Jae Mi Suh

The expression pattern of nuclear receptors during cerebellar development

The cerebellum is essential for fine control of movement and posture, and it has been a useful model for studying many aspects of neural development because of its relatively simple anatomy and developmental program. However, the roles of nuclear receptors (NRs) underlying formation of the cerebellum and maintenance of cerebellar functions are still poorly characterized. As a contribution to the Nuclear Receptor Signaling Atlas (NURSA), we employed immunohistochemistry to investigate the expression pattern of 18 NRs in the cerebellum. Ten receptors were demonstrated to be expressed in the postnatal day 21 (P21) cerebellum. Among them, five receptors (COUP‐TFI, COUP‐TFII, RORα, ERβ, and ERRγ) were expressed at all stages (embryonic stage, P0, P7, and P21) examined. Interestingly, COUP‐TFI and COUP‐TFII show differential anterior‐posterior expression patterns during cerebellar development. Taken together, our results suggest that members of the nuclear receptor superfamily might play importantly physiological roles in the cerebellum. Developmental Dynamics 236:810–820, 2007.

COUP-TFII is essential for metanephric mesenchyme formation and kidney precursor cell survival

Development of the metanephric kidney in mammals requires complex reciprocal tissue interactions between the ureteric epithelium and the mesenchyme. It is believed that Gdnf, produced in the metanephric mesenchyme, activates Ret signaling in the Wolffian duct to initiate the formation of the metanephros. However, the molecular mechanism for induction of Gdnf in the metanephric mesenchyme is not completely defined. Previous studies demonstrated that during the early stages of kidney development, loss of Osr1, Eya1, Pax2 or Wt1 gene function in the metanephric mesenchyme compromises the formation of the kidney. Moreover, it has been shown that the Hox11-Eya1-Pax2 complex activates the expression of Six2 and Gdnf in the metanephric mesenchyme to drive nephrogenesis. Here, we demonstrate that the orphan nuclear receptor chicken ovalbumin upstream promoter transcription factor II (COUP-TFII, also known as Nr2f2) is required for the specification of the metanephric mesenchyme. Deletion of COUP-TFII at E7.5 results in improper differentiation of the metanephric mesenchyme and absence of essential developmental regulators, such as Eya1, Six2, Pax2 and Gdnf. Importantly, we show that COUP-TFII directly regulates the expression of both Eya1 and Wt1 in the metanephric mesenchyme. Our findings reveal, for the first time, that COUP-TFII plays a central role in the specification of metanephric fate and in the maintenance of metanephric mesenchyme proliferation and survival by acting as a crucial regulator of Eya1 and Wt1 expression.

Thyrotropin-Mediated Repression of Class II Trans-Activator Expression in Thyroid Cells: Involvement of STAT3 and Suppressor of Cytokine Signaling

It has been suggested that class I and class II MHC are contributing factors for numerous diseases including autoimmune thyroid diseases, type 1 diabetes, rheumatoid arthritis, Alzheimer’s disease, and multiple sclerosis. The class II trans-activator (CIITA), which is a non-DNA-binding regulator of class II MHC transcription, regulates the constitutive and inducible expression of the class I and class II genes. FRTL-5 thyroid cells incubated in the presence of IFN-γ have a significantly higher level of cell surface rat MHC class II RTI.B. However, the IFN-γ-induced RT1.B expression was suppressed significantly in cells incubated in the presence of thyrotropin. Thyrotropin (TSH) represses IFN-γ-induced CIITA expression by inhibiting type IV CIITA promoter activity through the suppression of STAT1 activation and IFN regulatory factor 1 induction. This study found that TSH induces transcriptional activation of the STAT3 gene through the phosphorylation of STAT3 and CREB activation. TSH induces SOCS-1 and SOCS-3, and TSH-mediated SOCS-3 induction was dependent on STAT3. The cell line stably expressing the wild-type STAT3 showed a higher CIITA induction in response to IFN-γ and also exhibited TSH repression of the IFN-γ-mediated induction of CIITA. However, TSH repression of the IFN-γ-induced CIITA expression was not observed in FRTL-5 thyroid cells, which stably expresses the dominant negative forms of STAT3, STAT3-Y705F, and STAT3-S727A. This report suggests that TSH is also engaged in immunomodulation through signal cross-talk with the cytokines in thyroid cells.

Thyroid-stimulating hormone transcriptionally regulates the thiol-specific antioxidant gene.

Thiol-specific antioxidant (TSA) plays an important role in regulating cell differentiation and proliferation by modulating the hydrogen peroxide (H2O2) mediated responses in a variety of mammalian cells. Thyroid cells are constantly exposed to the actions of reactive oxygen species (ROS), because they produce high levels of H2O2 in response to the physiological action of TSH (thyroid-stimulating hormone). Thyrocytes have several defense mechanisms against ROS, including TSA and SOD (superoxide anion dismutase). Using Northern blot hybridization, we tested the effects of TSH on TSA gene expression in FRTL-5 cells derived from rat thyroids. TSA mRNA expression increased following treatment of cells with TSH at concentrations greater than 10-9 M. This effect was observed within 6 hours following treatment, and peaked at 8 hours. The effect was blocked by actinomycin D, but not by cycloheximide. The half-life of TSA mRNA was approximately 5.5 hours in the presence or absence of TSH, and that was not affected by TSA mRNA stability. The effects on TSA gene expression were specific to TSH. Other growth factors (e.g., insulin, transferrin and hydrocortisone) did not alter TSA expression. Our results are the first indication that TSH regulates the expression of TSA transcriptionally in thyrocytes.

Chicken Ovalbumin Upstream Promoter Transcription Factor II Regulates Renin Gene Expression

Background: The production of the hormone renin is transcriptionally regulated. Results: The nuclear receptor COUP-TFII binds to the renin gene promoter and is necessary for the cAMP-induced renin gene expression. Conclusion: COUP-TFII stimulates renin gene transcription. Significance: The molecular mechanisms controlling the expression of renin are crucial for the understanding of its role in blood pressure regulation and nephrogenesis. This study aimed to investigate the possible involvement of the orphan nuclear receptor chicken ovalbumin upstream promoter transcription factor II (COUP-TFII) in the regulation of renin gene expression. COUP-TFII colocalized with renin in the juxtaglomerular cells of the kidney, which are the main source of renin in vivo. Protein-DNA binding studies demonstrated that COUP-TFII binds to an imperfect direct repeat COUP-TFII recognition sequence (termed hereafter proxDR) in the proximal renin promoter. Because cAMP signaling plays a central role in the control of the renin gene expression, we suggested that COUP-TFII may modulate this cAMP effect. Accordingly, knockdown of COUP-TFII in the clonal renin-producing cell lines As4.1 and Calu-6 diminished the stimulation of the renin mRNA expression by cAMP agonists. In addition, the mutation of the proxDR element in renin promoter reporter gene constructs abrogated the inducibility by cAMP. The proxDR sequence was found to be necessary for the function of a proximal renin promoter cAMP-response element (CRE). Knockdown of COUP-TFII or cAMP-binding protein (CREB), which is the archetypal transcription factor binding to CRE, decreased the basal renin gene expression. However, the deficiency of COUP-TFII did not further diminish the renin expression when CREB was knocked down. In agreement with the cell culture studies, mutant mice deficient in COUP-TFII have lower renin expression than their control strain. Altogether our data show that COUP-TFII is involved in the control of renin gene expression.