title: Shikonin shortens the circadian period: possible involvement of Top2 inhibition.
abstract: The naphthoquinone pigment, shikonin, is a natural product derived from Lithospermum erythrorhizon and an active component of a Chinese traditional herbal therapeutic. We identified shikonin as a candidate for shortening the circadian period using real-time reporter gene assays based on NIH3T3-derived stable reporter cells. Period length that became shortened in cells incubated with shikonin or etoposide reverted to that of control cells after continued incubation without these compounds. These findings indicated that shikonin and etoposide shorten the circadian period reversibly and through similar mechanisms. Topoisomerase II (Top2)-specific decatenation assays confirmed that shikonin, liker etoposide, is a Top2 inhibitor. Shikonin was incorporated into the nucleus and Top2 was located in the Bmal1 promoter, suggesting the relationship between Bmal1 transcription and Top2 inhibition. Top2a siRNA also shortened period length, suggesting that Top2 is involved in this process. Promoter assays showed that Top2a siRNA, etoposide and shikonin reduce Bmal1 promoter activity. These findings indicated that Top2 is involved in Bmal1 transcription and influences the circadian period, and that shikonin is a novel contributor to the control of period length in mammalian cells.
authors: Biomedical Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Higashi 1-1-1, Tsukuba 305-8566, Japan.
authors: Yoshikatsu
authors: Y
authors: Ogawa
authors: Biomedical Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Higashi 1-1-1, Tsukuba 305-8566, Japan.
authors: Yasuhiro
authors: Y
authors: Kawano
authors: Biomedical Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Higashi 1-1-1, Tsukuba 305-8566, Japan.
authors: Yoshimitsu
authors: Y
authors: Yamazaki
authors: Biomedical Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Higashi 1-1-1, Tsukuba 305-8566, Japan. Electronic address: y-onishi@aist.go.jp.
authors: Yoshiaki
authors: Y
authors: Onishi
mesh_terms: D056930:ARNTL Transcription Factors / Q000378:metabolism*; D000818:Animals; D000951:Antigens, Neoplasm / Q000235:genetics; D002940:Circadian Rhythm / Q000187:drug effects*; D004250:DNA Topoisomerases, Type II / Q000235:genetics; D004268:DNA-Binding Proteins / Q000037:antagonists & inhibitors* / Q000235:genetics; D004365:Drugs, Chinese Herbal / Q000494:pharmacology*; D055785:Gene Knockdown Techniques; D051379:Mice; D041681:NIH 3T3 Cells; D009285:Naphthoquinones / Q000494:pharmacology*; D000075223:Poly-ADP-Ribose Binding Proteins; D014158:Transcription, Genetic
chemical_list: D056930:ARNTL Transcription Factors; D000951:Antigens, Neoplasm; C538961:Bmal1 protein, mouse; D004268:DNA-Binding Proteins; D004365:Drugs, Chinese Herbal; D009285:Naphthoquinones; D000075223:Poly-ADP-Ribose Binding Proteins; C016101:shikonin; D004250:DNA Topoisomerases, Type II; C000618812:Top2a protein, mouse
keywords: Circadian rhythm; Clock genes; Topoisomerase; Transcription