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      NGFI-B (Nurr77/Nr4a1) orphan nuclear receptor in rat pinealocytes: circadian expression involves an adrenergic-cyclic AMP mechanism.

      Journal of Neurochemistry
      Animals, Animals, Genetically Modified, Bucladesine, pharmacology, Cell Nucleus, metabolism, Circadian Rhythm, physiology, Cyclic AMP, DNA-Binding Proteins, genetics, Electrophoretic Mobility Shift Assay, Fos-Related Antigen-2, Gene Expression Regulation, Genes, Dominant, Male, Norepinephrine, Nuclear Receptor Subfamily 4, Group A, Member 1, Organ Culture Techniques, Pineal Gland, chemistry, drug effects, RNA, Messenger, Rats, Rats, Sprague-Dawley, Receptors, Adrenergic, Receptors, Cytoplasmic and Nuclear, Receptors, Steroid, Response Elements, Transcription Factors

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          Abstract

          NGFI-B (Nur77/Nr4a1) is a member of a nuclear steroid receptor subgroup that includes the related factors Nurr1 (Nr4a2) and NOR-1 (Nr4a3). These proteins do not have recognized ligands and in fact function independently as orphan receptors with transcriptional regulatory activity. In the present study, expression of the NGFI-B gene in the rat pineal gland was found to exhibit a robust circadian rhythm, with elevated levels of NGFI-B mRNA occurring at night. The rhythm of NGFI-B mRNA is translated into a circadian rhythm of NGFI-B protein, which accumulates in the nucleus of pinealocytes. In addition, there is a parallel marked nocturnal increase in pineal DNA binding activity to a NGFI-B response element (NBRE, AAAGGTCA). Pharmacological studies indicate that NGFI-B mRNA and protein levels are elevated via activation of adrenergic receptors. NGFI-B protein levels are also elevated by dibutyryl cyclic AMP, as in other systems. In the pineal gland, regulation of NGFI-B expression also involves the AP-1 protein Fra-2, based on studies with a transgenic Fra-2 knockdown rat, in which pineal NGFI-B expression increases. This set of observations extends the number of pineal genes that are known to be regulated by Fra-2, and also provides the first indication that a member of the NGFI-B group of nuclear receptors is involved in controlling gene expression in the pineal gland.

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