Ultraviolet irradiation-induced K+ channel activity involving p53 activation in corneal epithelial cells

Abstract

Recent studies from our lab found that ultraviolet (UV) irradiation induces a voltage-gated potassium (Kv) channel activation and subsequently activates JNK signaling pathway resulting in apoptosis. The present study in rabbit corneal epithelial (RCE) cells is to investigate mechanisms of UV irradiation-induced Kv channel activity involving p53 activation in parallel to DNA damage-induced signaling pathway. UV irradiationinduced signaling events were characterized by measurements of JNK activation and further downstream p53 phosphorylation. UV irradiation elicited an early response in the cell membrane through activation of Kv channels to activate the JNK signaling pathway and p53 phosphorylation. Exposure of RCE cells to UV irradiation within a few min resulted in JNK and p53 activations that were markedly inhibited by suppression of Kv channel activity. However, suppression of Kv channel activity failed to prevent p53 activation induced by extended DNA damages through prolonging UV exposure time (more than 15 min). In addition, caffeine inhibited UV-induced activation of SEK, an upstream MAPK kinase of JNK, resulting in suppression of both Kv channel-involved and DNA damage-induced p53 activation. Our results indicate in these cells that UV irradiation induces earlier and later intracellular events that link to activation of JNK and p53. The early event in response to UV irradiation is initiated by activating Kv channels in the cell membrane, and the later event is predominated by UV irradiationcaused DNA damage.

Stress-induced corneal epithelial apoptosis mediated by K+ channel activation

“…UV irradiationinduced p53ser15 phosphorylation (within 5-15 min) occurs earlier than the site of p53ser20 (in 30 min). These data are consistent to the results obtained from Western analysis of this protein (Wang et al, 2005). Immunostaining experiments reveal that UV irradiation increases phosphorylation of p53ser15 in the nuclei in 15 min, but total p53 protein levels are not changed in control cells (Fig.…”

“…However, TNF-α suppresses particular types of K + channel activity in other cell types, indicating that the effect of TNF-α on K + channel activity is dependent on the channel type and cell origins (Vicente et al, 2004;Wang J et al, 2004). In corneal epithelial cells, TNF-α does not induce apoptosis, but instead it increases the expression of p21 resulting in cell cycle attenuation in the G 1 phase (Wang et al, 2005). We, as well as others, in numerous earlier studies have shown that K + channel activity is the major conductance in the cell membrane.…”

“…Suppression of K + channel activity with 4-AP effectively prevents UV irradiation-induced SEK-1 phosphorylation. This result indicates that UV irradiation-induced increases in K + channel activity also affect early events upstream from SEK in the JNK signaling pathway Wang et al, 2005).…”

“…However, a recent study from our lab has provided new data to demonstrate that there are high expression levels of p53 protein in corneal epithelial cells. UV irradiation in these cells induces two stages (earlier and later) of cellular events that subsequently involve activation of p53 (Wang et al, 2005). Expression levels of p53 protein in hypo-phosphorylated states are highly expressed in corneal epithelial cells.…”

“…There is an other interesting observation showing that suppression of Kv channels with 4-AP (1 mM) can completely prevent UV irradiation-induced JNK activation, but only partially prevent UV irradiation-induced phosphorylation of p53ser15 (Wang et al, 2005). To understand why suppression of Kv channels only partially inhibits UV irradiation-induced p53ser15 phosphorylation in corneal epithelial cells, further investigation is conducted by using different UV stimulation protocols.…”