MRG1, the product of a melanocyte-specific gene related gene, is a cytokine-inducible transcription factor with transformation activity

Cited2 is a key regulator of placental development and plasticity

The biology of trophoblast cell lineage development and placentation is characterized by the involvement of several known transcription factors. Central to the action of a subset of these transcriptional regulators is CBP-p300 interacting transactivator with Glu/Asp-rich carboxy-terminal domain 2 (CITED2). CITED2 acts as a coregulator modulating transcription factor activities and affecting placental development and adaptations to physiological stressors. These actions of CITED2 on the trophoblast cell lineage and placentation are conserved across the mouse, rat, and human. Thus, aspects of CITED2 biology in hemochorial placentation can be effectively modeled in the mouse and rat. In this review, we present information on the conserved role of CITED2 in the biology of placentation and discuss the use of CITED2 as a tool to discover new insights into regulatory mechanisms controlling placental development.

Exploring the role of CITED transcriptional regulators in the control of macrophage polarization

Macrophages are tissue resident innate phagocytic cells that take on contrasting phenotypes, or polarization states, in response to the changing combination of microbial and cytokine signals at sites of infection. During the opening stages of an infection, macrophages adopt the proinflammatory, highly antimicrobial M1 state, later shifting to an anti-inflammatory, pro-tissue repair M2 state as the infection resolves. The changes in gene expression underlying these transitions are primarily governed by nuclear factor kappaB (NF-κB), Janus kinase (JAK)/signal transducer and activation of transcription (STAT), and hypoxia-inducible factor 1 (HIF1) transcription factors, the activity of which must be carefully controlled to ensure an effective yet spatially and temporally restricted inflammatory response. While much of this control is provided by pathway-specific feedback loops, recent work has shown that the transcriptional co-regulators of the CBP/p300-interacting transactivator with glutamic acid/aspartic acid-rich carboxy-terminal domain (CITED) family serve as common controllers for these pathways. In this review, we describe how CITED proteins regulate polarization-associated gene expression changes by controlling the ability of transcription factors to form chromatin complexes with the histone acetyltransferase, CBP/p300. We will also cover how differences in the interactions between CITED1 and 2 with CBP/p300 drive their contrasting effects on pro-inflammatory gene expression.

Dysregulation of CITED2 in abnormal lung development in the nitrofen rat model

PURPOSE

CITED2 both modulates lung, heart and diaphragm development. The role of CITED2 in the pathogenesis of congenital diaphragmatic hernia (CDH) is unknown. We aimed to study CITED2 during abnormal lung development in the nitrofen model.

METHODS

Timed-pregnant rats were given nitrofen on embryonic day (E) 9 to induce CDH. Fetal lungs were harvested on E15, 18 and 21. We performed RT-qPCR, RNAscope™ in situ hybridization and immunofluorescence staining for CITED2.

RESULTS

We observed no difference in RT-qPCR (control: 1.09 ± 0.22 and nitrofen: 0.95 ± 0.18, p = 0.64) and in situ hybridization (1.03 ± 0.03; 1.04 ± 0.03, p = 0.97) for CITED2 expression in E15 nitrofen and control pups. At E18, CITED2 expression was reduced in in situ hybridization of nitrofen lungs (1.47 ± 0.05; 1.14 ± 0.07, p = 0.0006), but not altered in RT-qPCR (1.04 ± 0.16; 0.81 ± 0.13, p = 0.33). In E21 nitrofen lungs, CITED2 RNA expression was increased in RT-qPCR (1.04 ± 0.11; 1.52 ± 0.17, p = 0.03) and in situ hybridization (1.08 ± 0.07, 1.29 ± 0.04, p = 0.02). CITED2 protein abundance was higher in immunofluorescence staining of E21 nitrofen lungs (2.96 × 109 ± 0.13 × 109; 4.82 × 109 ± 0.25 × 109, p < 0.0001).

CONCLUSION

Our data suggest that dysregulation of CITED2 contributes to abnormal lung development of CDH, as demonstrated by the distinct spatial-temporal distribution in nitrofen-induced lungs.

Myeloid-CITED2 Deficiency Exacerbates Diet-Induced Obesity and Pro-Inflammatory Macrophage Response

Macrophages are the principal component of the innate immune system that are found in all tissues and play an essential role in development, homeostasis, tissue repair, and immunity. Clinical and experimental studies have shown that transcriptionally dynamic pro-inflammatory macrophages are involved in the pathogenesis of diet-induced obesity and insulin resistance. However, cell-intrinsic mechanisms must exist that bridle uncontrolled pro-inflammatory macrophage activation in metabolic organs and disease pathogenesis. In this study, we show that CBP/p300-interacting transactivator with glutamic acid/aspartic acid-rich carboxyl-terminal domain 2 (CITED2) is an essential negative regulator of pro-inflammatory macrophage activation and inflammatory disease pathogenesis. Our in vivo studies show that myeloid-CITED2 deficiency significantly elevates high-fat diet (HFD)-induced expansion of adipose tissue volume, obesity, glucose intolerance, and insulin resistance. Moreover, myeloid-CITED2 deficiency also substantially augments HFD-induced adipose tissue inflammation and adverse remodeling of adipocytes. Our integrated transcriptomics and gene set enrichment analyses show that CITED2 deficiency curtails BCL6 signaling and broadly elevates BCL6-repressive gene target expression in macrophages. Using complementary gain- and loss-of-function studies, we found that CITED2 deficiency attenuates, and CITED2 overexpression elevates, inducible BCL6 expression in macrophages. At the molecular level, our analyses show that CITED2 promotes BCL6 expression by restraining STAT5 activation in macrophages. Interestingly, siRNA-mediated knockdown of STAT5 fully reversed elevated pro-inflammatory gene target expression in CITED2-deficient macrophages. Overall, our findings highlight that CITED2 restrains inflammation by promoting BCL6 expression in macrophages, and limits diet-induced obesity and insulin resistance.

Role of FBXL5 in redox homeostasis and spindle assembly during oocyte maturation in mice

As an E3 ubiquitin ligase, F-box and leucine-rich repeat protein 5 (FBXL5) participates in diverse biologic processes. However, the role of Fbxl5 in mouse oocyte meiotic maturation has not yet been fully elucidated. The present study revealed that mouse oocytes depleted of Fbxl5 were unable to complete meiosis, as Fbxl5 silencing led to oocyte meiotic failure with reduced rates of GVBD and polar body extrusion. In addition, Fbxl5 depletion induced aberrant mitochondrial dynamics as we noted the overproduction of reactive oxygen species (ROS) and the accumulation of phosphorylated γH2AX with Fbxl5 knockdown. We also found that Fbxl5-KD led to the abnormal accumulation of CITED2 proteins in mouse oocytes. Our in vitro ubiquitination assay showed that FBXL5 interacted with CITED2 and that it mediated the degradation of CITED2 protein through the ubiquitination-proteasome pathway. Collectively, our data revealed critical functions of FBXL5 in redox hemostasis and spindle assembly during mouse oocyte maturation.

