title: ATR-Chk1 pathway inhibition promotes apoptosis after UV treatment in primary human keratinocytes: potential basis for the UV protective effects of caffeine.
abstract: New approaches to prevent and reverse UV damage are needed to combat rising sunlight-induced skin cancer rates. Mouse studies have shown that oral or topical caffeine promotes elimination of UV-damaged keratinocytes through apoptosis and markedly inhibits subsequent skin cancer development. This potentially important therapeutic effect has not been studied in human skin cells. Here, we use primary human keratinocytes to examine which of several caffeine effects mediates this process. In these cells, caffeine more than doubled apoptosis after 75 mJ cm(-2) of ultraviolet light B (UVB). Selectively targeting two of caffeine's known effects did not alter UVB-induced apoptosis: inhibition of ataxia-telangiectasia mutated and augmentation of cyclic AMP levels. In contrast, siRNA against ataxia-telangiectasia and Rad3-related (ATR) doubled apoptosis after UV through a p53-independent mechanism. Caffeine did not further augment apoptosis after UVB in cells in which ATR had been specifically depleted, suggesting that a key target of caffeine in this effect is ATR. Inhibition of a central ATR target, checkpoint kinase 1 (Chk1), through siRNA or a new and highly specific inhibitor (PF610666) also augmented UVB-induced apoptosis. These data suggest that a relevant target of caffeine is the ATR-Chk1 pathway and that inhibiting ATR or Chk1 might have promise in preventing or reversing UV damage.
authors.affiliation: Cutaneous Biology Research Center, Massachusetts General Hospital, Harvard Medical School, Charlestown, Massachusetts, USA.
authors.forename: Timothy P
authors.initials: TP
authors.lastname: Heffernan
authors.forename: Masaoki
authors.initials: M
authors.lastname: Kawasumi
authors.forename: Alessandra
authors.initials: A
authors.lastname: Blasina
authors.forename: Kenna
authors.initials: K
authors.lastname: Anderes
authors.forename: Allan H
authors.initials: AH
authors.lastname: Conney
authors.forename: Paul
authors.initials: P
authors.lastname: Nghiem
mesh_terms: D000328:Adult; D000368:Aged; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D064007:Ataxia Telangiectasia Mutated Proteins; D002110:Caffeine / Q000494:pharmacology*; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism*; D002478:Cells, Cultured; D000071877:Checkpoint Kinase 1; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D000078404:Epidermal Cells; D005260:Female; D006801:Humans; D015603:Keratinocytes / Q000166:cytology / Q000378:metabolism* / Q000528:radiation effects*; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects / Q000528:radiation effects; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D034741:RNA, Small Interfering; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism; D014466:Ultraviolet Rays / Q000009:adverse effects*
chemical_list: D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D010726:Phosphodiesterase Inhibitors; D034741:RNA, Small Interfering; D016159:Tumor Suppressor Protein p53; D025521:Tumor Suppressor Proteins; D002110:Caffeine; D011494:Protein Kinases; C576324:ATM protein, human; C576597:ATR protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; C576325:Atm protein, mouse; C000605867:CHEK1 protein, human; D000071877:Checkpoint Kinase 1; C000605869:Chek1 protein, mouse; D017346:Protein Serine-Threonine Kinases