title: Evidence for circadian regulation of activating transcription factor 5 but not tyrosine hydroxylase by the chromaffin cell clock.
abstract: In mammals, adrenal medulla chromaffin cells constitute a fundamental component of the sympathetic nervous system outflow, producing most of the circulating adrenaline. We recently found that the rhesus monkey adrenal gland expresses several genes in a 24-h rhythmic pattern, including TH (the rate-limiting enzyme in catecholamine synthesis) and Atf5 (a transcription factor involved in apoptosis and neural cell differentiation) together with the core-clock genes. To examine whether these core-clock genes play a role in adrenal circadian function, we exposed rat pheochromocytoma PC12 cells to a serum shock and found that it triggered rhythmic oscillation of the clock genes rBmal1, rPer1, rRev-erbalpha, and rCry1 and induced the circadian expression of Atf5 but not TH. Furthermore, we found that the CLOCK/brain and muscle Arnt-like protein-1 (BMAL1) heterodimer could regulate Atf5 expression by binding to an E-box motif and repressing activity of its promoter. The physiological relevance of this interaction was evident in Bmal1 -/- mice, in which blunted circadian rhythm of Atf5 mRNA was observed in the liver, together with significantly higher expression levels in both liver and adrenal glands. Although we found no compelling evidence for rhythmic expression of TH in chromaffin cells being regulated by an intrinsic molecular clock mechanism, the Atf5 results raise the possibility that other aspects of chromaffin cell physiology, such as cell survival and cell differentiation, may well be intrinsically regulated.
authors.affiliation: Division of Neuroscience, Oregon National Primate Research Center, 505 Northwest 185th Avenue, Beaverton, OR 97006, USA.
authors.forename: Dario R
authors.initials: DR
authors.lastname: Lemos
authors.forename: Leela
authors.initials: L
authors.lastname: Goodspeed
authors.forename: Luciana
authors.initials: L
authors.lastname: Tonelli
authors.forename: Marina P
authors.initials: MP
authors.lastname: Antoch
authors.forename: Sergio R
authors.initials: SR
authors.lastname: Ojeda
authors.forename: Henryk F
authors.initials: HF
authors.lastname: Urbanski
mesh_terms: D056930:ARNTL Transcription Factors; D051696:Activating Transcription Factors / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics / Q000378:metabolism; D056926:CLOCK Proteins; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism; D019439:Chromaffin Cells / Q000378:metabolism*; D002940:Circadian Rhythm; D056931:Cryptochromes; D016895:Culture Media, Serum-Free / Q000494:pharmacology; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D024202:Electrophoretic Mobility Shift Assay; D005260:Female; D005420:Flavoproteins / Q000235:genetics / Q000378:metabolism; D015870:Gene Expression / Q000187:drug effects; D007150:Immunohistochemistry; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D016297:Mutagenesis, Site-Directed; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D056953:Nuclear Receptor Subfamily 1, Group D, Member 1; D016716:PC12 Cells; D056950:Period Circadian Proteins; D011485:Protein Binding; D051381:Rats; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism; D014446:Tyrosine 3-Monooxygenase / Q000235:genetics / Q000378:metabolism*