Partial rescue of defects in Cited2-deficient embryos by HIF-1alpha heterozygosity

Tetralogy of Fallot: Hypoxia, the villain of the story?

BACKGROUND

Tetralogy of Fallot (ToF) is a cyanotic congenital heart disease, composed of four malformations: persistent communication between the right and the left ventricle, pulmonary stenosis, overriding aorta, and right ventricle hypertrophy. The etiology of this disease is not entirely known as yet, but it has been proposed that the pathology has genetic components. During embryonic development, the fetus is exposed to a physiological hypoxia to facilitate the formation of blood vessels and blood cells through de novo processes.

METHODS

After researching scientific databases on the implications of oxygen on the normal and abnormal development of organs, especially the heart, we were able to propose that oxygen deprivation may be the cause of the disease.

RESULTS

During this period, the hypoxia-inducible factor is activated and triggers transcriptional responses that enable adaptation to the hypoxic environment through angiogenic activation. High levels of this protein can alter certain physiological pathways, such as those related to the vascular endothelial growth factor. Research has shown that prolonged oxygen deprivation during embryological development can lead to the occurrence of congenital heart diseases, such as ToF.

CONCLUSIONS

Studies using animal models have demonstrated that the deficiency or disruption of a protein called "CITED2," which plays an important role in cardiac morphogenesis and its loss, results in the alteration of pluripotent, cardiac, and neural lineage differentiation, thereby disrupting the normal development of the heart and other tissues.

Charting the Path: Navigating Embryonic Development to Potentially Safeguard against Congenital Heart Defects

Congenital heart diseases (CHDs) are structural or functional defects present at birth due to improper heart development. Current therapeutic approaches to treating severe CHDs are primarily palliative surgical interventions during the peri- or prenatal stages, when the heart has fully developed from faulty embryogenesis. However, earlier interventions during embryonic development have the potential for better outcomes, as demonstrated by fetal cardiac interventions performed in utero, which have shown improved neonatal and prenatal survival rates, as well as reduced lifelong morbidity. Extensive research on heart development has identified key steps, cellular players, and the intricate network of signaling pathways and transcription factors governing cardiogenesis. Additionally, some reports have indicated that certain adverse genetic and environmental conditions leading to heart malformations and embryonic death may be amendable through the activation of alternative mechanisms. This review first highlights key molecular and cellular processes involved in heart development. Subsequently, it explores the potential for future therapeutic strategies, targeting early embryonic stages, to prevent CHDs, through the delivery of biomolecules or exosomes to compensate for faulty cardiogenic mechanisms. Implementing such non-surgical interventions during early gestation may offer a prophylactic approach toward reducing the occurrence and severity of CHDs.

Targeting Endothelial HIF2α/ARNT Expression for Ischemic Heart Disease Therapy

Ischemic heart disease (IHD) is a major cause of mortality and morbidity worldwide, with novel therapeutic strategies urgently needed. Endothelial dysfunction is a hallmark of IHD, contributing to its development and progression. Hypoxia-inducible factors (HIFs) are transcription factors activated in response to low oxygen levels, playing crucial roles in various pathophysiological processes related to cardiovascular diseases. Among the HIF isoforms, HIF2α is predominantly expressed in cardiac vascular endothelial cells and has a key role in cardiovascular diseases. HIFβ, also known as ARNT, is the obligate binding partner of HIFα subunits and is necessary for HIFα's transcriptional activity. ARNT itself plays an essential role in the development of the cardiovascular system, regulating angiogenesis, limiting inflammatory cytokine production, and protecting against cardiomyopathy. This review provides an overview of the current understanding of HIF2α and ARNT signaling in endothelial cell function and dysfunction and their involvement in IHD pathogenesis. We highlight their roles in inflammation and maintaining the integrity of the endothelial barrier, as well as their potential as therapeutic targets for IHD.

Genetic Variants of CITED2 Gene Promoter in Human Atrial Septal Defects: Case-Control Study and Cellular Functional Verification

Atrial septal defect (ASD) is one of the most common forms of congenital heart disease (CHD). Genetic variants in the coding region of the CITED2 gene are known to be significantly correlated with CHD, but the role of variants in the promoter region of CITED2 is unknown. We investigated variants in the promoter of the CITED2 gene in 625 subjects (332 ASD and 293 healthy controls) through Sanger sequencing. Four variants in the CITED2 gene promoter were found only in eight ASD patients with zero occurrence in the control subjects (one case of g.4078A>C(rs1165649373), one case of g.4240C>A(rs1235857801), four cases of g.4935C>T(rs111470468), two cases of g.5027C>T(rs112831934)). Cellular functional analysis showed that these four variants significantly changed the transcriptional activity of the CITED2 gene promoter in HEK-293 and HL-1 cells. Electrophoretic mobility change assay results and JASPAR database analysis demonstrated that these variants created or destroyed a series of possible transcription factor binding sites, resulting in changes in the expression of CITED2 protein. We conclude that the variants of CITED2 promoter in ASD patients affect the transcriptional activity and are likely involved in the occurrence and development of ASD. These findings provide new perspectives on the pathogenesis and potential therapeutic insights of ASD.

Understanding p300-transcription factor interactions using sequence variation and hybridization

The hypoxic response is central to cell function and plays a significant role in the growth and survival of solid tumours. HIF-1 regulates the hypoxic response by activating over 100...