CITED2 inhibits STAT1-IRF1 signaling and atherogenesis

Macrophages are the principal component of the innate immune system. They play very crucial and multifaceted roles in the pathogenesis of inflammatory vascular diseases. There is an increasing recognition that transcriptionally dynamic macrophages are the key players in the pathogenesis of inflammatory vascular diseases. In this context, the accumulation and aberrant activation of macrophages in the subendothelial layers govern atherosclerotic plaque development. Macrophage-mediated inflammation is an explicitly robust biological response that involves broad alterations in inflammatory gene expression. Thus, cell-intrinsic negative regulatory mechanisms must exist which can restrain inflammatory response in a spatiotemporal manner. In this study, we identified CBP/p300-interacting transactivator with glutamic acid/aspartic acid-rich carboxyl-terminal domain 2 (CITED2) as one such cell-intrinsic negative regulator of inflammation. Our in vivo studies show that myeloid-CITED2-deficient mice on the Apoe^-/- background have larger atherosclerotic lesions on both control and high-fat/high-cholesterol diets. Our integrated transcriptomics and gene set enrichment analyses studies show that CITED2 deficiency elevates STAT1 and interferon regulatory factor 1 (IRF1) regulated pro-inflammatory gene expression in macrophages. At the molecular level, our studies identify that CITED2 deficiency elevates IFNγ-induced STAT1 transcriptional activity and STAT1 enrichment on IRF1 promoter in macrophages. More importantly, siRNA-mediated knockdown of IRF1 completely reversed elevated pro-inflammatory target gene expression in CITED2-deficient macrophages. Collectively, our study findings demonstrate that CITED2 restrains the STAT1-IRF1 signaling axis in macrophages and limits the development of atherosclerotic plaques.

Downregulation of SUV39H1 and CITED2 Exerts Additive Effect on Promoting Adipogenic Commitment of Human Mesenchymal Stem Cells

Human adipogenesis is the process through which uncommitted human mesenchymal stem cells (hMSCs) differentiate into adipocytes. Through a siRNA-based high-throughput screen that identifies adipogenic regulators whose expression knockdown leads to enhanced adipogenic differentiation of hMSCs, two new regulators, SUV39H1, a histone methyltransferase that catalyzes H3K9Me3, and CITED2, a CBP/p300-interacting transactivator with Glu/Asp-rich carboxy-terminal domain 2 were uncovered. Both SUV39H1 and CITED2 are normally downregulated during adipogenic differentiation of hMSCs. Further expression knockdown induced by siSUV39H1 or siCITED2 at the adipogenic initiation stage significantly enhanced adipogenic differentiation of hMSCs as compared with siControl treatment, with siSUV39H1 acting by both accelerating fat accumulation in individual adipocytes and increasing the total number of committed adipocytes, whereas siCITED2 acting predominantly by increasing the total number of committed adipocytes. In addition, both siSUV39H1 and siCITED2 were able to redirect hMSCs to undergo adipogenic differentiation in the presence of osteogenic inducing media, which normally only induces osteogenic differentiation of hMSCs in the absence of siSUV39H1 or siCITED2. Interestingly, simultaneous knockdown of both SUV39H1 and CITED2 resulted in even greater levels of adipogenic differentiation of hMSCs and expression of CEBPα and PPARγ, two master regulators of adipogenesis, as compared with those elicited by single gene knockdown. Furthermore, the effects of co-knockdown were equivalent to the additive effect of individual gene knockdown. Taken together, this study demonstrates that SUV39H1 and CITED2 are both negative regulators of human adipogenesis, and downregulation of both genes exerts an additive effect on promoting adipogenic differentiation of hMSCs through augmented commitment.

Role of CITED2 in stem cells and cancer

Cbp/P300 interacting transactivator with Glu/Asp-rich carboxy-terminal domain 2 (CITED2) is a transcription co-factor that interacts with several other transcription factors and co-factors, and serves critical roles in fundamental cell processes, including proliferation, apoptosis, differentiation, migration and autophagy. The interacting transcription factors or co-factors of CITED2 include LIM homeobox 2, transcription factor AP-2, SMAD2/3, peroxisome proliferator-activated receptor γ, oestrogen receptor, MYC, Nucleolin and p300/CBP, which regulate downstream gene expression, and serve important roles in the aforementioned fundamental cell processes. Emerging evidence has demonstrated that CITED2 serves an essential role in embryonic and adult tissue stem cells, including hematopoietic stem cells and tendon-derived stem/progenitor cells. Additionally, CITED2 has been reported to function in different types of cancer. Although the functions of CITED2 in different tissues vary depending on the interaction partner, altered CITED2 expression or altered interactions with transcription factors or co-factors result in alterations of fundamental cell processes, and may affect stem cell maintenance or cancer cell survival. The aim of this review is to summarize the molecular mechanisms of CITED2 function and how it serves a role in stem cells and different types of cancer based on the currently available literature.

CITED2 and the modulation of the hypoxic response in cancer

CITED2 (CBP/p300-interacting transactivator with Glu/Asp-rich C-terminal domain, 2) is a ubiquitously expressed protein exhibiting a high affinity for the CH1 domain of the transcriptional co-activators CBP/p300, for which it competes with hypoxia-inducible factors (HIFs). CITED2 is particularly efficient in the inhibition of HIF-1α-dependent transcription in different contexts, ranging from organ development and metabolic homeostasis to tissue regeneration and immunity, being also potentially involved in various other physiological processes. In addition, CITED2 plays an important role in inhibiting HIF in some diseases, including kidney and heart diseases and type 2-diabetes. In the particular case of cancer, CITED2 either functions by promoting or suppressing cancer development depending on the context and type of tumors. For instance, CITED2 overexpression promotes breast and prostate cancers, as well as acute myeloid leukemia, while its expression is downregulated to sustain colorectal cancer and hepatocellular carcinoma. In addition, the role of CITED2 in the maintenance of cancer stem cells reveals its potential as a target in non-small cell lung carcinoma and acute myeloid leukemia, for example. But besides the wide body of evidence linking both CITED2 and HIF signaling to carcinogenesis, little data is available regarding CITED2 role as a negative regulator of HIF-1α specifically in cancer. Therefore, comprehensive studies exploring further the interactions of these two important mediators in cancer-specific models are sorely needed and this can potentially lead to the development of novel targeted therapies.

Identification of duplicated Cited3 genes and their responses to hypoxic stress in blunt snout bream (Megalobrama amblycephala)

The CITED3 protein is a non-DNA-binding transcriptional co-regulator involved in the regulation of various transcriptional responses against hypoxia stress. Here, we characterized two paralogs Cited3 genes (Cited3a and Cited3b) from blunt snout bream (Megalobrama amblycephala), which is a hypoxia-sensitive species. Both genes have an open reading frame of 756 and 723 bp; encoded a protein of 251 amino acid and 240 amino acid, respectively; and they shared a sequence identity of 67%. In adult fish, both Cited3a and Cited3b mRNAs were highly expressed in kidney tissues. In contrast, they were detected in the skin, muscle, and gonad at extraordinarily low levels. During embryogenesis, both Cited3a and Cited3b mRNAs were maternally deposited in eggs and fluctuated from the zygote to the 44-hpf (hours post-fertilization) larvae. Whole-mount in situ hybridization demonstrated that both Cited3a and Cited3b mRNAs were transcribed in the brain, gut, and tailbud at 12 hpf, and at the brain and gut at 24 hpf, and at the brain at 36 hpf embryos. Hypoxic treatment led to upregulated expression of the Cited3 genes during embryogenesis. Under hypoxia, both Cited3a and Cited3b genes in the kidney and brain and Cited3a genes in the liver were significantly upregulated. These results suggest that hypoxia was associated with increases in mRNA levels for both Cited3a (kidney, brain, liver) and Cited3b (kidney and liver).

