6q24.1

ASD8,MRG-1,MRG1,P35SRJ,VSD2

Adrenocortical carcinoma

CITED2 is expressed in adrenocortical carcinomas as well as in the adrenocortical carcinoma cell line NCI-H295R. CITED2 is upregulated by bFGF, Forskolin, endothelial cell products and Angiotensin II in NCI-H295R cells (Haase et al., 2007; Romero et al., 2007; Haase et al., 2009). In part, CITED2-expression in adrenocortical carcinomas could be observed in close proximity to blood vessels (Haase et al., 2009).

Breast cancer

CITED2 is highly expressed in MDA-MB-231 invasive breast cancer cells which are resistant to TGF-beta mediated growth arrest. TGF-beta induced MDA-MB-231 cell invasion could be reduced by downregulation of CITED2 as an enhancer of metalloproteinase 9 (MMP9)-expression, suggesting a role for CITED2 during tumor invasion (Chou et al., 2005). In Fibroblasts and in breast cancer cells FOXO3a inhibits HIF-1 induced apoptosis via upregulation of CITED2 (Bakker et al., 2007). CITED2 was especially expressed in human breast cancer cell lines that form osteolytic metastases in animal models. Elevated expression of CITED2 could also be observed in invasive ductal carcinoma tissue samples and in breast cancer bone metastases in comparison to normal mammary epithelial tissues (Lau et al., 2010). A study from Agthoven et al., observed that high levels of CITED2 mRNA in oestrogen receptor-alpha positive breast tumors of lymph-node negative patients were associated with prolonged metastasis-free-survival. In the same study high levels of CITED2 mRNA were also associated with a favourable outcome in patients that have received Tamoxifen as a first line therapy (van Agthoven et al., 2009).

Colorectal cancer

In a human colorectal carcinoma cell line CITED2 is downregulated by Rac1, a protein that has been associated with tumor growth (Gomez del Pulgar et al., 2007). In the human colon cancer cell line RKO downregulation of CITED2 increased colon cancer cell invasivness and upregulated MMP-13 expression (Bai et al., 2007).

Esophageal cancer

CITED2 was downregulated in a well and a poorly differentiated esophageal cancer cell line after treatment with up to 8 Gy irradiation (Bo et al., 2004).

Leiomyoma

GnRHa therapy increased CITED2 expression in leiomyoma and myometrium. GnRHa therapy had a biphasic effect on CITED2 expression in primary cultures of myometrial smooth muscle cells and inhibits expression in primary cultures of leiomyoma smooth muscle cells (Luo et al., 2005b). Expression of CITED2 was downregulated by TGF-beta in primary cultures of myometrial and leiomyoma smooth muscle cells (Luo et al., 2005a).

CITED2 is downregulated in radiation-induced rat osteosarcoma as compared with normal osteoblasts (Daino et al., 2009). The analysis of radiation-induced rat osteosarcoma showed reduced mRNA and protein expression and suggests a role for CITED2 as a tumor supressor gene in osteosarcoma (Daino et al., 2009).

Ovarian carcinoma

CITED2 expression was significantly downregulated after silencing of the tumor susceptibility gene 101 protein (TSG101) in SKOV-3 ovarian cancer cells with elevated RAS activity. The downregulation of CITED2 went along with a decrease of cell viability (Young et al., 2007). Expression of CITED2 was elevated in the oxaliplatin resistant cell line KFR as compared with the oxaliplatin sensitive cell line KF-1. The downregulation of CITED2 in the platinum-resistent ovarian cancer cell line KFR enhances the cytotoxicity of platinum compounds to the KFR cell line (Yanangie et al., 2009).

Sarcoma

Ewings-Sarcoma show a 6-fold increase in CITED2-expression as compared with rhabdomyosarcoma (Baer et al., 2004).

Adrenal development and adrenocortical physiology

CITED2-null mice show adrenal agenesis indicating a role for CITED2 within adrenal development (Bamforth et al., 2001). At 8 weeks of gestation CITED2 could be detected especially within the definitive zone of the developing adrenal cortex (Haase et al., 2007). Following studies confirmed the expression of CITED2 during early human fetal adrenal gland development at 7 and 10 weeks of gestation (Ferraz-de-Souza et al., 2009). In mice CITED2 was expressed in the coelomic epithelium and in the nephrogenic mesenchyme at E10. At E12 CITED2 was highly expressed in the adrenal primordium and remained highly expressed in adrenocortical cells at E13.5 and later (Val et al., 2007). In mice CITED2 acts as a WT-1 co-factor to increase SF-1 levels in the adrenogonadal primordium to initiate adrenal development (Val et al., 2007). Other studies applying human NCI-H295R adrenal carcinoma cells demonstrate that SF-1 activates the CITED2-promoter (Ferraz-de-Souza et al., 2009). In human NCI-H295R cells CITED2-expression is regulated by basic fibroblast growth factor, endothelial cell products and is dependent on the MAPK-pathway (Haase et al., 2007; Haase et al., 2009). Forskolin could also be identified as a positive regulator of CITED2-expression in NCI-H295R cells (Haase et al., 2007; Romero et al., 2007). Angiotensin II upregulates CITED2-expression in NCI-H295R cells and CITED2 enhances the expression of steroidogenic enzymes such as 11-beta-Hydroxylase and Aldosterone-Synthase (Romero et al., 2007).

