouyang et al. 2000). Also, data from CTLA-4/STAT6 double knockout mice clearly show that in the absence of inhibitory signals, GATA-3 expression is sufficient to drive the differentiation of Th2 cells, illustrating the transcriptional dominance of GATA-3 in this process (Bour-Jordan et al. 2003). Although studies document evidence of STAT6-independent mechanisms of GATA-3 induction, the consensus is that STAT6 ensures optimal GATA-3 expression (Grogan et al. 2001).
GATA-3 Suppresses Th1 Induction by targeting STAT4 and STAT1
GATA-3 actively represses IL-12 and IFN-γ signaling both of which are critical for Th1 differentiation, implying a possible negative function of GATA-3 in Th1 development. Retroviral expression of GATA-3 during Th1 development results in the induction of Th2 phenotype with high levels of IL-4, IL-5, and IL-13 (Ferber et al. 1999). It was further revealed that the promotion of the Th2 phenotype could not simply be attributed to the high level of Th2 cytokines since the same results could be recapitulated in T cells deficient in both IL-4 and STAT6 and programmed towards a Th1 phenotype. GATA-3-mediated inhibition of Th1 differentiation is remarkable only when GATA-3 is introduced as early as day 1 in the Th1 differentiation program. If this “early development window” is missed then the effect of IL-12-mediated STAT4 signaling becomes dominant and expression of GATA-3 in committed Th1 cells results only in a modest decrease in IFN-γ and does not promote IL-4 production (Usui et al. 2003). Surprisingly, unlike in CD4 T cells, in NK cells, GATA-3 appears to be required for the production of IFN-γ (Samson et al. 2003). While there is no direct evidence that GATA-3 represses the promoter activity of IFN-γ, GATA-3 represses IL-12R β2 mRNA expression, thereby preventing IL-12 signaling during the early Th1 developmental window (Ouyang et al. 1998). Also GATA-3 expression significantly blunts STAT4 phosphorylation and promotes Th2 response. The mechanism behind GATA-3-mediated STAT4 suppression is unknown, but clearly the suppression of STAT4 phosphorylation is not mediated through effects on T-bet (Usui et al. 2003).
GATA-3 and NFAT1 Bind to an Enhancer Region in the IL-4 Gene
The NFAT family of transcription factors is activated by receptors involved in calcium mobilization, and their activation is blocked by cyclosporin A (CsA) and FK506. Rao and colleagues identified an enhancer region in the 3′ end of the IL-4 gene, designated VA, and showed that both NFAT and GATA-3 bind to this enhancer region suggesting an active cooperation between these transcription factors in enhancing the expression of IL-4 (Agarwal et al. 2000).
GATA-3 Derepresses RUNX3 Silencing of IL-4
RUNX (runt-related transcription factor) proteins dictate important T cell lineage choices and consist of three family members, RUNX1, 2, and 3. These proteins have unique DNA-binding subunits that complex with the non-DNA-binding subunit core-binding factor β. It has been recently shown that RUNX3 can bind to a silencer region in the IL-4 gene and repress expression of the IL-4 gene (Naoe et al. 2007; Djuretic et al. 2007). Interestingly, the expression of RUNX3 is similar in Th1 and Th2 cells, which suggests that another molecule is responsible for derepressing the suppressive effect mediated by RUNX3. In fact, forced overexpression of GATA-3 in Th1 cells results in the dissociation of RUNX3 from the IL-4 silencer region (Naoe et al. 2007). It is interesting to note how GATA-3 promotes IL-4 secretion without directly influencing its promoter activity.
Repressor of GATA (ROG)
Shortly following the discovery of GATA-3 in Th2 development, evidence for a GATA-3-interacting protein that repressed its activity was provided (Miaw et al. 2000). Repressor of GATA (ROG) was found to coimmunoprecipitate with GATA-3 and inhibited its ability to transactivate the IL-5 promoter (Hirahara et al. 2008). Overexpression of ROG completely inhibited the ability of GATA-3 to activate the IL-5 promoter. Also, ROG KO mice showed enhanced eosinophilia and airway responsiveness which was opposite of what was observed in mice expressing a GATA-3 dominant negative mutant (Hirahara et al. 2008).
T-Bet Represses GATA-3 Activity
T-bet, also called TBX21, is a member of the T-box gene family, and its role in Th1 commitment was discovered by the Glimcher laboratory shortly after the role of GATA-3 in Th2 development was identified (Szabo et al. 2000). With the discovery of T-bet and GATA-3 it seemed highly probable that cross-regulation between Th1 and Th2 cells might underlie some form of antagonism between these two master regulators. The first clue to T-bet-mediated suppression of GATA-3 came from T-bet knockout mice, which expressed high levels of endogenous GATA-3 (Finotto et al. 2002). Also, retroviral expression of T-bet in developed Th2 cells not only promoted IFN-γ production but also suppressed IL-4 and IL-5 production (Usui et al. 2006). This effect was found to be partly independent of STAT4. Furthermore, T-bet-deficient CD4 T cells produced IFN-γ if endogenous GATA-3 was suppressed that derepressed GATA-3-mediated inhibition of STAT4 (Finotto et al. 2002; Usui et al. 2006). The possibility of T-bet directly inhibiting GATA-3 was formally explored by Glimcher and colleagues (Hwang et al. 2005). It was shown that the phosphorylation of T-bet occurs as early as day 2 during Th1 skewing and is mediated by IL-2 inducible T cell kinase ITK, which results in the tyrosine phosphorylation of T-bet at position 525 (Hwang et al. 2005). Mutation of this tyrosine residue prevented the physical association between GATA-3 and T-bet. In fact, T-bet was shown to physically interact with the N-terminal region of GATA-3 once it was phosphorylated, and this sequestration of GATA-3 by T-bet prevented its binding to the IL-5 promoter. Thus an important function of T-bet is repression of GATA-3 binding to its target (Hwang et al. 2005).