An estrogen receptor (ER)-related signature in predicting prognosis of ER-positive breast cancer following endocrine treatment

Quite a few estrogen receptor (ER)‐positive breast cancer patients receiving endocrine therapy are at risk of disease recurrence and death. ER‐related genes are involved in the progression and chemoresistance of breast cancer. In this study, we identified an ER‐related gene signature that can predict the prognosis of ER‐positive breast cancer patient receiving endocrine therapy. We collected RNA expression profiling from Gene Expression Omnibus database. An ER‐related signature was developed to separate patients into high‐risk and low‐risk groups. Patients in the low‐risk group had significantly better survival than those in the high‐risk group. ROC analysis indicated that this signature exhibited good diagnostic efficiency for the 1‐, 3‐ and 5‐year disease‐relapse events. Moreover, multivariate Cox regression analysis demonstrated that the ER‐related signature was an independent risk factor when adjusting for several clinical signatures. The prognostic value of this signature was validated in the validation sets. In addition, a nomogram was built and the calibration plots analysis indicated the good performance of this nomogram. In conclusion, combining with ER status, our results demonstrated that the ER‐related prognostic signature is a promising method for predicting the prognosis of ER‐positive breast cancer patients receiving endocrine therapy.

Transcriptional regulators CITED2 and PU.1 cooperate in maintaining hematopoietic stem cells

Reduced expression of the transcription factor PU.1 is frequently associated with development of acute myeloid leukemia (AML), whereas elevated levels of CITED2 (CBP/p300-interacting-transactivator-with-an-ED-rich-tail 2) enhance maintenance of both normal and leukemic hematopoietic stem and progenitor cells (HSPCs). Recent findings indicate that PU.1 and CITED2 act in the same gene regulatory network. We therefore examined a potential synergistic effect of simultaneous PU.1 downregulation and CITED2 upregulation on stem cell biology and AML pathogenesis. We found that simultaneous PU.1/CITED2 deregulation in human CD34⁺ cord blood (CB) cells, as well as CITED2 upregulation in preleukemic murine PU.1-knockdown (PU.1^KD/KD) bone marrow cells, significantly increased the maintenance of HSPCs compared with the respective deregulation of either factor alone. Increased replating capacity of PU.1^KD/KD/CITED2 cells in in vitro assays eventually resulted in outgrowth of transformed cells, while upregulation of CITED2 in PU.1^KD/KD cells enhanced their engraftment in in vivo transplantation studies without affecting leukemic transformation. Transcriptional analysis of CD34⁺ CB cells with combined PU.1/CITED2 alterations revealed a set of differentially expressed genes that highly correlated with gene signatures found in various AML subtypes. These findings illustrate that combined PU.1/CITED2 deregulation induces a transcriptional program that promotes HSPC maintenance, which might be a prerequisite for malignant transformation.

CITED2 mediates the cross-talk between mechanical loading and IL-4 to promote chondroprotection

Osteoarthritis (OA) pathogenesis is mediated largely through the actions of proteolytic enzymes such as matrix metalloproteinase (MMP) 13. The transcriptional regulator CITED2, which suppresses the expression of MMP13 in chondrocytes, is induced by interleukin (IL)-4 in T cells and macrophages, and by moderate mechanical loading in chondrocytes. We tested the hypothesis that CITED2 mediates cross-talk between IL-4 signaling and mechanical loading-induced pathways that result in chondroprotection, at least in part, by downregulating MMP13. IL-4 induced CITED2 gene expression in human chondrocytes in a dose- and time-dependent manner through JAK/STAT signaling. Mechanical loading combined with IL-4 resulted in additive effects on inducing CITED2 expression and downregulating of MMP13 in human chondrocytes in vitro. In vivo, IL-4 gene knockout (KO) mice exhibited reduced basal levels of CITED2 expression in chondrocytes. While moderate treadmill running induced CITED2 expression and reduced MMP13 expression in wild-type mice, these effects were blunted (for CITED2) or abolished (for MMP13) in chondrocytes of IL-4 gene KO mice. Moreover, intra-articular injections of mouse recombinant IL-4 combined with regular cage activity mitigated post-traumatic OA to a greater degree compared to immobilized mice treated with IL-4 alone. These data suggest that using moderate loading to enhance IL-4 may be a potential therapeutic strategy for chondroprotection in OA.

Aberrant expression of CITED2 promotes prostate cancer metastasis by activating the nucleolin-AKT pathway

Despite many efforts to develop hormone therapy and chemotherapy, no effective strategy to suppress prostate cancer metastasis has been established because the metastasis is not well understood. We here investigate a role of CBP/p300-interacting transactivator with E/D-rich carboxy-terminal domain-2 (CITED2) in prostate cancer metastasis. CITED2 is highly expressed in metastatic prostate cancer, and its expression is correlated with poor survival. The CITED2 gene is highly activated by ETS-related gene that is overexpressed due to chromosomal translocation. CITED2 acts as a molecular chaperone to guide PRMT5 and p300 to nucleolin, thereby activating nucleolin. Informatics and experimental data suggest that the CITED2-nucleolin axis is involved in prostate cancer metastasis. This axis stimulates cell migration through the epithelial-mesenchymal transition and promotes cancer metastasis in a xenograft mouse model. Our results suggest that CITED2 plays a metastasis-promoting role in prostate cancer and thus could be a target for preventing prostate cancer metastasis.

Down-regulation of CITED2 attenuates breast tumor growth, vessel formation and TGF-β-induced expression of VEGFA

While we previously demonstrated that CITED2 expression in primary breast tumor tissues is elevated relative to normal mammary epithelium and inversely correlated with patient survival, its functional impact on primary tumor development and progression remained unknown. To address this issue, we examined the effect of CITED2 silencing on the growth of human breast cancer cell lines MDA-MB-231 and MDA-MB-468 following orthotopic administration in vivo. Here, we show that CITED2 silencing significantly attenuated MDA-MB-231 primary tumor growth concordant with reduced tumor vascularization, while MDA-MB-468 primary tumor growth and tumor vascularization remained unaffected. Correspondingly, expression of VEGFA was significantly reduced in shCITED2-expressing MDA-MB-231, but not MDA-MB-468 tumors. Consistent with the observed pattern of vascularization and VEGFA expression, we found that TGF-β stimulation induced expression of VEGFA and enhanced CITED2 recruitment to the VEGFA promoter in MDA-MA-231 cells, while failing to induce VEGFA expression in MDA-MB-468 cells. Further supporting its involvement in TGF-β-induced expression of VEGFA, CITED2 silencing prevented TGF-β induction of VEGFA expression in MDA-MB-231 cells. Collectively, these data indicate that CITED2 regulates primary breast tumor growth, likely by influencing tumor vasculature via TGF-β-dependent regulation of VEGFA.

CITED2 attenuates macrophage recruitment concordant with the downregulation of CCL20 in breast cancer cells

The transcriptional co-regulator Cbp/p300-interacting transactivator with Glu/Asp-rich carboxy-terminal domain-2 (CITED2) may promote breast tumor growth; however, the mechanisms by which its effects are mediated remain to be fully elucidated. Tumor-associated macrophages serve an important function in tumor development and progression and are recruited by chemotactic factors produced by cells within the tumor microenvironment. The present study assessed the effects of CITED2 silencing on macrophage recruitment in two xenograft mouse models of human breast cancer, one in which tumor growth was sensitive to CITED2 silencing (MDA-MB-231) and one in which it was insensitive (MDA-MB-468). The present study identified that silencing CITED2 significantly attenuated macrophage infiltration in MDA-MB-231 but not MDA-MB-468 orthotopic tumors, concordant with its effect on tumor growth. Correspondingly, conditioned media obtained from CITED2-silenced MDA-MB-231 cells exhibited a significantly decreased ability to induce macrophage recruitment by Transwell migration assay, whereas the chemotactic effect of MDA-MB-468 conditioned media was unaffected. Examining the expression of macrophage chemoattractants within orthotopic tumors and tumor cell-conditioned media revealed a significant decrease in C-C motif chemokine ligand (CCL)20 mRNA and protein expression following CITED2-silencing in MDA-MB-231 cells, compared with that in cells transfected with scramble shRNA. However, mRNA and protein expression was unaffected by CITED2-silencing in MDA-MB-468 cells. Furthermore, chromatin immunoprecipitation analysis revealed that CITED2 was localized to the CCL20 promoter in MDA-MB-231 cells, suggesting that it serves a direct function in its regulation, which is consistent with the effect of CITED2 silencing on CCL20 expression. Lastly, neutralizing CCL20 in the conditioned media of MDA-MB-231 cells significantly inhibited macrophage recruitment. Collectively, these results suggest that CITED2 is involved in modulating macrophage recruitment, representing a novel mechanism through which it may influence tumor growth. This may be partly mediated by regulating tumor cell production of the chemokine CCL20.