Genetic analysis of the CITED2 gene promoter in isolated and sporadic congenital ventricular septal defects

Ventricular septal defect (VSD) is the most common congenital heart defect. Previous studies have reported genetic variations in the encoding region of CITED2 highly associated with cardiac malformation but the role of CITED2 gene promoter variations in VSD patients has not yet been explored. We investigated the variation of CITED2 gene promoter and its impacts on gene promoter activity in the DNA of paediatric VSD patients. A total of seven variations were identified by Sanger sequencing in the CITED2 gene promoter region in 400 subjects, including 200 isolated and sporadic VSD patients and 200 healthy controls. Using dual-luciferase reporter assay, we found four of the 7 variations identified significantly decreased the transcriptional activity of the CITED2 gene promoter in HEK-293 cells (P < .05). Further, a bioinformatic analysis with the JASPAR databases was performed and a cluster of putative binding sites for transcription factors was created or disrupted by these variations, leading to low expression of CITED2 protein and development of VSD. Our study for the first time demonstrates genetic variations in the CITED2 gene promoter in the Han Chinese population and the role of these variations in the development of VSD, providing new insights into the aetiology of CHD.

The long and winding road of cardiomyocyte maturation

Knowledge about the molecular mechanisms regulating cardiomyocyte (CM) proliferation and differentiation has increased exponentially in recent years. Such insights together with the availability of more efficient protocols for generation of CMs from induced pluripotent stem cells (iPSCs) have raised expectations for new therapeutic strategies to treat congenital and non-congenital heart diseases. However, the poor regenerative potential of the postnatal heart and the incomplete maturation of iPSC-derived CMs represent important bottlenecks for such therapies in future years. CMs undergo dramatic changes at the doorstep between prenatal and postnatal life, including terminal cell cycle withdrawal, change in metabolism, and further specialization of the cellular machinery required for high-performance contraction. Here, we review recent insights into pre- and early postnatal developmental processes that regulate CM maturation, laying specific focus on genetic and metabolic pathways that control transition of CMs from the embryonic and perinatal to the fully mature adult CM state. We recapitulate the intrinsic features of CM maturation and highlight the importance of external factors, such as energy substrate availability and endocrine regulation in shaping postnatal CM development. We also address recent approaches to enhance maturation of iPSC-derived CMs in vitro, and summarize new discoveries that might provide useful tools for translational research on repair of the injured human heart.

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.

Generation of a hypoxia-sensing mouse model

Oxygen (O₂ ) homeostasis is essential to the metazoan life. O₂ -sensing or hypoxia-regulated molecular pathways are intimately involved in a wide range of critical cellular functions and cell survival from embryogenesis to adulthood. In this report, we have designed an innovative hypoxia sensor (O₂ CreER) based on the O₂ -dependent degradation domain of the hypoxia-inducible factor-1α and Cre recombinase. We have further generated a hypoxia-sensing mouse model, R26-O₂ CreER, by targeted insertion of the O₂ CreER-coding cassette in the ROSA26 locus. Using the ROSA^mTmG mouse strain as a reporter, we have found that this novel hypoxia-sensing mouse model can specifically identify hypoxic cells under the pathological condition of hind-limb ischemia in adult mice. This model can also label embryonic cells including vibrissal follicle cells in E13.5-E15.5 embryos. This novel mouse model offers a valuable genetic tool for the study of hypoxia and O₂ sensing in mammalian systems under both physiological and pathological conditions.

Novel Point Mutations of CITED2 Gene Are Associated with Non-familial Congenital Heart Disease (CHD) in Sporadic Pediatric Patients

CITED2 is a cardiac transcription factor that plays a critical role in cardiac development. Gene mutations in CITED2 lead to a series of cardiac malformations and congenital heart defects (CHD). Congenital heart disease generally refers to defects in the heart's structure or function and often seen in many forms such as ventricular septal defects (VSDs), atrial septal defects (ASDs), and tetralogy of Fallot (TOF). However, the mechanisms involved in these mutations are poorly understood. The aim of the present study was to evaluate the mutations of the CITED2 gene in pediatric patients with congenital heart defects. We studied the potential impact of sequence variations of the CITED2 gene in a cohort of 150 patients with non-familial CHD and 98 control individuals by polymerase chain reaction-single-stranded conformation polymorphism (PCR-SSCP) and subsequently direct sequencing. We identified seven novel CITED2 nucleotide changes. Four of these alterations were found in the coding region (c.716insG, c.389A>G, c.450G>C and c.512-538del27) and were only seen in our patients, and not detected in the control group. These mutations are leading to changes in the amino acid sequence in the position of p.Gly236fs, p.Asn125Ser, p.Gln145His, and p.Ser170-Gly178del, respectively. Other variations are located in the 5'UTR region of the gene (c.-43C>T, c.-64C>T and c.-90A>G). CITED2 gene mutations in control subjects were not observed. Our Bioinformatics assay results showed that these novel mutations alter the RNA folding, protein structure, and, therefore, probable effect on the protein function and may play a significant role in the development of congenital heart diseases.

