Pathway-specific effect of caffeine on protection against UV irradiation-induced apoptosis in corneal epithelial cells.
OBJECTIVE
To define the role of molecular interaction between the UV-induced JNK (c-Jun N-terminal kinase) cascade and corneal epithelial cell apoptosis and protection against apoptosis by caffeine.


METHODS
Rabbit and human corneal epithelial cells were cultured in DMEM/F12 medium containing 10% FBS and 5 microg/mL insulin at 37 degrees C in 5% CO(2). DNA fragmentation and ethidium bromide/acridine orange (EB/AO) nuclear staining were performed to detect cell death. Western blot, immunoprecipitation, and kinase assays were used to measure UV-induced mitogen-activated protein (MAP) kinase activity.


RESULTS
UV irradiation-induced apoptosis through apoptosis signal-regulating kinase 1 (ASK1) and MAKK4 (SEK1) upstream from JNK was caffeine sensitive. Caffeine (1,3,7-trimethylxanthine), an agent that is one of the most popular additions to food consumed in the world and a potential enhancer of chemotherapy, effectively protected corneal epithelial cells against apoptosis by its specific effect on the JNK cascade. Theophylline (1,3-dimethylxanthine) exhibited an effect similar to that of caffeine on prevention of UV irradiation-induced apoptosis. However, alterations of either intracellular cAMP or Ca(2+) levels did not alter the effect of caffeine on the JNK signaling pathway. In addition, the blockade of PI3K-like kinases by wortmannin had no impact on the protective effect of caffeine against UV irradiation-induced apoptosis, suggesting that the protective effect of caffeine acts through a specific mechanism involving UV irradiation-induced activation of ASK1 and SEK1. In contrast, caffeine had no effects on melphalan-, hyperosmotic stress-, or IL-1beta-induced activation of the JNK signaling pathway in these cells.


CONCLUSIONS
UV irradiation stress-induced activation of the ASK1-SEK1-JNK signaling pathway leading to apoptosis is a caffeine-sensitive process, and caffeine, as a multifunctional agent in cells, can specifically interact with the pathway to protect against apoptosis.
Wang
Ling
L
Department of Medicine, HMC, David Geffen School of Medicine, University of California Los Angeles, Torrance, California 90502, USA.
Lu
Luo
L
D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D017209:Apoptosis / Q000528:radiation effects*; D015153:Blotting, Western; D002110:Caffeine / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D000242:Cyclic AMP / Q000378:metabolism; D053938:DNA Fragmentation; D019573:Epithelium, Corneal / Q000187:drug effects* / Q000473:pathology / Q000528:radiation effects; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism*; D048670:MAP Kinase Kinase 4 / Q000378:metabolism; D048848:MAP Kinase Kinase Kinase 5 / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology*; D010766:Phosphorylation; D011817:Rabbits; D013806:Theophylline / Q000494:pharmacology; D014466:Ultraviolet Rays; D000077191:Wortmannin; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
D000730:Androstadienes; D010726:Phosphodiesterase Inhibitors; D002110:Caffeine; D013806:Theophylline; D000242:Cyclic AMP; D019869:Phosphatidylinositol 3-Kinases; D048049:Extracellular Signal-Regulated MAP Kinases; D048031:JNK Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D048848:MAP Kinase Kinase Kinase 5; C482858:MAP3K5 protein, human; D048670:MAP Kinase Kinase 4; D002118:Calcium; D000077191:Wortmannin