CITED2 in breast carcinoma as a potent prognostic predictor associated with proliferation, migration and chemoresistance

CITED2 (Cbp/p300‐interacting transactivator, with Glu/Asp‐rich carboxy‐terminal domain, 2) is a member of the CITED family and is involved in various cellular functions during development and differentiation. Mounting evidence suggests the importance of CITED in the progression of human malignancies, but the significance of CITED2 protein has not yet been examined in breast carcinoma. Therefore, in the present study, we examined the clinical significance and the biological functions of CITED2 in breast carcinoma by immunohistochemistry and in vitro study. CITED2 immunoreactivity was detected in breast carcinoma tissues, and it was significantly higher compared to those in morphologically normal mammary glands. CITED2 immunoreactivity was significantly associated with stage, pathological T factor, lymph node metastasis, histological grade, HER2 and Ki‐67, and inversely correlated with estrogen receptor. Moreover, the immunohistochemical CITED2 status was significantly associated with increased incidence of recurrence and breast cancer‐specific death of the breast cancer patients, and multivariate analyses demonstrated CITED2 status as an independent worse prognostic factor for disease‐free and breast cancer‐specific survival. Subsequent in vitro experiments showed that CITED2 expression significantly increased proliferation activity and migration property in MCF‐7and S KBR‐3 breast carcinoma cells. Moreover, CITED2 caused chemoresistance to epirubicin and 5‐fluorouracil, but not paclitaxel, in these cells, and it inhibited p53 accumulation after 5‐fluorouracil treatment in MCF‐7 cells. These results suggest that CITED2 plays important roles in the progression and chemoresistance of breast carcinoma and that CITED2 status is a potent prognostic factor in breast cancer patients.

CITED2 Modulates Breast Cancer Metastatic Ability through Effects on IKKα

Previously, we identified the transcriptional coactivator CITED2 as a potential facilitator of bone metastasis using a murine mammary cancer model. Extending these studies to human breast cancer, it was observed that CITED2 mRNA expression was significantly elevated in patient specimens of metastatic breast cancer relative to primary tumors, with highest levels in metastasis to bone relative to non-bone sites. To further evaluate CITED2 functions in breast cancer metastasis, CITED2 expression was stably reduced in the human breast cancer cell lines MDA-MB-231 and MDA-MB-468, which are metastatic in animal models. While CITED2 knockdown had no effect on cell proliferation, cell migration and invasion were significantly reduced, as was the establishment of metastasis following intracardiac administration in athymic nude mice. To explore the mechanism behind these effects, gene expression following CITED2 knockdown in MDA-MB-231 cells by cDNA microarray was performed. As confirmed at the mRNA and protein levels in both MDA-MB-231 and MDA-MB-468 cells, expression of the NF-κB regulator IKKα was significantly reduced, along with several NF-κB targets with known roles in metastasis (OPN, MMP9, uPA, SPARC, IL11, and IL1β). Furthermore, ChIP assay revealed recruitment of CITED2 to the promoter of IKKα, indicating a direct role in regulating its expression. Consistent with reduced IKKα expression, CITED2 knockdown inhibited both canonical and noncanonical NF-κB signaling. Finally, restoration of IKKα expression following CITED2 knockdown in MDA-MB-231 and MDA-MB-468 cells rescued their invasive ability. Collectively, these data demonstrate that CITED2 modulates metastatic ability in human breast cancer cells, at least in part, through the regulation of IKKα.

IMPLICATIONS

The current study highlights the role of CITED2 in facilitating breast cancer metastasis, partly via regulation of IKKα. Mol Cancer Res; 14(8); 730-9. ©2016 AACR.

CITED2 silencing sensitizes cancer cells to cisplatin by inhibiting p53 trans-activation and chromatin relaxation on the ERCC1 DNA repair gene

In this study, we show that silencing of CITED2 using small-hairpin RNA (shCITED2) induced DNA damage and reduction of ERCC1 gene expression in HEK293, HeLa and H1299 cells, even in the absence of cisplatin. In contrast, ectopic expression of ERCC1 significantly reduced intrinsic and induced DNA damage levels, and rescued the effects of CITED2 silencing on cell viability. The effects of CITED2 silencing on DNA repair and cell death were associated with p53 activity. Furthermore, CITED2 silencing caused severe elimination of the p300 protein and markers of relaxed chromatin (acetylated H3 and H4, i.e. H3K9Ac and H3K14Ac) in HEK293 cells. Chromatin immunoprecipitation assays further revealed that DNA damage induced binding of p53 along with H3K9Ac or H3K14Ac at the ERCC1 promoter, an effect which was almost entirely abrogated by silencing of CITED2 or p300. Moreover, lentivirus-based CITED2 silencing sensitized HeLa cell line-derived tumor xenografts to cisplatin in immune-deficient mice. These results demonstrate that CITED2/p300 can be recruited by p53 at the promoter of the repair gene ERCC1 in response to cisplatin-induced DNA damage. The CITED2/p300/p53/ERCC1 pathway is thus involved in the cell response to cisplatin and represents a potential target for cancer therapy.

MicroRNAs in the Myocyte Enhancer Factor 2 (MEF2)-regulated Gtl2-Dio3 Noncoding RNA Locus Promote Cardiomyocyte Proliferation by Targeting the Transcriptional Coactivator Cited2

Understanding cell cycle regulation in postmitotic cardiomyocytes may lead to new therapeutic approaches to regenerate damaged cardiac tissue. We have demonstrated previously that microRNAs encoded by the Gtl2-Dio3 noncoding RNA locus function downstream of the MEF2A transcription factor in skeletal muscle regeneration. We have also reported expression of these miRNAs in the heart. Here we investigated the role of two Gtl2-Dio3 miRNAs, miR-410 and miR-495, in cardiac muscle. Overexpression of miR-410 and miR-495 robustly stimulated cardiomyocyte DNA synthesis and proliferation. Interestingly, unlike our findings in skeletal muscle, these miRNAs did not modulate the activity of the WNT signaling pathway. Instead, these miRNAs targeted Cited2, a coactivator required for proper cardiac development. Consistent with miR-410 and miR-495 overexpression, siRNA knockdown of Cited2 in neonatal cardiomyocytes resulted in robust proliferation. This phenotype was associated with reduced expression of Cdkn1c/p57/Kip2, a cell cycle inhibitor, and increased expression of VEGFA, a growth factor with proliferation-promoting effects. Therefore, miR-410 and miR-495 are among a growing number of miRNAs that have the ability to potently stimulate neonatal cardiomyocyte proliferation.