Oxygen and lack of oxygen in fetal and placental development, feto-placental coupling, and congenital heart defects

Low oxygen concentration (hypoxia) is part of normal embryonic development, yet the situation is complex. Oxygen (O₂ ) is a janus gas with low levels signaling through hypoxia-inducible transcription factor (HIF) that are required for development of fetal and placental vasculature and fetal red blood cells. This results in coupling of fetus and mother around midgestation as a functional feto-placental unit (FPU) for O₂ transport, which is required for continued growth and development of the fetus. Defects in these processes may leave the developing fetus vulnerable to O₂ deprivation or other stressors during this critical midgestational transition when common septal and conotruncal heart defects (CHDs) are likely to arise. Recent human epidemiological and case-control studies support an association between placental dysfunction, manifest as early onset pre-eclampsia (PE) and increased serum bio-markers, and CHD. Animal studies support this association, in particular those using gene inactivation in the mouse. Sophisticated methods for gene inactivation, cell fate mapping, and a quantitative bio-reporter of O₂ concentration support the premise that hypoxic stress at critical stages of development leads to CHD. The secondary heart field contributing to the cardiac outlet is a key target, with activation of the un-folded protein response and abrogation of FGF signaling or precocious activation of a cardiomyocyte transcriptional program for differentiation, suggested as mechanisms. These studies provide a strong foundation for further study of feto-placental coupling and hypoxic stress in the genesis of human CHD.

Hypoxia Supports Epicardial Cell Differentiation in Vascular Smooth Muscle Cells through the Activation of the TGFβ Pathway

Epicardium-derived cells (EPDCs) are an important pool of multipotent cardiovascular progenitor cells. Through epithelial-to-mesenchymal-transition (EMT), EPDCs invade the subepicardium and myocardium and further differentiate into several cell types required for coronary vessel formation. We previously showed that epicardial hypoxia inducible factor (HIF) signaling mediates the invasion of vascular precursor cells critical for patterning the coronary vasculature. Here, we examine the regulatory role of hypoxia (1% oxygen) on EPDC differentiation into vascular smooth muscle cells (VSMCs). Results: Hypoxia stimulates EMT and enhances expression of several VSMC markers in mouse epicardial cell cultures. This stimulation is specifically blocked by inhibiting transforming growth factor-beta (TGFβ) receptor I. Further analyses indicated that hypoxia increases the expression level of TGFβ-1 ligand and phosphorylation of TGFβ receptor II, suggesting an indispensable role of the TGFβ pathway in hypoxia-stimulated VSMC differentiation. We further demonstrate that the non-canonical RhoA/Rho kinase (ROCK) pathway acts as the main downstream effector of TGFβ to modulate hypoxia’s effect on VSMC differentiation. Conclusion: Our results reveal a novel role of epicardial HIF in mediating coronary vasculogenesis by promoting their differentiation into VSMCs through noncanonical TGFβ signaling. These data elucidate that patterning of the coronary vasculature is influenced by epicardial hypoxic signals.

CITED2 Mutations in Conserved Regions Contribute to Conotruncal Heart Defects in Chinese Children

Conotruncal heart defects (CTDs) are severe malformations of outflow tract with heterogeneous morphology. Several missense variants of CITED2 have been identified to cause CTDs in recent researches. In this study, we screened the coding regions of CITED2 in 605 Chinese children with CTDs and found two possible pathogenic mutant sites: p.Q117L and p.T257A, both located in the conserved regions of CITED2. Then, we investigated the biological and functional alterations of them. Western blotting showed low level of protein expression of mutant Q117 and T257A compared with wild-type CITED2. Dual-luciferase reporter assay demonstrated that mutant Q117 and T257A decreased the ability of CITED2 to modulate the expression of paired-like homeodomain transcription factor 2 gamma (PITX2C), which are closely related to cardiac growth and left-right patterning. Meanwhile, T257A also exhibited impaired ability to mediate vascular endothelial growth factor expression, another gene closely associated with the normal development of cardiovascular system. Three-dimensional molecular conformation showed reduced hydrogen bond between Asp254 and mutant Thr257, indicating the weakened stability and binding ability of CITED2. All these results suggest that CITED2 mutations in conserved regions lead to disease-causing biological and functional changes and may contribute to the occurrence of CTDs.

[Expression and significance of hypoxia-inducible factor 1α in endplate chondrocytes of rats]

Objective

To explore the expression and significance of hypoxia-inducible factor 1α (HIF-1α) in endplate chondrocytes, and to study the relations between HIF-1α expression and endplate chondrocytes apoptosis.

Methods

Eight Sprague Dawley rats were selected to obtain the L _1-5 intervertebral disc endplate; the endplate chondrocytes were isolated by enzyme digestion method, and the endplate chondrocytes at passage 3 were cultured under 20% O ₂ condition (group A), and under 0.5% O ₂ condition (group B). Cell morphology was observed by inverted phase contrast microscope and cell apoptosis was detected using flow cytometry after cultured for 24 hours; the mRNA expression of HIF-1α was detected by real-time fluorescent quantitative PCR, the protein expressions of HIF-1α, Bax, and Bcl-2 by Western blot. Gene clone technology to design and synthesize two siRNAs based on the sequence of HIF-1α mRNA. HIF-1α specific RNAi sequence compound was constructed and transfected into cells. The transfected endplate chondrocytes at passage 3 were cultured under 0.5% O ₂ condition in group C and group D (HIF-1α gene was silenced). After cultured for 24 hours, cells were observed via immunofluorescence staining of HIF-1α, and cell apoptosis was detected using flow cytometry. Meanwhile, the mRNA expressions of HIF-1α, collagen type II (COL II), Aggrecan, and SOX9 were detected by real-time fluorescent quantitative PCR, and the protein expressions of HIF-1α, Bax, and Bcl-2 by Western blot.

