title: Peripheral CLOCK regulates target-tissue glucocorticoid receptor transcriptional activity in a circadian fashion in man.
abstract: OBJECTIVE
  Circulating cortisol fluctuates diurnally under the control of the "master" circadian CLOCK, while the peripheral "slave" counterpart of the latter regulates the transcriptional activity of the glucocorticoid receptor (GR) at local glucocorticoid target tissues through acetylation. In this manuscript, we studied the effect of CLOCK-mediated GR acetylation on the sensitivity of peripheral tissues to glucocorticoids in humans.
  
  
  METHODS
  We examined GR acetylation and mRNA expression of GR, CLOCK-related and glucocorticoid-responsive genes in peripheral blood mononuclear cells (PBMCs) obtained at 8 am and 8 pm from 10 healthy subjects, as well as in PBMCs obtained in the morning and cultured for 24 hours with exposure to 3-hour hydrocortisone pulses every 6 hours. We used EBV-transformed lymphocytes (EBVLs) as non-synchronized controls.
  
  
  RESULTS
  GR acetylation was higher in the morning than in the evening in PBMCs, mirroring the fluctuations of circulating cortisol in reverse phase. All known glucocorticoid-responsive genes tested responded as expected to hydrocortisone in non-synchronized EBVLs, however, some of these genes did not show the expected diurnal mRNA fluctuations in PBMCs in vivo. Instead, their mRNA oscillated in a Clock- and a GR acetylation-dependent fashion in naturally synchronized PBMCs cultured ex vivo in the absence of the endogenous glucocorticoid, suggesting that circulating cortisol might prevent circadian GR acetylation-dependent effects in some glucocorticoid-responsive genes in vivo.
  
  
  CONCLUSIONS
  Peripheral CLOCK-mediated circadian acetylation of the human GR may function as a target-tissue, gene-specific counter regulatory mechanism to the actions of diurnally fluctuating cortisol, effectively decreasing tissue sensitivity to glucocorticoids in the morning and increasing it at night.
authors: First Department of Pediatrics, University of Athens Medical School, "Aghia Sophia" Children's Hospital, Athens, Greece.
authors: Evangelia
authors: E
authors: Charmandari
authors: George P
authors: GP
authors: Chrousos
authors: George I
authors: GI
authors: Lambrou
authors: Aikaterini
authors: A
authors: Pavlaki
authors: Hisashi
authors: H
authors: Koide
authors: Sinnie Sin Man
authors: SS
authors: Ng
authors: Tomoshige
authors: T
authors: Kino
mesh_terms: D000107:Acetylation; D000324:Adrenocorticotropic Hormone / Q000097:blood; D000328:Adult; D056926:CLOCK Proteins / Q000378:metabolism*; D002940:Circadian Rhythm / Q000235:genetics*; D005260:Female; D005786:Gene Expression Regulation / Q000235:genetics*; D006801:Humans; D006854:Hydrocortisone / Q000097:blood; D007030:Hypothalamo-Hypophyseal System / Q000378:metabolism / Q000502:physiology; D007963:Leukocytes, Mononuclear / Q000378:metabolism; D008297:Male; D010913:Pituitary-Adrenal System / Q000378:metabolism / Q000502:physiology; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011965:Receptors, Glucocorticoid / Q000235:genetics* / Q000378:metabolism; D013312:Stress, Physiological / Q000235:genetics / Q000502:physiology; D014158:Transcription, Genetic / Q000235:genetics*
chemical_list: D012333:RNA, Messenger; D011965:Receptors, Glucocorticoid; D000324:Adrenocorticotropic Hormone; D056926:CLOCK Proteins; D006854:Hydrocortisone