Cited2 is required for the maintenance of glycolytic metabolism in adult hematopoietic stem cells

Mammalian adult hematopoietic stem cells (HSCs) reside in the hypoxic bone marrow microenvironment and display a distinct metabolic phenotype compared with their progenitors. It has been proposed that HSCs generate energy mainly through anaerobic glycolysis in a pyruvate dehydrogenase kinase (Pdk)-dependent manner. Cited2 is an essential regulator for HSC quiescence, apoptosis, and function. Herein, we show that conditional deletion of Cited2 in murine HSCs results in elevated levels of reactive oxygen species, decreased cellular glutathione content, increased mitochondrial activity, and decreased glycolysis. At the molecular level, Cited2 deficiency significantly reduced the expression of genes involved in metabolism, such as Pdk2, Pdk4, and lactate dehydrogenases B and D (LDHB and LDHD). Cited2-deficient HSCs also exhibited increased Akt signaling, concomitant with elevated mTORC1 activity and phosphorylation of FoxOs. Further, inhibition of PI3/Akt, but not mTORC1, partially rescued the repression of Pdk4 caused by deletion of Cited2. Altogether, our results suggest that Cited2 is required for the maintenance of adult HSC glycolytic metabolism likely through regulating Pdk2, Pdk4, LDHB, LDHD, and Akt activity.

Cited2 in hematopoietic stem cell function

PURPOSE OF REVIEW

Transcription co-regulator Cited2 is essential for mouse development. Recent work has shown that Cited2 plays important roles in normal hematopoiesis in fetal liver and adult bone marrow. This review focuses on the function of Cited2 in the maintenance of hematopoietic stem cells (HSCs) and its potential role in the metabolic regulation of HSCs.

RECENT FINDINGS

Fetal liver cells from Cited2 null embryos give rise to reduced numbers of hematopoietic colonies and display significantly impaired hematopoietic reconstitution capacity. In adult mice, conditional deletion of Cited2 markedly reduces the number of HSCs and compromises hematopoietic reconstitution in mice receiving a transplant of Cited2 deficient bone marrow cells. Additional deletion of Ink4a/Arf or p53 in a Cited2-deficient background restores HSC functionality. Meanwhile, Cited2 deficient HSCs display loss of quiescence, which can be partially rescued by additional deletion of hypoxia inducible factor-1α.

SUMMARY

Cited2 is an essential regulator in fetal liver and adult hematopoiesis. Further studies into the function of Cited2 and the underlying mechanism in the metabolic regulation of HSCs will provide a better understanding of the connection between energy metabolism and HSC quiescence and self-renewal. Investigations of the pathologic role of Cited2 in leukemogenesis may yield useful information in developing effective therapeutic strategies.

CITED2 modulates estrogen receptor transcriptional activity in breast cancer cells

Cbp/p300-interacting transactivator with Glu/Asp-rich carboxy-terminal domain 2 (CITED2) is a member of the CITED family of non-DNA binding transcriptional co-activators of the p300/CBP-mediated transcription complex. Previously, we identified CITED2 as being overexpressed in human breast tumors relative to normal mammary epithelium. Upon further investigation within the estrogen receptor (ER)-positive subset of these breast tumor samples, we found that CITED2 mRNA expression was elevated in those associated with poor survival. In light of this observation, we investigated the effect of elevated CITED2 levels on ER function. While ectopic overexpression of CITED2 in three ER-positive breast cancer cell lines (MCF-7, T47D, and CAMA-1) did not alter cell proliferation in complete media, growth was markedly enhanced in the absence of exogenous estrogen. Correspondingly, cells overexpressing CITED2 demonstrated reduced sensitivity to the growth inhibitory effects of the selective estrogen receptor modulator, 4-hydroxytamoxifen. Subsequent studies revealed that basal ER transcriptional activity was elevated in CITED2-overexpressing cells and was further increased upon the addition of estrogen. Similarly, basal and estrogen-induced expression of the ER-regulated genes trefoil factor 1 (TFF1) and progesterone receptor (PGR) was higher in cells overexpressing CITED2. Concordant with this observation, ChIP analysis revealed higher basal levels of CITED2 localized to the TFF-1 and PGR promoters in cells with ectopic overexpression of CITED2, and these levels were elevated further in response to estrogen stimulation. Taken together, these data indicate that CITED2 functions as a transcriptional co-activator of ER in breast cancer cells and that its increased expression in tumors may result in estrogen-independent ER activation, thereby reducing estrogen dependence and response to anti-estrogen therapy.

Indoxyl sulfate signals for rapid mRNA stabilization of Cbp/p300-interacting transactivator with Glu/Asp-rich carboxy-terminal domain 2 (CITED2) and suppresses the expression of hypoxia-inducible genes in experimental CKD and uremia

Chronic hypoxia in the tubulointerstitium serves as a final common pathway in progressive renal disease. Circumstantial evidence suggests that hypoxia-inducible factor (HIF)-1 in the ischemic tubules may be functionally inhibited in a chronic kidney disease (CKD) milieu. In this study, we hypothesized that indoxyl sulfate (IS), a uremic toxin, impairs the cellular hypoxic response. In human kidney (HK-2) proximal tubular cells, IS reduced the hypoxic induction of HIF-1 target genes. This effect was not associated with quantitative changes in the HIF-1α protein, but with functional impairment of the HIF-1α C-terminal transactivation domain (CTAD). Among factors that impeded the recruitment of transcriptional coactivators to the HIF-1αCTAD, IS markedly up-regulated Cbp/p300-interacting transactivator with Glu/Asp-rich carboxy-terminal domain 2 (CITED2) through a mechanism of post-transcriptional mRNA stabilization involving the extracellular signal-regulated kinase (ERK) 1/2 pathway. In vivo, disproportionate expression of HIF target genes was demonstrated in several CKD models, which was offset by an oral adsorbent, AST-120. Furthermore, administration of indole reduced the induction of angiogenic, hypoxia-inducible genes in rats with experimental heart failure. Results of these studies reveal a novel role of IS in modulating the transcriptional response of HIF-1 and provide insight into molecular mechanisms underlying progressive nephropathies as well as cardiovascular complications.

Functional significance of SRJ domain mutations in CITED2

CITED2 is a transcriptional co-activator with 3 conserved domains shared with other CITED family members and a unique Serine-Glycine Rich Junction (SRJ) that is highly conserved in placental mammals. Loss of Cited2 in mice results in cardiac and aortic arch malformations, adrenal agenesis, neural tube and placental defects, and partially penetrant defects in left-right patterning. By screening 1126 sporadic congenital heart disease (CHD) cases and 1227 controls, we identified 19 variants, including 5 unique non-synonymous sequence variations (N62S, R92G, T166N, G180-A187del and A187T) in patients. Many of the CHD-specific variants identified in this and previous studies cluster in the SRJ domain. Transient transfection experiments show that T166N mutation impairs TFAP2 co-activation function and ES cell proliferation. We find that CITED2 is phosphorylated by MAPK1 in vitro at T166, and that MAPK1 activation enhances the coactivation function of CITED2 but not of CITED2-T166N. In order to investigate the functional significance in vivo, we generated a T166N mutation of mouse Cited2. We also used PhiC31 integrase-mediated cassette exchange to generate a Cited2 knock-in allele replacing the mouse Cited2 coding sequence with human CITED2 and with a mutant form deleting the entire SRJ domain. Mouse embryos expressing only CITED2-T166N or CITED2-SRJ-deleted alleles surprisingly show no morphological abnormalities, and mice are viable and fertile. These results indicate that the SRJ domain is dispensable for these functions of CITED2 in mice and that mutations clustering in the SRJ region are unlikely to be the sole cause of the malformations observed in patients with sporadic CHD. Our results also suggest that coding sequence mutations observed in case-control studies need validation using in vivo models and that predictions based on structural conservation and in vitro functional assays, or even in vivo global loss of function models, may be insufficient.