Results

At 24 hours after culture, small amount of vacuoles necrotic cells could be observed in group A and group B; there was no significant difference in apoptosis rate between groups A and B ( t=1.026, P=0.471), and HIF-1α mRNA and protein expressions in group B were significantly higher than those in group A ( t=22.672, P=0.015; t=18.396, P=0.013), but, there was no significant difference in protein expressions of Bax and Bcl-2 between groups A and B ( t=0.594, P=0.781; t=1.251, P=0.342). The number of vacuolar necrosis cells in group D was significantly higher than that in group C, and HIF-1α positive cells were observed in group D. The apoptosis rate of group D was significantly higher than that of group C ( t=27.143, P=0.002). The mRNA expressions of HIF-1α, COL II, Aggrecan, and SOX9 in group D were significantly lower than those in group C ( t=21.097, P=0.015; t=34.829, P=0.002; t=18.673, P=0.022; t=31.949, P=0.007). The protein expressions of HIF-1α and Bcl-2 in group D were significantly lower than those in group C ( t=37.648, P=0.006; t=16.729, P=0.036), but the protein expression of Bax in group D was significantly higher than that in group C ( t=25.583, P=0.011).

Conclusion

HIF-1α mRNA expression is up-regulated under hypoxia condition, which will increase the hypoxia tolerance of endplate chondrocytes. Cell apoptosis is suppressed by the activation of HIF-1α in endplate chondrocytes under hypoxia condition.

Functional Analysis of Two Novel Mutations in TWIST1 Protein Motifs Found in Ventricular Septal Defect Patients

The aim of this study was to investigate the possible genetic effect of sequence variations in TWIST1 on the pathogenesis of ventricular septal defect in humans. We examined the coding region of TWIST1 in a cohort of 196 Chinese people with non-syndromic ventricular septal defect patients and 200 healthy individuals as the controls. We identified two novel potential disease-associated mutations, NM_000474.3:c.247G>A (G83S) and NM_000474.3:c.283A>G (S95G). Both of them were identified for the first time and were not observed in the 200 controls without congenital heart disease. Using a dual-luciferase reporter assay, we showed that both of the mutations significantly down-regulated the repressive effect of TWIST1 on the E-cadherin promoter. Furthermore, a mammalian two-hybrid assay showed that both of the mutations significantly affected the interaction between TWIST1 and KAT2B. New mutations in the transcription factor TWIST1 that affect protein function were identified in 1.0 % (2/196) of Chinese patients with ventricular septal defect. Our data show, for the first time, that TWIST1 has a potential causative effect on the development of ventricular septal defect.

HIF hydroxylase pathways in cardiovascular physiology and medicine

Hypoxia inducible factors (HIFs) are α/β heterodimeric transcription factors that direct multiple cellular and systemic responses in response to changes in oxygen availability. The oxygen sensitive signal is generated by a series of iron and 2-oxoglutarate-dependent dioxygenases that catalyze post-translational hydroxylation of specific prolyl and asparaginyl residues in HIFα subunits and thereby promote their destruction and inactivation in the presence of oxygen. In hypoxia, these processes are suppressed allowing HIF to activate a massive transcriptional cascade. Elucidation of these pathways has opened several new fields of cardiovascular research. Here, we review the role of HIF hydroxylase pathways in cardiac development and in cardiovascular control. We also consider the current status, opportunities, and challenges of therapeutic modulation of HIF hydroxylases in the therapy of cardiovascular disease.

FBXL5 modulates HIF-1α transcriptional activity by degradation of CITED2

CITED2 is a ubiquitously expressed nuclear protein exhibiting a high affinity for the cysteine-histidine-rich domain 1 (CH1) of the transcriptional co-activators CBP/p300. CITED2 is particularly efficient in the inhibition of the hypoxia-inducible factor-1α (HIF-1α) dependent transcription by competing with it for the interaction with the CH1 domain. Here we report a direct and specific interaction between CITED2 and the F-box and leucine rich repeat protein 5 (FBXL5), a substrate adaptor protein which is part of E3 ubiquitin ligase complexes mediating protein degradation by the proteasome. We demonstrated that depletion of FBXL5 by RNA interference led to an increase of CITED2 protein levels. Conversely, overexpression of FBXL5 caused the decrease of CITED2 protein levels in a proteasome-dependent manner, and impaired the interaction between CITED2 and the CH1 domain of p300 in living cells. In undifferentiated mouse embryonic stem cells, the overexpression of FBXL5 also reduced Cited2 protein levels. Finally, we evidenced that FBXL5 overexpression and the consequent degradation of CITED2 enabled the transcriptional activity of the N-terminal transactivation domain of HIF-1α. Collectively, our results highlighted a novel molecular interaction between CITED2 and FBXL5, which might regulate the steady state CITED2 protein levels and contribute to the modulation of gene expression by HIF-1α.

Connecting the coronaries: how the coronary plexus develops and is functionalized

The establishment of the coronary circulation is one of the final critical steps during heart development. Despite decades of research, our understanding of how the coronary vasculature develops and connects to the aorta remains limited. This review serves two specific purposes: it addresses recent advances in understanding the origin of the coronary endothelium, and it then focuses on the last crucial step of coronary vasculature development, the connection of the coronary plexus to the aorta. The chick and quail animal models have yielded most of the information for how these connections form, starting with a fine network of vessels that penetrate the aorta and coalesce to form two distinct ostia. Studies in mouse and rat confirm that at least some of these steps are conserved in mammals, but gaps still exist in our understanding of mammalian coronary ostia formation. The signaling cues necessary to guide the coronary plexus to the aorta are also incompletely understood. Hypoxia-inducible transcription factor-1 and its downstream targets are among the few identified genes that promote the formation of the coronary stems. Together, this review summarizes our current knowledge of coronary vascular formation and highlights the significant gaps that remain. In addition, it highlights some of the coronary artery anomalies known to affect human health, demonstrating that even seemingly subtle defects arising from incorrect coronary plexus formation can result in significant health crises.

