title: Clock regulation of dietary lipid absorption.
abstract: OBJECTIVE
  To summarize the new knowledge about the regulation of dietary lipid absorption by circadian locomotor output cycles kaput (Clock) and Nocturnin.
  
  
  RESULTS
  Recent findings have shown that Clock and Nocturnin, proteins involved in circadian regulation, play an important role in the regulation of dietary lipid absorption. Clock deficiency increases, whereas Nocturnin deficiency decreases lipid absorption. Clock plays a role in turning off the genes involved in lipid absorption at the onset of the day. Molecular studies revealed that Clock binds to the promoter of small heterodimer partner to enhance its transcription. When levels are high, small heterodimer partner interacts with the transcription factors associated with the promoter of microsomal triglyceride transfer protein to repress transcription. Reduced microsomal triglyceride transfer protein levels are correlated with low intestinal lipid absorption and plasma lipid levels. In contrast, Nocturnin assists in lipid absorption by regulating their partitioning in different intracellular compartments.
  
  
  CONCLUSIONS
  Clock and Nocturnin regulate lipid absorption involving different mechanisms. It is likely that other clock genes also modulate lipid absorption and plasma lipid levels.
authors.affiliation: Departments of Cell Biology and Pediatrics, SUNY Downstate Medical Center, Brooklyn, New York, USA. Mahmood.hussain@downstate.edu
authors.forename: M Mahmood
authors.initials: MM
authors.lastname: Hussain
authors.forename: Xiaoyue
authors.initials: X
authors.lastname: Pan
mesh_terms: D000818:Animals; D056926:CLOCK Proteins / Q000235:genetics / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism; D057906:Circadian Clocks / Q000235:genetics*; D004041:Dietary Fats / Q000378:metabolism*; D005786:Gene Expression Regulation; D006801:Humans; D007408:Intestinal Absorption / Q000235:genetics; D050356:Lipid Metabolism / Q000235:genetics; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic
chemical_list: D002352:Carrier Proteins; D004041:Dietary Fats; D009687:Nuclear Proteins; D018160:Receptors, Cytoplasmic and Nuclear; D014157:Transcription Factors; C106092:microsomal triglyceride transfer protein; C102804:nocturnin; C099713:nuclear receptor subfamily 0, group B, member 2; D056926:CLOCK Proteins