CITED2 functions as a molecular switch of cytokine-induced proliferation and quiescence

Transforming growth factor-α (TGF-α)-induced proliferation and transforming growth factor-β (TGF-β)-mediated quiescence are intricately balanced in normal lung-tissue homeostasis but are deregulated during neoplastic progression of lung cancer. Here, we show that Cbp/p300-interacting transactivator with Glu/Asp-rich carboxy-terminal domain 2 (CITED2), a novel MYC-interacting transcriptional modulator, responds to TGF-α induction and TGF-β suppression to orchestrate cellular proliferation and quiescence, respectively. Upon TGF-α induction, CITED2 was induced by MYC and further modulated MYC-mediated transcription in a feed-forward manner. CITED2 recruited p300 to promote MYC-p300-mediated transactivation of E2F3, leading to increased G1/S cell cycle progression. Moreover, CITED2 inhibited cellular quiescence by enhancing MYC-mediated suppression of p21(CIP1). CITED2 interacted with histone deacetylase 1 (HDAC1) and potentiated MYC-HDAC1 complex formation. TGF-β stimulation provoked downregulation of CITED2, which abrogated MYC-HDAC1-mediated p21(CIP1) suppression, causing cellular quiescence. Ectopic CITED2 expression enhanced tumor growth in nude mice; furthermore, CITED2 knockdown caused tumor shrinkage and increased overall host mouse survival rates. Expression of CITED2/MYC/E2F3/p21(CIP1) signaling molecules was associated with poor prognosis of lung cancer patients. Thus, CITED2 functions as a molecular switch of TGF-α and TGF-β-induced growth control, and MYC-CITED2 signaling axis provides a new index for predicting clinical outcome.

HIF-1α deletion partially rescues defects of hematopoietic stem cell quiescence caused by Cited2 deficiency

Cited2 is a transcriptional modulator involved in various biologic processes including fetal liver hematopoiesis. In the present study, the function of Cited2 in adult hematopoiesis was investigated in conditional knockout mice. Deletion of Cited2 using Mx1-Cre resulted in increased hematopoietic stem cell (HSC) apoptosis, loss of quiescence, and increased cycling, leading to a severely impaired reconstitution capacity as assessed by 5-fluorouracil treatment and long-term transplantation. Transcriptional profiling revealed that multiple HSC quiescence- and hypoxia-related genes such as Egr1, p57, and Hes1 were affected in Cited2-deficient HSCs. Because Cited2 is a negative regulator of HIF-1, which is essential for maintaining HSC quiescence, and because we demonstrated previously that decreased HIF-1α gene dosage partially rescues both cardiac and lens defects caused by Cited2 deficiency, we generated Cited2 and HIF-1α double-knockout mice. Additional deletion of HIF-1α in Cited2-knockout BM partially rescued impaired HSC quiescence and reconstitution capacity. At the transcriptional level, deletion of HIF-1α restored expression of p57 and Hes1 but not Egr1 to normal levels. Our results suggest that Cited2 regulates HSC quiescence through both HIF-1-dependent and HIF-1-independent pathways.

Pre-B cell leukemia homeobox 1 is associated with lupus susceptibility in mice and humans

Sle1a.1 is part of the Sle1 susceptibility locus, which has the strongest association with lupus nephritis in the NZM2410 mouse model. In this study, we show that Sle1a.1 results in the production of activated and autoreactive CD4(+) T cells. Additionally, Sle1a.1 expression reduces the peripheral regulatory T cell pool, as well as induces a defective response of CD4(+) T cells to the retinoic acid expansion of TGF-β-induced regulatory T cells. At the molecular level, Sle1a.1 corresponds to an increased expression of a novel splice isoform of Pbx1, Pbx1-d. Pbx1-d overexpression is sufficient to induce an activated/inflammatory phenotype in Jurkat T cells and to decrease their apoptotic response to retinoic acid. PBX1-d is expressed more frequently in the CD4(+) T cells from lupus patients than from healthy controls, and its presence correlates with an increased central memory T cell population. These findings indicate that Pbx1 is a novel lupus susceptibility gene that regulates T cell activation and tolerance.

Mechanotransduction and cartilage integrity

Osteoarthritis (OA) is characterized by the breakdown of articular cartilage that is mediated in part by increased production of matrix metalloproteinases (MMPs) and aggrecanases (ADAMTS), enzymes that degrade components of the cartilage extracellular matrix. Efforts to design synthetic inhibitors of MMPs/ADAMTS have only led to limited clinical success. In addition to pharmacologic therapies, physiologic joint loading is widely recommended as a nonpharmacologic approach to improve joint function in osteoarthritis. Clinical trials report that moderate levels of exercise exert beneficial effects, such as improvements in pain and physical function. Experimental studies demonstrate that mechanical loading mitigates joint destruction through the downregulation of MMPs/ADAMTS. However, the molecular mechanisms underlying these effects of physiologic loading on arthritic joints are not well understood. We review here the recent progress on mechanotransduction in articular joints, highlighting the mediators and pathways in the maintenance of cartilage integrity, especially in the prevention of cartilage degradation in OA.

Knockdown of CITED2 using short-hairpin RNA sensitizes cancer cells to cisplatin through stabilization of p53 and enhancement of p53-dependent apoptosis

CITED2 is a transcriptional modulator which has been implicated in human oncogenesis. In the present study, we examined whether CITED2 is also involved in the resistance of cancer cells to the chemotherapeutic drug cisplatin. We first observed that knockdown of CITED2 using short-hairpin RNA sensitized non-tumorigenic HEK293 cells to cisplatin. Sensitization to cisplatin following knockdown of CITED2 was also observed in cervical carcinoma HeLa cells and in cisplatin-resistant HeLa cells, thereby showing that acquired cisplatin resistance could be reversed by CITED2 knockdown. This sensitization response was dependent on the status of p53 since efficient sensitization was observed in p53-positive hepatocellular carcinoma (HCC) Sk-Hep-1 cells, whereas a negligible response was produced in the two p53-defective cell lines HCC Mahlavu and lung cancer H1299. In contrast, overexpression of CITED2 decreased sensitivity of HEK293 cells to cisplatin, while moderate resistance was produced in HeLa cells. Overexpression of CITED2 also decreased sensitivity to cisplatin in p53-defective H1299 cells when exogenous p53 expression was re-introduced. We observed that knockdown of CITED2-induced CBP/p300-mediated p53 acetylation (Lys373) in HEK293 cells, thereby leading to a decrease of p53 ubiquitination and subsequent accumulation of the p53 protein. Notably, the effects of CITED2 knockdown on p53 accumulation and the increase of p53's target Bax were more pronounced after treatment with cisplatin. Based on these results, we propose that a combination of cisplatin and CITED2 shRNA may represent an effective treatment against p53-sensitive cancer cells.

Mechanical intervention for maintenance of cartilage and bone

Mechanical loading provides indispensible stimuli for growth and development of the articular cartilage and bone. Interestingly, depending on loading conditions loads applied to the joint can be beneficial as well as harmful to skeletal maintenance and remodeling. Moderate loads to the synovial joint, for instance, suppress the expression levels of matrix metallproteinases (MMPs), while loads above a threshold tend to increase their destructive activities. This report focuses on two recently developed loading modalities from animal studies, joint motion and joint loading. Their unique characteristics and potential usages for maintenance of the articular cartilage and stimulation of bone remodeling are reviewed. Also described are biophysical and molecular mechanisms which likely are responsible for the load-driven maintenance of cartilage and bone, and a possibility of developing load-mediated treatments of osteoporosis and osteoarthritis.

