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UV-induced signaling pathways associated with corneal epithelial cell apoptosis
Luo Lu1, Ling Wang, Beth Shell
1Division of Molecular Medicine, Harbor-UCLA Medical Center, UCLA School of Medicine, University of California-Los Angeles, 1124 W. Carson Street, Torrance, CA 90502, USA. lluou@ucla.edu
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 NH(2)-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.
Insights
UV-C irradiation triggers corneal cell death via potassium (K+) channel activation and subsequent mitogen-activated protein kinase (MAPK) pathway signaling. This pathway, specifically SEK/JNK, is crucial for UV-induced apoptosis in corneal epithelial cells.
Area of Science:
- Ocular surface science
- Cellular signaling
- Apoptosis research
Background:
- Ultraviolet-C (UV-C) irradiation induces apoptosis in corneal epithelial cells.
- Potassium (K+) channel activation is a known response to UV-C irradiation in these cells.
Purpose of the Study:
- To investigate the role of mitogen-activated protein kinase (MAPK) signaling pathways in UV-C-induced corneal epithelial cell apoptosis.
- To elucidate the intermediary mechanisms linking K+ channel activation to apoptosis.
Main Methods:
- Western blot and kinase assays to measure MAPK pathway activation (JNK/SEK, ERK, p38).
- Measurement of caspase 3 activity to quantify apoptosis.
- Utilized K+ channel blockers and EGTA to assess pathway dependency.
Main Results:
- UV-C irradiation activated SEK/JNK and caspase 3, with K+ channel activity increases preceding these events.
- K+ channel blockers significantly inhibited UV-induced JNK activation, but not hyperosmotic-stress-induced JNK activation.
- UV-induced SEK/JNK activation was independent of extracellular calcium (Ca2+).
Conclusions:
- The SEK/JNK signaling pathway mediates UV-C irradiation-induced corneal epithelial cell apoptosis.
- Activation of this pathway is dependent on increased K+ channel activity, highlighting its role in early UV response events.