A canonical nerve growth factor-induced gene-B response element appears not to be involved in the cyclic adenosine monophosphate-dependent expression of differentiation in thyrocytes

TR3 orphan receptor is expressed in vascular endothelial cells and mediates cell cycle arrest

OBJECTIVE

Endothelial cells play a pivotal role in vascular homeostasis. In this study, we investigated the function of the nerve growth factor-induced protein-B (NGFI-B) subfamily of nuclear receptors comprising the TR3 orphan receptor (TR3), mitogen-induced nuclear orphan receptor (MINOR), and nuclear orphan receptor of T cells (NOT) in endothelial cells.

METHODS AND RESULTS

The mRNA expression of TR3, MINOR, and NOT in atherosclerotic lesions was assessed in human vascular specimens. Each of these factors is expressed in smooth muscle cells, as described before, and in subsets of endothelial cells, implicating that they might affect endothelial cell function. Adenoviral overexpression of TR3 in cultured endothelial cells resulted in decreased [3H]thymidine incorporation, whereas a dominant-negative TR3 variant that inhibits the activity of endogenous TR3-like factors enhanced DNA synthesis. TR3 interfered with progression of the cell cycle by upregulating p27Kip1 and downregulating cyclin A, whereas expression levels of a number of other cell cycle-associated proteins remained unchanged.

CONCLUSIONS

These findings demonstrate that TR3 is a modulator of endothelial cell proliferation and arrests endothelial cells in the G1 phase of the cell cycle by influencing cell cycle protein levels. We hypothesize involvement of TR3 in the maintenance of integrity of the vascular endothelium.

Dimer-specific potentiation of NGFI-B (Nur77) transcriptional activity by the protein kinase A pathway and AF-1-dependent coactivator recruitment

The NGFI-B (Nur77) subfamily of orphan nuclear receptors (NRs), which also includes Nurr1 and NOR1, bind the NurRE regulatory element as either homo- or heterodimers formed between subfamily members. These NRs mediate the activation of pituitary proopiomelanocortin (POMC) gene transcription by the hypothalamic hormone corticotropin-releasing hormone (CRH), an important link between neuronal and endocrine components of the hypothalamo-pituitary-adrenal axis. CRH effects on POMC transcription do not require de novo protein synthesis. We now show that CRH signals activate Nur factors through the cyclic AMP/protein kinase A (PKA) pathway. CRH and PKA rapidly increase nuclear DNA binding activity of NGFI-B dimers but not monomers. Accordingly, CRH- or PKA-activated Nur factors enhance dimer (but not monomer) target response elements. We also show that p160/SRC coactivators are recruited to Nur dimers (but not to monomers) and that coactivator recruitment to the NurRE is enhanced in response to CRH. Moreover, PKA- and coactivator-induced potentiation of NGFI-B activity are primarily exerted through the N-terminal AF-1 domain of NGFI-B. The TIF2 (SRC-2) glutamine-rich domain is required for this activity. Taken together, these results indicate that Nur factors behave as endpoint effectors of the PKA signaling pathway acting through dimers and AF-1-dependent recruitment of coactivators.

Protective function of transcription factor TR3 orphan receptor in atherogenesis: decreased lesion formation in carotid artery ligation model in TR3 transgenic mice

BACKGROUND

Smooth muscle cells (SMCs) play a key role in intimal thickening in atherosclerosis and restenosis. The precise signaling pathways by which the proliferation of SMCs is regulated are largely unknown. The TR3 orphan receptor, the mitogen-induced nuclear orphan receptor (MINOR), and the nuclear receptor of T cells (NOT) are a subfamily of transcription factors belonging to the nuclear receptor superfamily and are induced in activated SMCs. In this study, we investigated the role of these transcription factors in SMC proliferation in atherogenesis.

METHODS AND RESULTS

Multiple human vascular specimens at distinct stages of atherosclerosis (lesion types II to V by American Heart Association classification) derived from 14 different individuals were studied for expression of these transcription factors. We observed expression of TR3, MINOR, and NOT in neointimal SMCs, whereas no expression was detected in medial SMCs. Adenovirus-mediated expression of a dominant-negative variant of TR3, which suppresses the transcriptional activity of each subfamily member, increases DNA synthesis and decreases p27(Kip1) protein expression in cultured SMCs. We generated transgenic mice that express this dominant-negative variant or full-length TR3 under control of a vascular SMC-specific promoter. Carotid artery ligation of transgenic mice that express the dominant-negative variant of TR3 in arterial SMCs, compared with lesions formed in wild-type mice, results in a 3-fold increase in neointimal formation, whereas neointimal formation is inhibited 5-fold in transgenic mice expressing full-length TR3.

CONCLUSIONS

Our results reveal that TR3 and possibly other members of this transcription factor subfamily inhibit vascular lesion formation. These transcription factors could serve as novel targets in the treatment of vascular disease.

Nerve growth factor and retinoic acid inhibit proliferation and invasion in thyroid tumor cells

NGF has anti-proliferative and anti-invasive effects in neuroendocrine tumors. In the present work we examined the effects of NGF and retinoic acid on cell proliferation and invasion in thyroid carcinoma cells. We found that NGF and retinoic acid do not affect cell proliferation on their own but in combination they produce a strong inhibition. We also found that retinoic acid regulates the matrix metalloproteinase 2 activity and invasion. In contrast, NGF inhibited invasion and reverted the effect of retinoic acid. This effect of NGF is likely mediated by an increase in adhesion to laminin and collagen IV and the inhibition of cell migration. NGF also induced the expression of the p75 NGF receptor. In conclusion, NGF and retinoic acid in combination inhibit proliferation and invasion of thyroid papillary carcinoma cells. These data open the possibility of a potential combined therapy for thyroid papillary carcinomas.