Tendon-derived stem/progenitor cell aging: defective self-renewal and altered fate

Aging is a major risk factor for tendon injury and impaired tendon healing, but the basis for these relationships remains poorly understood. Here we show that rat tendon- derived stem ⁄ progenitor cells (TSPCs) differ in both self-renewal and differentiation capability with age. The frequency of TSPCs in tendon tissues of aged animals is markedly reduced based on colony formation assays. Proliferation rate is decreased, cell cycle progression is delayed and cell fate patterns are also altered in aged TSPCs. In particular, expression of tendon lineage marker genes is reduced while adipocytic differentiation increased. Cited2, a multi-stimuli responsive transactivator involved in cell growth and senescence, is also downregulated in aged TSPCs while CD44, a matrix assembling and organizing protein implicated in tendon healing, is upregulated, suggesting that these genes participate in the control of TSPC function.

Cited2 is an essential regulator of adult hematopoietic stem cells

The regulatory pathways necessary for the maintenance of adult hematopoietic stem cells (HSCs) remain poorly defined. By using loss-of-function approaches, we report a selective and cell-autonomous requirement for the p300/CBP-binding transcriptional coactivator Cited2 in adult HSC maintenance. Conditional deletion of Cited2 in the adult mouse results in loss of HSCs causing multilineage bone marrow failure and increased lethality. In contrast, conditional ablation of Cited2 after lineage specification in lymphoid and myeloid lineages has no impact on the maintenance of these lineages. Additional deletion of Ink4a/Arf (encoding p16(Ink4a) and p19(Arf)) or Trp53 (encoding p53, a downstream target of p19(Arf)) in a Cited2-deficient background restores HSC functionality and rescues mice from bone marrow failure. Furthermore, we show that the critical role of Cited2 in primitive hematopoietic cells is conserved in humans. Taken together, our studies provide genetic evidence that Cited2 selectively maintains adult HSC functions, at least in part, via Ink4a/Arf and Trp53.

Functional characterization of two CITED3 homologs (gcCITED3a and gcCITED3b) in the hypoxia-tolerant grass carp, Ctenopharyngodon idellus

Background

CITED proteins belong to a family of non-DNA-binding transcriptional co-regulators that are characterized by a conserved ED-rich domain at the C-terminus. This family of genes is involved in the regulation of a variety of transcriptional responses through interactions with the CBP/p300 integrators and various transcription factors. In fish, very little is known about the expression and functions of CITEDs.

Results

We have characterized two closely related but distinct CITED3 genes, gcCited3a and gcCited3b, from the hypoxia-tolerant grass carp. The deduced gcCITED3a and gcCITED3b proteins share 72% amino acid identity, and are highly similar to the CITED3 proteins of both chicken and Xenopus. Northern blot analysis indicates that the mRNA expression of gcCited3a and gcCited3b is strongly induced by hypoxia in the kidney and liver, respectively. Luciferase reporter assays demonstrated that both gene promoters are activated by gcHIF-1. Further, ChIP assays comparing normal and hypoxic conditions reveal differential in vivo binding of gcHIF-1 to both gene promoters in kidney and liver tissues. HRE-luciferase reporter assays demonstrated that both gcCITED3a and gcCITED3b proteins inhibit gcHIF-1 transcriptional activity, and GST pull-down assays confirmed that both proteins bind specifically to the CH1 domain of the grass carp p300 protein.

Conclusion

The grass carp gcCITED3a and gcCITED3b genes are differentially expressed and regulated in different fish organs in response to hypoxic stress. This is the first report demonstrating in vivo regulation of two closely-related CITED3 isogenes by HIF-1, as well as CITED3 regulation of HIF-1 transcriptional activity in fish. Overall, our findings suggest that unique molecular mechanisms operate through these two gcCITED3 isoforms that likely play an important regulatory role in the hypoxic response in the grass carp.

Conditional deletion of Cited2 results in defective corneal epithelial morphogenesis and maintenance

Cited2 is an important transcriptional cofactor involved in multiple organ development. Gene profile analysis has identified Cited2 as one of the transcription factors expressed at high levels in adult mouse cornea. To address the function of Cited2 in corneal morphogenesis, we deleted Cited2 in surface ectoderm derived ocular structures including cornea by crossing Cited2-floxed mice with Le-Cre transgenic mice. Cited2(flox/flox);Le-Cre(+) eyes invariably displayed corneal opacity and developed spontaneous corneal neovascularization at older age. Fewer layers of corneal epithelial cells and the absence of cytokeratin 12 (K12) expression featured Cited2 deficient postnatal and adult eyes. Cited2 deficient cornea exhibited impaired healing in response to corneal epithelial debridement by manifesting abnormal histology, lack of K12 expression and corneal neovascularization. Moreover, mechanistic studies suggest that Cited2 may play a role in corneal morphogenesis in part through modulating the expression of Pax6 and Klf4. Collectively, these findings demonstrate a novel function of Cited2 in postnatal corneal morphogenesis and maintenance. Our study will help better understand the molecular mechanisms involved in corneal biology, and more importantly, it may provide a valuable animal model for testing therapeutics in the treatment of corneal disorders, especially blindness as a result of corneal epithelial cell deficiency.

Identification of CITED2 as a negative regulator of fracture healing

The transcription regulator CITED2 (CBP/p300-Interacting-Transactivator-with-ED-rich-tail-2) is known to suppress genes mediating angiogenesis and extracellular matrix (ECM) remodeling. However, it is unclear whether CITED2 has a role in controlling skeletal repair or remodeling. We tested the hypothesis that CITED2 functions in bone fracture healing by suppressing the expression of genes critical to ECM remodeling, angiogenesis and osteogenesis, importantly the matrix metalloproteinases (MMPs). Three hours following mandibular osteotomy or sham surgery of adult rats, osteotomy fronts were harvested and the expression of CITED2 and genes associated with fracture healing was ascertained by quantitative PCR. In parallel, gain-of-function studies examined the effect of overexpressing CITED2 on the expression and activity of several MMPs. In the fractured mandible, CITED2 expression was inversely related to the expression of MMP-2, -3, -9, -13, VEGF, HIF-1alpha, M-CSF, RANK-L, and OPG. Consistent with this, the over-expression of CITED2 in osteoblasts inhibited the expression and activity of MMP-2, -3, -9, and -13. Taken together, the studies suggest that CITED2 is a critical upstream regulator of fracture healing. The suppression of CITED2 early after fracture may allow an optimal initiation of the healing response.

Cited2 is required for the proper formation of the hyaloid vasculature and for lens morphogenesis

Cited2 is a transcriptional modulator with pivotal roles in different biological processes. Cited2-deficient mouse embryos manifested two major defects in the developing eye. An abnormal corneal-lenticular stalk was characteristic of Cited2(-/-) developing eyes, a feature reminiscent of Peters' anomaly, which can be rescued by increased Pax6 gene dosage in Cited2(-/-) embryonic eyes. In addition, the hyaloid vascular system showed hyaloid hypercellularity consisting of aberrant vasculature, which might be correlated with increased VEGF expression in the lens. Deletion of Hif1a (which encodes HIF-1alpha) in Cited2(-/-) lens specifically eliminated the excessive accumulation of cellular mass and aberrant vasculature in the developing vitreous without affecting the corneal-lenticular stalk phenotype. These in vivo data demonstrate for the first time dual functions for Cited2: one upstream of, or together with, Pax6 in lens morphogenesis; and another in the normal formation of the hyaloid vasculature through its negative modulation of HIF-1 signaling. Taken together, our study provides novel mechanistic revelation for lens morphogenesis and hyaloid vasculature formation and hence might offer new insights into the etiology of Peters' anomaly and ocular hypervascularity.