Vulnerability of the developing heart to oxygen deprivation as a cause of congenital heart defects

Background

The heart develops under reduced and varying oxygen concentrations, yet there is little understanding of oxygen metabolism in the normal and mal‐development of the heart. Here we used a novel reagent, the ODD‐Luc hypoxia reporter mouse (oxygen degradation domain, ODD) of Hif‐1α fused to Luciferase (Luc), to assay the activity of the oxygen sensor, prolyl hydroxylase, and oxygen reserve, in the developing heart. We tested the role of hypoxia‐dependent responses in heart development by targeted inactivation of Hif‐1α.

Methods and Results

ODD‐Luciferase activity was 14‐fold higher in mouse embryonic day 10.5 (E10.5) versus adult heart and liver tissue lysates. ODD‐Luc activity decreased in 2 stages, the first corresponding with the formation of a functional cardiovascular system for oxygen delivery at E15.5, and the second after birth consistent with complete oxygenation of the blood and tissues. Reduction of maternal inspired oxygen to 8% for 4 hours caused minimal induction of luciferase activity in the maternal tissues but robust induction in the embryonic tissues in proportion to the basal activity, indicating a lack of oxygen reserve, and corresponding induction of a hypoxia‐dependent gene program. Bioluminescent imaging of intact embryos demonstrated highest activity in the outflow portion of the E13.5 heart. Hif‐1α inactivation or prolonged hypoxia caused outflow and septation defects only when targeted to this specific developmental window.

Conclusions

Low oxygen concentrations and lack of oxygen reserve during a critical phase of heart organogenesis may provide a basis for vulnerability to the development of common septation and conotruncal heart defects.

Variations of CITED2 are associated with congenital heart disease (CHD) in Chinese population

CITED2 was identified as a cardiac transcription factor which is essential to the heart development. Cited2-deficient mice showed cardiac malformations, adrenal agenesis and neural crest defects. To explore the potential impact of mutations in CITED2 on congenital heart disease (CHD) in humans, we screened the coding region of CITED2 in a total of 700 Chinese people with congenital heart disease and 250 healthy individuals as controls. We found five potential disease-causing mutations, p.P140S, p.S183L, p.S196G, p.Ser161delAGC and p. Ser192_Gly193delAGCGGC. Two mammalian two-hybrid assays showed that the last four mutations significantly affected the interaction between p300CH1 and CITED2 or HIF1A. Further studies showed that four CITED2 mutations recovered the promoter activity of VEGF by decreasing its competitiveness with HIF1A for binding to p300CH1 and three mutations decreased the consociation of TFAP2C and CITED2 in the transactivation of PITX2C. Both VEGF and PITX2C play very important roles in cardiac development. In conclusion, we demonstrated that CITED2 has a potential causative impact on congenital heart disease.

Time-lapse imaging of cell cycle dynamics during development in living cardiomyocyte

Mammalian cardiomyocytes withdraw from the cell cycle shortly after birth, although it remains unclear how cardiomyocyte cell cycles behave during development. Compared to conventional immunohistochemistry in static observation, time-lapse imaging can reveal comprehensive data in hard-to-understand biological phenomenon. However, there are no reports of an established protocol of successful time-lapse imaging in mammalian heart. Thus, it is valuable to establish a time-lapse imaging system to enable the observation of cell cycle dynamics in living murine cardiomyocytes. This study sought to establish time-lapse imaging of murine heart to study cardiomyocyte cell cycle behavior. The Fucci (fluorescent ubiquitination-based cell cycle indicator) system can effectively label individual G1, S/G2/M, and G1/S-transition phase nuclei red, green and yellow, respectively, in living mammalian cells, and could therefore be useful to visualize the real-time cell cycle transitions in living murine heart. To establish a similar system for time-lapse imaging of murine heart, we first developed an ex vivo culture system, with the culture conditions determined in terms of sample state, serum concentration, and oxygen concentration. The optimal condition (slice culture, oxygen concentration 20%, serum concentration 10%) successfully mimicked physiological cardiomyocyte proliferation in vivo. Time-lapse imaging of cardiac slices from E11.5, E14.5, E18.5, and P1 Fucci-expressing transgenic mice revealed an elongated S/G2/M phase in cardiomyocytes during development. Our time-lapse imaging of murine heart revealed a gradual elongation of the S/G2/M phase during development in living cardiomyocytes.

Cited2, a transcriptional modulator protein, regulates metabolism in murine embryonic stem cells

CREB-binding protein (CBP)/p300 interacting transactivator with glutamic acid (Glu) and aspartic acid (Asp)-tail 2 (Cited2) was recently shown to be essential for gluconeogenesis in the adult mouse. The metabolic function of Cited2 in mouse embryonic stem cells (mESCs) remains elusive. In the current study, the metabolism of glucose was investigated in mESCs, which contained a deletion in the gene for Cited2 (Cited2(Δ/-)). Compared with its parental wild type counterpart, Cited2(Δ/-) ESCs have enhanced glycolysis, alternations in mitochondria morphology, reduced glucose oxidation, and decreased ATP content. Cited2 is recruited to the hexokinase 1 (HK1) gene promoter to regulate transcription of HK1, which coordinates glucose metabolism in wild type ESCs. Reduced glucose oxidation and enhanced glycolytic activity in Cited2(Δ/-) ESCs correlates with defective differentiation during hypoxia, which is reflected in an increased expression of pluripotency marker (Oct4) and epiblast marker (Fgf5) and decreased expression of lineage specification markers (T, Gata-6, and Cdx2). Knockdown of hypoxia inducible factor-1α in Cited2(Δ/-) ESCs re-initiates the expression of differentiation markers T and Gata-6. Taken together, a deletion of Cited2 in mESCs results in abnormal mitochondrial morphology and impaired glucose metabolism, which correlates with a defective cell fate decision.

