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From the Division of Molecular Medicine, Harbor-UCLA Medical Center, David Geffen School of Medicine, University of California, Los Angeles, Torrance, California.
PURPOSE. UV-C irradiation of corneal epithelial cells elicits K+ channel activation, which in turn causes them to undergo apoptosis. In the present study, the intermediary role played by mitogen-activated protein kinase (MAPK) signaling pathways in mediating this response was investigated.
METHODS. Western blot and kinase assays were used to measure UV-induced activation (i.e., phosphorylation) of c-Jun NH2-terminal kinase (JNK)/SEK, extracellular signal-regulated kinase (ERK), and p38. Corneal epithelial apoptosis was determined by measuring caspase 3 activity.
RESULTS. UV-irradiation–induced increases in cell membrane K+ channel activity resulted in activations of JNK, SEK upstream of JNK, and caspase 3 downstream of JNK. Suppression of K+ channel activity with specific K+ channel blockers significantly inhibited UV-irradiation–induced activation of JNK cascades. However, suppression of K+ channel activity did not prevent hyperosmotic-stress–induced JNK activation. In addition, UV-irradiation–induced SEK/JNK activation was unaffected by removal of extracellular free Ca2+ with EGTA.
CONCLUSIONS. UV-irradiation–induced corneal epithelial cell apoptosis is mediated through activation of the SEK/JNK signaling pathway. Such activation is dependent on increases in K+ channel activity, which play an important role in the early events that result in activation of this pathway.
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