title: Brain and muscle Arnt-like protein-1 (BMAL1) controls circadian cell proliferation and susceptibility to UVB-induced DNA damage in the epidermis.
abstract: The role of the circadian clock in skin and the identity of genes participating in its chronobiology remain largely unknown, leading us to define the circadian transcriptome of mouse skin at two different stages of the hair cycle, telogen and anagen. The circadian transcriptomes of telogen and anagen skin are largely distinct, with the former dominated by genes involved in cell proliferation and metabolism. The expression of many metabolic genes is antiphasic to cell cycle-related genes, the former peaking during the day and the latter at night. Consistently, accumulation of reactive oxygen species, a byproduct of oxidative phosphorylation, and S-phase are antiphasic to each other in telogen skin. Furthermore, the circadian variation in S-phase is controlled by BMAL1 intrinsic to keratinocytes, because keratinocyte-specific deletion of Bmal1 obliterates time-of-day-dependent synchronicity of cell division in the epidermis leading to a constitutively elevated cell proliferation. In agreement with higher cellular susceptibility to UV-induced DNA damage during S-phase, we found that mice are most sensitive to UVB-induced DNA damage in the epidermis at night. Because in the human epidermis maximum numbers of keratinocytes go through S-phase in the late afternoon, we speculate that in humans the circadian clock imposes regulation of epidermal cell proliferation so that skin is at a particularly vulnerable stage during times of maximum UV exposure, thus contributing to the high incidence of human skin cancers.
authors: Department of Biological Chemistry, University of California, Irvine, CA 92697, USA.
authors: Mikhail
authors: M
authors: Geyfman
authors: Vivek
authors: V
authors: Kumar
authors: Qiang
authors: Q
authors: Liu
authors: Rolando
authors: R
authors: Ruiz
authors: William
authors: W
authors: Gordon
authors: Francisco
authors: F
authors: Espitia
authors: Eric
authors: E
authors: Cam
authors: Sarah E
authors: SE
authors: Millar
authors: Padhraic
authors: P
authors: Smyth
authors: Alexander
authors: A
authors: Ihler
authors: Joseph S
authors: JS
authors: Takahashi
authors: Bogi
authors: B
authors: Andersen
mesh_terms: D056930:ARNTL Transcription Factors / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D001973:Bromodeoxyuridine; D002453:Cell Cycle / Q000502:physiology; D049109:Cell Proliferation; D002940:Circadian Rhythm / Q000235:genetics* / Q000502:physiology; D003078:Colchicine; D004249:DNA Damage / Q000235:genetics* / Q000502:physiology; D004797:Enzyme-Linked Immunosorbent Assay; D000078404:Epidermal Cells; D004817:Epidermis / Q000528:radiation effects; D007150:Immunohistochemistry; D008297:Male; D053858:Metabolic Networks and Pathways / Q000235:genetics* / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL; D046228:Microarray Analysis; D016133:Polymerase Chain Reaction; D059467:Transcriptome / Q000235:genetics* / Q000502:physiology; D014466:Ultraviolet Rays / Q000009:adverse effects
chemical_list: D056930:ARNTL Transcription Factors; C538961:Bmal1 protein, mouse; D001973:Bromodeoxyuridine; D003078:Colchicine