A divergent role of COOH-terminal domains in Nurr1 and Nur77 transactivation

• Published in: Gene expression 1998-01, Vol.7 (1), p.1-12
• Main Authors: Castillo, S O, Xiao, Q, Kostrouch, Z, Dozin, B, Nikodem, V M
• Format: Article
• Language: English
• Subjects: 3T3 Cells; Alternative Splicing; Amino Acid Sequence; Animals; Base Sequence; Binding Sites; Chromosome Mapping; Cloning, Molecular; DNA - metabolism; DNA-Binding Proteins - chemistry; DNA-Binding Proteins - genetics; DNA-Binding Proteins - metabolism; Mice; Molecular Sequence Data; Nerve Tissue Proteins - genetics; Nerve Tissue Proteins - metabolism; Nuclear Proteins - metabolism; Nuclear Receptor Subfamily 4, Group A, Member 1; Nuclear Receptor Subfamily 4, Group A, Member 2; Receptors, Cytoplasmic and Nuclear; Receptors, Retinoic Acid - metabolism; Receptors, Steroid - chemistry; Receptors, Steroid - genetics; Receptors, Steroid - metabolism; Retinoid X Receptors; Structure-Activity Relationship; Transcription Factors - chemistry; Transcription Factors - genetics; Transcription Factors - metabolism; Transcriptional Activation; Tretinoin - metabolism
• ISSN: 1052-2166; 1555-3884

Orphan nuclear receptors such as Nurr1 and Nur77 have conserved amino acid sequences in the zinc finger DNA binding domains and similar COOH-terminal regions, but have no known ligands. These receptors can bind DNA sequences (response elements) as monomers and can also heterodimerize with the retinoid X receptor to activate transcription. We report here the identification and initial characterization of a novel COOH-terminal truncated isoform of Nurr1, Nurr1a. Internal splicing of Nurr1 generates a frameshift such that a stop codon is prematurely encoded resulting in a naturally occurring COOH-terminal truncation. Embryonic and postnatal mouse brain showed both Nurr1 and Nurr1a mRNAs expressed during development. To characterize essential COOH-terminal elements that may be deleted from Nurr1a and determine function in putative ligand binding, we created COOH-terminal deletion mutants. Nurr1, Nur77, and 3'-truncated mutants bind in gel mobility shift assays to the monomeric Nur77 response element (B1A-RE). However, in transient transfection assays, a truncation of as little as 15 Nurr1 COOH-terminal amino acids diminished transcriptional activation of B1A-thymidine kinase-chloramphenicol acetyltransferase reporter. This result was not seen for a similar Nur77 deletion mutant, Nur77-586. Unlike full-length Nurr1 and Nur77, transactivation by Nur77-586 was not augmented in response to the presence of retinoid-like receptor and 9-cis-retinoic acid. Thus, the interaction of putative ligand binding and transactivation for Nurr1 and Nur77 may function differently.