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.

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.

Increased susceptibility of HIF-1α heterozygous-null mice to cardiovascular malformations associated with maternal diabetes

Cardiovascular malformations are the most common manifestation of diabetic embryopathy. The molecular mechanisms underlying the teratogenic effect of maternal diabetes have not been fully elucidated. Using genome-wide expression profiling, we previously demonstrated that exposure to maternal diabetes resulted in dysregulation of the hypoxia-inducible factor 1 (HIF-1) pathway in the developing embryo. We thus considered a possible link between HIF-1-regulated pathways and the development of congenital malformations. HIF-1α heterozygous-null (Hif1a(+/-)) and wild type (Wt) littermate embryos were exposed to the intrauterine environment of a diabetic mother to analyze the frequency and morphology of congenital defects, and assess gene expression changes in Wt and Hif1a(+/-) embryos. We observed a decreased number of embryos per litter and an increased incidence of heart malformations, including atrioventricular septal defects and reduced myocardial mass, in diabetes-exposed Hif1a(+/-) embryos as compared to Wt embryos. We also detected significant differences in the expression of key cardiac transcription factors, including Nkx2.5, Tbx5, and Mef2C, in diabetes-exposed Hif1a(+/-) embryonic hearts compared to Wt littermates. Thus, partial global HIF-1α deficiency alters gene expression in the developing heart and increases susceptibility to congenital defects in a mouse model of diabetic pregnancy.

Cited2 gene controls pluripotency and cardiomyocyte differentiation of murine embryonic stem cells through Oct4 gene

Cited2 (CBP/p300-interacting transactivator with glutamic acid (E)/aspartic acid (D)-rich tail 2) is a transcriptional modulator critical for the development of multiple organs. Although many Cited2-mediated phenotypes and molecular events have been well characterized using in vivo genetic murine models, Cited2-directed cell fate decision in embryonic stem cells (ESCs) remains elusive. In this study, we examined the role of Cited2 in the maintenance of stemness and pluripotency of murine ESCs by a gene-targeting approach. Cited2 knock-out (Cited2(Δ/-), KO) ESCs display defective differentiation. Loss of Cited2 in differentiating ESCs results in delayed silencing of the genes involved in the maintenance of pluripotency and self-renewal of stem cells (Oct4, Klf4, Sox2, and c-Myc) and the disturbance in cardiomyocyte, hematopoietic, and neuronal differentiation. In addition, Cited2 KO ESCs experience a delayed induction of cardiomyocyte differentiation-associated proteins, NFAT3 (along with the reduced expression of NFAT3 target genes, Nkx2.5 and β-MHC), N-cadherin, and smooth muscle actin. CITED2 is recruited to the Oct4 promoter to regulate its expression during early ESC differentiation. This is the first demonstration that Cited2 controls ESC pluripotency and differentiation via direct regulation of Oct4 gene expression.

Four-and-a-half LIM domain proteins inhibit transactivation by hypoxia-inducible factor 1

Hypoxia-inducible factor 1 (HIF-1) is a transcription factor that promotes angiogenesis, metabolic reprogramming, and other critical aspects of cancer biology. The four-and-a-half LIM domain (FHL) proteins are a family of LIM domain-only proteins implicated in transcriptional regulation and suppression of tumor growth. Here we describe functional interactions between the FHL proteins and HIF-1. FHL1-3 inhibit HIF-1 transcriptional activity and HIF-1α transactivation domain function by oxygen-independent mechanisms. FHL2 directly interacts with HIF-1α to repress transcriptional activity. FHL1 binds to the p300/CBP co-activators and disrupts binding with HIF-1α. FHL3 does not bind to HIF-1α or p300, indicating that it regulates transactivation by a novel molecular mechanism. Expression of the FHL proteins increased upon HIF-1α induction, suggesting the existence of a feedback loop. These results identify FHL proteins as negative regulators of HIF-1 activity, which may provide a mechanism by which they suppress tumor growth.

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.

Optical coherence tomography captures rapid hemodynamic responses to acute hypoxia in the cardiovascular system of early embryos

BACKGROUND

The trajectory to heart defects may start in tubular and looping heart stages when detailed analysis of form and function is difficult by currently available methods. We used a novel method, Doppler optical coherence tomography (OCT), to follow changes in cardiovascular function in quail embryos during acute hypoxic stress. Chronic fetal hypoxia is a known risk factor for congenital heart diseases (CHDs). Decreased fetal heart rates during maternal obstructive sleep apnea suggest that studying fetal heart responses under acute hypoxia is warranted.

RESULTS

We captured responses to hypoxia at the critical looping heart stages. Doppler OCT revealed detailed vitelline arterial pulsed Doppler waveforms. Embryos tolerated 1 hr of hypoxia (5%, 10%, or 15% O(2) ), but exhibited changes including decreased systolic and increased diastolic duration in 5 min. After 5 min, slower heart rates, arrhythmic events and an increase in retrograde blood flow were observed. These changes suggested slower filling of the heart, which was confirmed by four-dimensional Doppler imaging of the heart itself.

