UVB Activates ERK1/2 and p38 Signaling Pathways via Reactive Oxygen Species in Cultured Keratinocytes

Abstract

We have previously shown that hydrogen peroxide is an important mediator of ultraviolet B induced phosphorylation of the epidermal growth factor receptor in human keratinocytes. Here we demonstrate that physiologic doses of ultraviolet B and hydrogen peroxide stimulate activation of two related but distinct mitogen-activated protein kinase pathways: extracellular regulated kinase 1 and 2 (ERK1/2), as well as p38, the mammalian homolog of HOG1 in yeast which is a major kinase for a recently identified stress-induced signaling pathway. The time-dependent activation of ERK1/2 and p38 are distinct, and ultraviolet B-induced ERK1/2 activation is downregulated more rapidly than p38. Using dihydrorhodamine or Amplex as specific fluorescent dye probes, we show that ultraviolet B-induced peroxides can be inhibited by ascorbic acid. Ascorbic acid strongly blocks ERK1/2 and p38 activation by ultraviolet B and hydrogen peroxide whereas pyrrolidine dithiocarbamate and butyl hydroxyanisole are less effective. Pyrrolidine dithiocarbamate was unable to inhibit ultraviolet B-induced p38 activation. Cell death was increased after ultraviolet B when ERK1/2 activation was attenuated by the specific inhibitor PD098059. The distinct time courses and extents of activation and inhibition of ERK1/2 and p38 indicate that these pathways are separate and regulated independently in keratinocytes. Specific types of reactive oxygen species induced by ultraviolet B as well as selective activation or inhibition of specific phosphatases may mediate these responses in keratinocytes. These findings demonstrate that reactive oxygen species are important multifunctional mediators of ultraviolet B-induced ERK1/2 and p38 signaling transduction pathways and suggest that ERK1/2 may play an important part in protecting keratinocytes from cell death following oxidative stress.

Differential phosphorylation of mitogen-activated protein kinase families by epidermal growth factor and ultraviolet B irradiation in SV40-transformed human keratinocytes

“…Peus et al reported that inhibition of ERK by PD98059 resulted in increased UVB-induced cell death [9]. ERK, however, was not significantly phosphorylated by UVB in SVHK…”

“…The In many cells including keratinocytes, UVB irradiation-induced apoptosis depends on p38 [9,17,31]. Still UVB-induced activation of ERK and JNK has been reported in normal human keratinocytes and in HaCaT cells [24].…”

“…Although the molecular basis of UV irradiation has been suggested to be associated with reactive oxygen species (ROS) [8,9], the precise signal transduction mechanisms have not been clarified. We have shown that inhibitors of caspase 1 and 3 suppress the UVB-induced apoptosis of cultured human keratinocytes [10,11].…”

“…MAP kinases phosphorylate and regulate the activity of various enzymes and transcription factors including the EGF receptor, Rsk 90, -5 -phospholipase A2, Elk-1, c-Myc, ATF2, and c-Jun. In keratinocytes, recent studies have shown that p38 activation is essential for UVB irradiation-induced apoptosis [17] and that the inhibition of ERK phosphorylation augments the UVB-induced apoptosis [9].…”

Obesity increases the risk of UV radiation-induced oxidative stress and activation of MAPK and NF-κB signaling

“…The phosphorylation of the MAPK proteins, namely, ERK1/2, JNK and p38, has been shown to be mediated through UVB-induced oxidative stress [17,32,33]. We examined UVB-induced phosphorylation of MAPK proteins using densitometric analysis of western blots and expressed the data in terms of the ratio of the levels of phosphorylated MAPK to the levels of the unphosphorylated form.…”