Congenital heart defects and cardiac septal defects

CITED2 -/- mice show cardiac malformations including ventricular and atrial septal defects, double-outlet right ventricle, overriding aorta, right sided aortic arches and persistent truncus arteriosus (Bamforth et al., 2001). Functional loss of CITED2 during transrepression of HIF-1 alpha has been suggested to be responsible for the observed phenotype (Yin et al., 2002). Aberrant signaling of the Nodal-Pitx2c pathway has also been linked to the cardiovascular defects observed in CITED2 -/- mice (Bamforth et al., 2004). Aberrant left-right patterning as well as direct loss of CITED2 in cardiac tissues has been associated with the defects in CITED2-null mice (Weninger et al., 2005). The cardiovascular defects seem to result from the disruption of left-right patterning in epiblast derivatives and from the malfunction of septation in the mesoderm (MacDonald et al., 2008).
Mutations of CITED2 in humans have been linked to cardiac septal defects and congenital heart defects (Sperling et al., 2005).

Exencephaly, neural crest defects and neurologic implications

CITED2-null mice show exencephaly, abnormal cranial ganglia, neural crest defects and increased apoptosis in the midbrain region (Bamforth et al., 2001). Exencephaly seem to arise from defective closure of the midbrain and hindbrain region, associated with a defective closure of the neural tube (Barbera et al., 2002). Apoptosis around the Forebrain-Midbrain-junction in the dorsal neuroectoderm was increased in CITED2 -/- mice and CITED2 was necessary for the survival of neuroepithelial cells (Barbera et al., 2002). The administration of folic acid significantly reduced exencephaly in CITED2-null mice (Barbera et al., 2002). Transient forebrain ischemia induced CITED2-expression in different brain regions including the piriform cortex and the dentate gyrus of the hippocampal region and it has been speculated if CITED2 protects from neuronal death under hypoxic conditions (Sun et al., 2006). However, other studies also demonstrate that CITED2-overexpression can promote cell death in cortical neurons of the mouse (Gonzales et al., 2008). CITED2 expression is increased after olfactory bulbectomy and may contribute to the phenotype of basal progenitor cells of the olfactory sensory neuron lineage in the mouse (Shetty et al., 2005). CITED2 was also identified as a neural activity-dependent transcription-factor in vivo and in vitro in rat cortical neurons (Sun et al., 2007).

Eye developement

CITED2 is necessary for the morphogenesis of the lens and for hyaloid vasculature formation (Chen et al., 2008). Selective deletion of CITED2 resulted in abnormal corneal epithelial differentiation, impaired wound healing and corneal neovascularization in older mice associated with decreased expression of Pax6 and Klf4 (Chen et al., 2009).

Fracture healing

CITED2 was identified as a negative regulator of fracture healing in rats and was inversly related to the expression of metalloproteinases (MMP-2, MMP-3, MMP-9, MMP-13), HIF-1a, VEGF, RANK-L, M-CSF and OPG (Lee et al., 2009).

Gonadal development

In CITED2 null mice XY-gonad development was delayed and testis structure was disorganized. In XX-gonads of CITED2 null mice cell migration was disturbed (Combes et al., 2009). CITED2 interacts with Wt1 and SF-1 in mice and increases Sry levels initiating testes development (Buaas et al., 2009).

Hematopoiesis

CITED2 is required for the regulation of hematopoeisis during embryogenesis in the murine fetal liver (Chen et al., 2007). CITED2 controls adult hematopoietic stem cell function via Ink4a/Arf and Trp53 (Kranc et al., 2009).

Liver development

CITED2 null mice show liver hypoplasia, increased apoptosis, disrupted sinusoidal architecture, disrupted cell-cell contacts, impaired lipid metabolism and gluconeogenesis. The observations have been linked to the role of CITED2 as a co-activator of HNF4alpha (Qu et al., 2007).

Lung development

CITED2 is required for fetal lung maturation. Terminal sac space and differentiation of alveolar epithelial cells Typ 1 and 2 is altered in CITED2 null lungs in mice (Xu et al., 2008). CITED2 is developmentally regulated in pulmonary artery smooth muscle cells in sheep with higher expression in the fetus compared with the adult (Resnik et al., 2007).