CONCLUSIONS

Doppler OCT is well suited for rapid noninvasive screening for functional changes in avian embryos under near physiological conditions. Analysis of the accessible vitelline artery sensitively reflected changes in heart function and can be used for rapid screening. Acute hypoxia caused rapid hemodynamic changes in looping hearts and may be a concern for increased CHD risk.

Pathophysiological response to hypoxia - from the molecular mechanisms of malady to drug discovery:inflammatory responses of hypoxia-inducible factor 1α (HIF-1α) in T cells observed in development of vascular remodeling

Recent studies have shown that the cellular immune response to the hypoxic microenvironment constructed by vascular remodeling development modulates the resulting pathologic alterations. A major mechanism mediating adaptive responses to reduced oxygen availability is the regulation of transcription by hypoxia-inducible factor 1 (HIF-1). Impairment of HIF-1-dependent inflammatory responses in T cells causes an augmented vascular remodeling induced by arterial injury, which is shown as prominent neointimal hyperplasia and increase in infiltration of inflammatory cells at the adventitia in mice lacking Hif-1α specifically in T cells. Studies to clarify the mechanism of augmented vascular remodeling in the mutant mice have shown enhanced production of cytokines in activated T cells and augmented antibody production in response to a T-dependent antigen in the mutant mice. This minireview shows that HIF-1α in T cells plays a crucial role in vascular inflammation and remodeling in response to cuff injury as a negative regulator of the T cell-mediated immune response and suggests potential new therapeutic strategies that target HIF-1α.

The role of hypoxia in development of the Mammalian embryo

Hypoxia inducible factor (HIF) is a transcription factor that acts in low-oxygen conditions. The cellular response to HIF activation is transcriptional upregulation of a large group of genes. Some target genes promote anaerobic metabolism to reduce oxygen consumption, while others "alleviate" hypoxia by acting non-cell-autonomously to extend and modify the surrounding vasculature. Although hypoxia is often thought of as being a pathological phenomenon, the mammalian embryo in fact develops in a low-oxygen environment, and in this context HIF has additional responsibilities. This review describes how low oxygen and HIF affect gene expression, cell behavior, and ultimately morphogenesis of the embryo and placenta.

Altered hypoxia-inducible factor-1 alpha expression levels correlate with coronary vessel anomalies

The outflow tract myocardium and other regions corresponding to the location of the major coronary vessels of the developing chicken heart, display a high level of hypoxia as assessed by the hypoxia indicator EF5. The EF5-positive tissues were also specifically positive for nuclear-localized hypoxia inducible factor-1 alpha (HIF-1alpha), the oxygen-sensitive component of the hypoxia inducible factor-1 (HIF-1) heterodimer. This led to our hypothesis that there is a "template" of hypoxic tissue that determines the stereotyped pattern of the major coronary vessels. In this study, we disturbed this template by altering ambient oxygen levels (hypoxia 15%; hyperoxia 75-40%) during the early phases of avian coronary vessel development, in order to alter tissue hypoxia, HIF-1alpha protein expression, and its downstream target genes without high mortality. We also altered HIF-1alpha gene expression in the embryonic outflow tract cardiomyocytes by injecting an adenovirus containing a constitutively active form of HIF-1alpha (AdCA5). We assayed for coronary anomalies using anti-alpha-smooth muscle actin immunohistology. When incubated under abnormal oxygen levels or injected with a low titer of the AdCA5, coronary arteries displayed deviations from their normal proximal connections to the aorta. These deviations were similar to known clinical anomalies of coronary arteries. These findings indicated that developing coronary vessels may be subject to a level of regulation that is dependent on differential oxygen levels within cardiac tissues and subsequent HIF-1 regulation of gene expression.

Regulation of oxygen homeostasis by hypoxia-inducible factor 1

Metazoan organisms are dependent on a continuous supply of O(2) for survival. Hypoxia-inducible factor 1 (HIF-1) is a transcription factor that regulates oxygen homeostasis and plays key roles in development, physiology, and disease. HIF-1 activity is induced in response to continuous hypoxia, intermittent hypoxia, growth factor stimulation, and Ca(2+) signaling. HIF-1 mediates adaptive responses to hypoxia, including erythropoiesis, angiogenesis, and metabolic reprogramming. In each case, HIF-1 regulates the expression of multiple genes encoding key components of the response pathway. HIF-1 also mediates maladaptive responses to chronic continuous and intermittent hypoxia, which underlie the development of pulmonary and systemic hypertension, respectively.

Expression of active Notch1 in avian coronary development

Notch1 is an important regulator of intercellular interactions in cardiovascular development. We show that the nuclear-localized, cleaved and active form of Notch1, the Notch1 intracellular domain (N1ICD), appeared in mesothelial cells of the pro-epicardium during epicardial formation at looped heart stages. N1ICD was also present in mesothelial cells and mesenchymal cells specifically within the epicardium at sulcus regions. N1ICD-positive endothelial cells were detected within the nascent vessel plexus at the atrioventricular junction and within the compact myocardium (Hamburger and Hamilton stage [HH] 25-HH30). The endothelial cells expressing N1ICD were surrounded by N1ICD-positive smooth muscle cells after coronary orifice formation (HH32-HH35), while N1ICD expression was absent in the mesenchymal and mesothelial cells surrounding mature coronary vessels. We propose that differential activation of the hypoxia/HIF1-VEGF-Notch pathway may play a role in epicardial cell interactions that promote epicardial epithelial/mesenchymal transition and coronary progenitor cell differentiation during epicardial development and coronary vasculogenesis in particularly hypoxic sulcus regions.

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.

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.

