Karolinska Institutet
Browse

File(s) not publicly available

Functional studies on the orphan receptor Nurr1 and related retinoid receptors

thesis
posted on 2024-09-02, 17:02 authored by Diogo Sampaio e Castro

Nuclear receptors (NRs) constitute a large family of ligand-inducible transcription factors which includes receptors for steroid hormones, retinoids (vitamin A derivatives), vitamin D an d thyroid hormone. The family also includes a large number of structurally related proteins that lack identified ligands and are therefore refered to as orphan receptors. Retinoid signaling is mediated by the retinoic acid receptors (RARs) and retinoid X receptors (RXRs), with RAR/RXR being the main functional units. It has been shown that RAR can be activated in RAR/RXR heterodimers, whereas RXR is believed to be a silent partner.

Our studies on the retinoid receptors demonstrated that the inhibition of RXR is not obligatory and that RXR can be activated in the RAR/RXR heterodimer, in the presence of RAR ligands. These results provide a base for the synergism observed between RAR and RXR activation in processes such as cell differentiation. Nurr1 is an orphan nuclear receptor expressed in the central nervous system, which plays a critical role in the development of midbrain dopaminergic neurons, the cells that degenerate in Parkinson's disease. The mechanisms whereby Nurr1 mediates this process are not understood.

The ligand-binding domain (LBD) of NRs encompasses a ligand dependent activation function (called A172) which, upon ligand binding, is essential for recruitment of transcription mediator proteins called coactivators. Our functional studies on the orphan receptor Nurr1 revealed that Nurr1 LBD has an intrinsic capacity to activate transcription in a cell type dependent fashion, in the absence of exogenously added ligands. The unusual structural features of Nurr1 AF2 suggest an alternative mechanism for coactivator recruitment by this orphan receptor. This was supported by our observation that Nurr1 did not appear to be stimulated by several previously identified NR coactivators. Importantly, our results demonstrated an important role for the Nurr1 AF2 region in transactivation, consistent with the possibility of finding ligands that could regulate Nurr1 activity.

We investigated the role of Nuff I in dopaminergic cell differentiation using the MN9D cell line as a model. Nurr1 expression in MN9D cells induced morphological differentiation associated with neurite outgrowth and growth arrest at GI phase of cell cycle. By using different Nurr1 derivatives, we were able to characterize the functional requirements for Nuff I mediating this process, thus generating important insights into the Nurr1 function in vivo. Overall, our results suggest a dual regulatory role for Nurr1 in the control of cell proliferation and dopaminergic differentiation in the CNS.

The potential of using Nurr1 for inducing a dopaminergic phenotype in neural stem cells was explored by stably transfecting Nurr1 in the neural stem cell line C 17.2. Cells from C 17.2-Nurr I clones could be induced to become dopaminergic when differentiated in the presence of type l astrocytes from the ventral midbrain. Importantly, our results suggest an instructive role for astrocytes in the process of neuronal differentiation in vivo. In addition, they demonstrate the potential for manipulating gene expression in neural stem cells, aimed at generating an unlimited number of neurons of a desired phenotype for cell replacement strategies in the context of neurodegenerative diseases.

List of scientific papers

I. Botling J, Castro DS, Öberg F, Nilsson K, Perlmann T (1997). "Retinoic acid receptor/retinoid X receptor heterodimers can be activated through both subunits providing a basis for synergistic transactivation and cellular differentiation" J Biol Chem 272(14): 9443-9
https://pubmed.ncbi.nlm.nih.gov/9083083

II. Castro DS, Arvidsson M, Bondesson Bolin M, Perlmann T (1999). "Activity of the Nurr1 carboxyl-terminal domain depends on cell type and integrity of the activation function 2" J Biol Chem 274(52): 37483-90
https://pubmed.ncbi.nlm.nih.gov/10601324

III. Castro DS, Joseph B, Hermanson E, Aarnisalo P, Walén Å, Hengerer B, Perlmann T (2001). "Induction of G1 arrest and morphological differentiation by Nurr1 expression in dopamine MN9D cells" (Manuscript)

IV. Wagner J, Åkerud P, Castro DS, Holm PC, Canals JM, Snyder EY, Perlmann T, Arenas E (1999). "Induction of a midbrain dopaminergic phenotype in Nurr1-overexpressing neural stem cells by type 1 astrocytes" Nat Biotechnol 17(7): 653-9
https://pubmed.ncbi.nlm.nih.gov/10404157

History

Defence date

2001-01-26

Department

  • Department of Cell and Molecular Biology

Publication year

2001

Thesis type

  • Doctoral thesis

ISBN-10

91-628-4608-6

Number of supporting papers

4

Language

  • eng

Original publication date

2001-01-05

Author name in thesis

Castro, Diogo Sampaio e

Original department name

Department of Cell and Molecular Biology

Place of publication

Stockholm

Usage metrics

    Theses

    Categories

    No categories selected

    Keywords

    Exports

    RefWorks
    BibTeX
    Ref. manager
    Endnote
    DataCite
    NLM
    DC