CITED2 signals through peroxisome proliferator-activated receptor-gamma to regulate death of cortical neurons after DNA damage

DNA damage is an important initiator of neuronal apoptosis and activates signaling events not yet fully defined. Using the camptothecin-induced DNA damage model in neurons, we previously showed that cyclin D1-associated cell cycle cyclin-dependent kinases (Cdks) (Cdk4/6) and p53 activation are two major events leading to activation of the mitochondrial apoptotic pathway. With gene array analyses, we detected upregulation of Cited2, a CBP (cAMP response element-binding protein-binding protein)/p300 interacting transactivator, in response to DNA damage. This upregulation was confirmed by reverse transcription-PCR and Western blot. CITED2 was functionally important because CITED2 overexpression promotes death, whereas CITED2 deficiency protects. Cited2 upregulation is upstream of the mitochondrial death pathway (BAX, Apaf1, or cytochrome c release) and appears to be independent of p53. However, inhibition of the Cdk4 blocked Cited2 induction. The Cited2 prodeath mechanism does not involve Bmi-1 or p53. Instead, Cited2 activates peroxisome proliferator-activated receptor-gamma (PPARgamma), an activity that we demonstrate is critical for DNA damage-induced death. These results define a novel neuronal prodeath pathway in which Cdk4-mediated regulation of Cited2 activates PPARgamma and consequently caspase.

The protein arginine methyltransferases CARM1 and PRMT1 cooperate in gene regulation

Protein arginine methyltransferases (PRMT) have been implicated in the regulation of transcription. They are recruited to promoters via interaction with transcription factors and exert their coactivator function by methylating arginine residues in histones and other chromatin proteins. Here, we employ an unbiased approach to identify novel target genes, which are under the control of two members of the enzyme family, PRMT1 and CARM1/PRMT4 (coactivator associated arginine methyltransferase 1). By using cDNA microarray analysis, we find that the siRNA-mediated single knockdown of neither CARM1 nor PRMT1 causes significant changes in gene expression. In contrast, double knockdown of both enzymes results in the deregulated expression of a large group of genes, among them the CITED2 gene. Cytokine-stimulated expression analysis indicates that transcriptional activation of CITED2 depends on STAT5 and the coactivation of both PRMTs. ChIP analysis identifies the CITED2 gene as a direct target gene of STAT5, CARM1 and PRMT1. In reporter gene assays, we show that STAT5-mediated transcription is cooperatively enhanced by CARM1 and PRMT1. Interaction assays reveal a cytokine-induced association of STAT5 and the two PRMTs. Our data demonstrate a widespread cooperation of CARM1 and PRMT1 in gene activation as well as repression and that STAT5-dependent transcription of the CITED2 gene is a novel pathway coactivated by the two methyltransferases.

Global profiling of influence of intra-ischemic brain temperature on gene expression in rat brain

Mild to moderate differences in brain temperature are known to greatly affect the outcome of cerebral ischemia. The impact of brain temperature on ischemic disorders has been mainly evaluated through pathological analysis. However, no comprehensive analyses have been conducted at the gene expression level. Using a high-density oligonucleotide microarray, we screened 24000 genes in the hippocampus under hypothermic (32 degrees C), normothermic (37 degrees C), and hyperthermic (39 degrees C) conditions in a rat ischemia-reperfusion model. When the ischemic group at each intra-ischemic brain temperature was compared to a sham-operated control group, genes whose expression levels changed more than three-fold with statistical significance could be detected. In our screening condition, thirty-three genes (some of them novel) were obtained after screening, and extensive functional surveys and literature reviews were subsequently performed. In the hypothermic condition, many neuroprotective factor genes were obtained, whereas cell death- and cell damage-associated genes were detected as the brain temperature increased. At all intra-ischemic brain temperatures, multiple molecular chaperone genes were obtained. The finding that intra-ischemic brain temperature affects the expression level of many genes related to neuroprotection or neurotoxicity coincides with the different pathological outcomes at different brain temperatures, demonstrating the utility of the genetic approach.

The specific contribution of hypoxia-inducible factor-2alpha to hypoxic gene expression in vitro is limited and modulated by cell type-specific and exogenous factors

Cellular integrity in hypoxia is dependent on molecular adaptations dominated by the heterodimeric transcription factor hypoxia-inducible factor (HIF). The HIF complex contains one of two alternative oxygen-regulated alpha-subunits considered to play distinct roles in the hypoxia response. Although HIF-2alpha may be more important in tumour biology and erythropoiesis, the spectrum of individual target genes is still insufficiently characterized. We therefore performed an Affymetrix gene array on Hep3B cells stimulated with a hypoxia-mimetic and transfected with either HIF-1alpha or HIF-2alpha siRNA. 271 transcripts were found to be induced HIF-dependently, including most previously identified HIF targets and a number of novel genes. Most were influenced by HIF-1alpha knock-down, whereas a smaller number were regulated by HIF-2alpha. Validation of a selection of genes by RNase protection confirmed the hypoxic regulation and HIF-1alpha- or HIF-2alpha-dependency in most cases, with the latter showing a lower amplitude. Many HIF-2alpha targets also responded to HIF-1alpha knock-down. Interestingly, regulation by HIF-2alpha was markedly influenced not only by cell type, but also by cell culture conditions, features that were not shared with HIF-1alpha-regulated genes. Thus, HIF-2alpha effects are modulated by a number of intrinsic and extrinsic factors which may be most relevant in tumour cells.

Cited2 is required for fetal lung maturation

Lung maturation at the terminal sac stage of lung development is characterized by a coordinated increase in terminal sac formation and vascular development in conjunction with the differentiation of alveolar type I and type II epithelial cells. The Cited2-Tcfap2a/c complex has been shown to activate transcription of Erbb3 and Pitx2c during mouse development. In this study, we show that E17.5 to E18.5 Cited2-null lungs had significantly reduced terminal sac space due to an altered differentiation of type I and type II alveolar epithelial cells. In addition, E17 Cited2-null lungs exhibited a decrease in the number of apoptotic cells, contributing to the loss in airspace. Consistent with the phenotype, genes associated with alveolar cell differentiation and survival were differentially expressed in Cited2-null fetal lungs compared to those of wild-type littermates. Moreover, expression of Cebpa, a key regulator of airway epithelial maturation, was significantly decreased in Cited2-null fetal lungs. Cited2 and Tcfap2c were present on the Cebpa promoter in E18.5 lungs to activate Cebpa transcription. We propose that the Cited2-Tcfap2c complex controls lung maturation by regulating Cebpa expression. Understanding the function of this complex may provide novel therapeutic strategies for patients with respiratory distress syndromes.

A role for CITED2, a CBP/p300 interacting protein, in colon cancer cell invasion

A thorough understanding of histone acetyltransferase CBP/p300-mediated regulation of gene expression and cell growth is essential to identify mechanisms relevant to the development of histone deacetylase (HDAC) inhibitor-based preventive and therapeutic strategies. We found that knockdown of CBP/p300 interacting coactivator with glutamic acid/aspartic acid-rich tail 2 (CITED2) increased colon cancer cell invasiveness in vitro. Gene expression profiling revealed that CITED2 knockdown induced matrix metalloproteinase-13 (MMP-13) gene expression in colon cancer cells. Butyrate, a naturally occurring HDAC inhibitor, induced CITED2 expression and downregulated MMP-13 expression in RKO cells. Additionally, ectopic expression of CITED2 arrested RKO cell growth. Thus, CITED2 regulates colon cancer invasion and might be a target for HDAC inhibitor-based intervention of colon cancer.