The circadian clock component BMAL1 is a critical regulator of p21WAF1/CIP1 expression and hepatocyte proliferation.
Most living organisms show circadian (approximately 24 h) rhythms in physiology and behavior. These oscillations are generated by endogenous circadian clocks, present in virtually all cells where they control key biological processes. Although circadian gating of mitosis has been reported for many years in some peripheral tissues, the underlying molecular mechanisms have remained poorly understood. Here we show that the cell cycle inhibitor p21WAF1/CIP1 is rhythmically expressed in mouse peripheral organs. This rhythmic pattern of mRNA and protein expression was recapitulated in vitro in serum-shocked differentiated skeletal muscle cells. p21WAF1/CIP1 circadian expression is dramatically increased and no longer rhythmic in clock-deficient Bmal1-/- knock-out mice. Biochemical and genetic data show that oscillation of p21WAF1/CIP1 gene transcription is regulated by the antagonistic activities of the orphan nuclear receptors REV-ERBalpha/beta and RORalpha4/gamma, which are core clock regulators. Importantly, p21WAF1/CIP1 overexpressing Bmal1-/- primary hepatocytes exhibit a decreased proliferation rate. This phenotype could be reversed using small interfering RNA-mediated knockdown of p21WAF1/CIP1. These data establish a novel molecular link between clock and cell cycle genes and suggest that the G1 progression phase is a target of the circadian clock during liver cell proliferation.
Gréchez-Cassiau
Aline
A
Laboratoire de Biologie et Physiopathologie des Systèmes Intégrés, Université de Nice-Sophia-Antipolis, Centre National de la Recherche Scientifique, 06108 Nice cedex 2, France.
Rayet
Béatrice
B
Guillaumond
Fabienne
F
Teboul
Michèle
M
Delaunay
Franck
F
D056930:ARNTL Transcription Factors; D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics / Q000378:metabolism*; D002940:Circadian Rhythm / Q000502:physiology*; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000037:antagonists & inhibitors / Q000096:biosynthesis* / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D016193:G1 Phase / Q000502:physiology*; D005786:Gene Expression Regulation / Q000502:physiology*; D022781:Hepatocytes / Q000166:cytology / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D008938:Mitosis / Q000235:genetics*; D018485:Muscle Fibers, Skeletal / Q000166:cytology / Q000378:metabolism; D041681:NIH 3T3 Cells; D056953:Nuclear Receptor Subfamily 1, Group D, Member 1; D057094:Nuclear Receptor Subfamily 1, Group F, Member 1; D057132:Nuclear Receptor Subfamily 1, Group F, Member 3; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D034741:RNA, Small Interfering / Q000235:genetics; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics / Q000378:metabolism; D018168:Receptors, Retinoic Acid / Q000235:genetics / Q000378:metabolism; D011988:Receptors, Thyroid Hormone / Q000235:genetics / Q000378:metabolism; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic / Q000502:physiology
D056930:ARNTL Transcription Factors; D051792:Basic Helix-Loop-Helix Proteins; D050759:Cyclin-Dependent Kinase Inhibitor p21; D004268:DNA-Binding Proteins; D056953:Nuclear Receptor Subfamily 1, Group D, Member 1; D057094:Nuclear Receptor Subfamily 1, Group F, Member 1; D057132:Nuclear Receptor Subfamily 1, Group F, Member 3; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D018160:Receptors, Cytoplasmic and Nuclear; D018168:Receptors, Retinoic Acid; D011988:Receptors, Thyroid Hormone; D012097:Repressor Proteins; D015534:Trans-Activators; D014157:Transcription Factors; C538960:BMAL1 protein, human; C538961:Bmal1 protein, mouse; C493957:Cdkn1a protein, mouse; C090977:NR1D2 protein, human; C498262:Nr1d1 protein, mouse; C539900:RORC protein, human; C539901:Rorc protein, mouse