FOXO3a is activated in response to hypoxic stress and inhibits HIF1-induced apoptosis via regulation of CITED2

FOXO transcription factors are important regulators of cell survival in response to a variety of stress stimuli, among which are oxidative stress, DNA damage, and nutrient deprivation. Here we report a role for FOXO3a under conditions of hypoxic stress. In response to hypoxia, FOXO3a transcript levels accumulate in an HIF1-dependent way, resulting in enhanced FOXO3a activity. We show that transcription of CITED2, a transcriptional cofactor that functions in a negative feedback loop to control HIF1 activity, is induced by FOXO3a during hypoxia. In fibroblasts as well as in breast cancer cells, FOXO3a inhibits HIF1-induced apoptosis by stimulating the transcription of CITED2, which results in reduced expression of the proapoptotic HIF1 target genes NIX and RTP801. Thus, by fine-tuning HIF1 activity, FOXO3a plays an important role in the survival response of normal and cancer cells in response to hypoxic stress.

Developmental regulation of hypoxia-inducible factor 1 and prolyl-hydroxylases in pulmonary vascular smooth muscle cells

The transcriptional machinery involved in the transition of an infant from intrauterine to air-breathing life is developmentally regulated, as the fetus and adult manifest differential genetic expression. The low oxygen (O(2)) environment of the mammalian fetus and the increase in O(2) tension that occurs at birth may account for the developmentally regulated alterations in gene expression. We tested the hypothesis that hypoxia-inducible factor 1 (HIF-1) expression, an O(2)-sensitive transcription factor, is developmentally regulated. We found that in fetal pulmonary artery (PA) smooth muscle cells (SMC), fetal HIF-1 protein levels were O(2)-insensitive, whereas in adult PA SMC, hypoxia increased HIF-1 protein expression. Surprisingly, hypoxia increased HIF-1 mRNA expression in fetal, but not in adult, PA SMC. HIF-1 degradation and transcriptional activity is contingent on prolyl- and asparagyl-hydroxylases. To determine whether developmental differences in O(2) sensitivity or expression of these enzymes accounts for the divergence of HIF-1 sensitivity between fetus and adult, we studied the expression of the three most well characterized prolyl-hydroxylases, PHD1, PHD2, and PHD3, and the expression of regulators of HIF-1 transcriptional activity, asparagyl-hydroxylase, factor inhibiting HIF, and the oncogenic factor, CITED2 (CREB-binding protein/p300 interacting transactivator with ED-rich tail). We found that, as in the case of HIF-1, these genes are differentially regulated in the fetus, enabling the mammalian fetus to thrive in the low O(2) tension intrauterine environment even while rendering a newborn infant uniquely well adapted to respond to the acute increase in O(2) tension that occurs at birth.

CITED2 mediates the paradoxical responses of HIF-1alpha to proteasome inhibition

Hypoxia-inducible factor-1alpha (HIF-1alpha) is destabilized via the ubiquitin-proteasome system. Thus HIF-1alpha expression is robustly upregulated by proteasome inhibition, but paradoxically its activity is reduced. In the present study, we investigated the mechanism underlying the paradoxical response of HIF-1alpha to proteasome inhibition. In both Hep3B and HEK293 cells, a proteasome inhibitor MG132 noticeably attenuated hypoxic induction of erythropoietin and VEGF mRNAs. MG132 inactivated HIF-1alpha C-terminal transactivation domain (CAD), independently of factor inhibiting HIF-1 (FIH) and inhibited p300 recruitment by HIF-1alpha. We next tested the possibility that CITED2 is involved in the HIF-1 inactivation. CITED2 was found to be degraded via the ubiquitin-proteasome system and thus was stabilized by proteasome inhibition. Both the activity and the p300 binding of HIF-1alpha were inhibited by CITED2 expression and recovered by CITED2 siRNA in the presence of MG132. These results suggest that CITED2 is stabilized by proteasome inhibition and inactivates HIF-1 by interfering with the HIF-1alpha-p300 interaction. This may be an important mode-of-action for proteasome inhibition-based cancer therapy.

Cited2 is required for normal hematopoiesis in the murine fetal liver

Cited2 (cAMP-responsive elementbinding protein [CBP]/p300-interacting transactivators with glutamic acid [E] and aspartic acid [D]-rich tail 2) is a newly identified transcriptional modulator. Knockout of the Cited2 gene results in embryonic lethality with embryos manifesting heart and neural tube defects. Cited2-/- fetal liver displayed significant reduction in the numbers of Lin(-)c-Kit+Sca-1+ cells, Lin(-)c-Kit+ cells, and progenitor cells of different lineages. Fetal liver cells from Cited2-/- embryos gave rise to markedly reduced number of colonies in the colony-forming unit assay. Primary and secondary transplantation studies showed significantly compromised reconstitution of T-lymphoid, B-lymphoid, and myeloid lineages in mice that received a transplant of Cited2-/- fetal liver cells. Competitive reconstitution experiments further showed that fetal liver hematopoietic stem cell (HSC) function is severely impaired due to Cited2 deficiency. Microarray analysis showed decreased expression of Wnt5a and a panel of myeloid molecular markers such as PRTN3, MPO, Neutrophil elastase, Cathepsin G, and Eosinophil peroxidase in Cited2-/- fetal livers. Decreased expression of Bmi-1, Notch1, LEF-1, Mcl-1, and GATA2 was also observed in Cited2-/- Lin(-)c-Kit+ cells. The present study uncovers for the first time a novel role of Cited2 in the maintenance of hematopoietic homeostasis during embryogenesis and thus provides new insights into the molecular regulation of hematopoietic development.