A Role for GATA-3 in Innate Type 2 Immunity
In addition to Th2 cells, Type 2 innate lymphoid cells (ILC2s) also produce significant amounts of the type 2 cytokines IL-5 and IL-13 (Bernink et al. 2014; Martinez-Gonzalez et al. 2015). In these cells as well, type 2 cytokine production is regulated by GATA-3 (Hoyler et al. 2012; Tindemans et al. 2014). ILC2 cells in both mice and humans produce large amounts of IL-5 and IL-13 when activated by the epithelial cell-derived cytokines thymic stromal lymphopoietin (TSLP), IL-25, IL-33 (Lloyd and Saglani 2015), and prostaglandin D2 (PGD2) (Chang et al. 2014; Xue et al. 2014).
GATA-3 and Tregs
Regulatory T cells (Tregs) promote tolerance, and these cells express the transcription factor FOXP3, which is required for their suppressive activity. GATA-3 expression was described in Tregs (Wang et al. 2011; Wohlfert et al. 2011), and deletion of GATA-3 in FOXP3+ cells was shown to induce spontaneous autoimmunity (Wang et al. 2011). However, subsequent work failed to show any signs of autoimmunity in mice until 6 months of age (Rudra et al. 2012). In an elegant study using conditional gene knockout mice, it has been clearly shown that deletion of GATA-3 alone or of T-bet in FOXP3+ CD4+ T cells does not result in loss of Treg function but deletion of both induces spontaneous severe autoimmune-like disease due to upregulation of RORγt and generation of Th17 cells (Yu et al. 2015). Thus, increase in GATA-3 or T-bet expression in Foxp3+ T cells appears to be transient and most likely related to suppression of RORγt by cross-regulation to maintain immune homeostasis.
In contrast to situations in the steady-state, where GATA-3 expression may serve to limit Th17 development, increase in GATA-3 expression in Tregs during inflammation causes loss of Treg function as previously reported by us (Krishnamoorthy et al. 2012). In this study, infection of newborn mice by respiratory syncytial virus (RSV), RSV being the most common respiratory pathogen in early life, upregulated GATA-3 and IL-13 expression in FOXP3+ CD4+ T cells and caused total loss of Treg function with promotion of airway inflammation and mucus production (Krishnamoorthy et al. 2012). This effect of RSV in neonates may be an important contributor to the association of RSV-induced severe bronchiolitis in newborns with increased risk for asthma in later life as noted in many epidemiological studies (Sigurs et al. 2000; Wu et al. 2008).
GATA-3 and Disease
GATA-3 and Asthma
Asthma is a pathological condition associated with an overzealous Th2 response in response to innocuous antigens resulting in mucus production and eosinophilic infiltration. Studies have documented that asthmatics have a higher percentage of CD4+ T cells producing IL-4, IL-5, and IL-13, which are secreted in the airways of patients with asthma (Walker et al. 1992; Robinson et al. 1992; Ray and Cohn 1999). The association of elevated Th2 responses and asthma underscores an important role for GATA-3 in the disease process. In fact, GATA-3 mRNA expression is significantly increased in the airways of asthmatic subjects compared with that in normal control subjects and positively correlates with IL-5 expression (Nakamura et al. 1999). Mice expressing a dominant negative mutant of GATA-3 demonstrate reduced inflammation, low IgE levels, and blunted eosinophilia (Zhang et al. 1999). Similarly, delivering antisense GATA-3 reduced airway inflammation (Finotto et al. 2001). The dominant effect of GATA-3 in driving an asthmatic response is further evident from studies analyzing the repressive effects mediated by other transcription molecules on GATA-3. For example, mice deficient in ROG display enhanced airway hyperresponsiveness and inflammation in response to Th2-specific antigenic stimulation (Hirahara et al. 2008). T-bet-deficient mice demonstrate spontaneous induction of asthma even in the absence of immunological challenge with enhanced eosinophilia and airway hyperresponsiveness (Finotto et al. 2002).
In a recent clinical trial in humans, mild allergic asthmatics subjected to allergen provocation were treated with a GATA-3-specific DNAzyme to blunt GATA-3 expression. This approach led to significant attenuation of both early and late asthmatic responses in the treated subjects (Homburg et al. 2015; Krug et al. 2015). However, more studies are needed in the absence of allergen challenge to determine whether inhibition of GATA-3 activity can control clinical features of mild asthma. Given that type 2 cytokines remain elevated in the airways of some severe asthmatics even in the context of high-dose corticosteroid (CS) therapy (Raundhal et al. 2015), it is possible that targeting GATA-3 will achieve some degree of disease control in this group of asthmatics who respond poorly to CS, the standard therapy for asthma.
GATA-3 and Breast Cancer
In recent years, a dominant role for GATA-3 in development of mammary cells has come to light. Deletion of GATA-3 driven by K14-Cre resulted in the failure to develop mammary placcodes. GATA-3 has been shown to have a dominant function in controlling the development of luminal cells in the mammary gland and the maintenance of the differentiated phenotype of the luminal cells in the adult mammary gland (Kouros-Mehr et al. 2006; Asselin-Labat et al. 2007). More recently, bioinformatic analysis of breast cancer specimens revealed loss of expression of GATA-3 in poorly differentiated and highly metastatic tumors (Kouros-Mehr et al. 2008).
This work was supported by National Institutes of Health grants AI048927, AI106684 and HL113956 (to A.R.), and AI100012 and HL122307 (to P.R.).