Zykova Tatyana A, Zhu Feng, Zhang Yiguo, Bode Ann M, Dong Zigang
Hormel Institute, University of Minnesota, 801 16th Avenue NE, Austin, MN 55912, USA.
Carcinogenesis. 2007 Jul;28(7):1543-51. doi: 10.1093/carcin/bgm070. Epub 2007 Apr 2.
Double-stranded RNA-dependent protein kinase R (PKR) has been implicated in anti-viral (antitumor) and apoptotic responses. PKR is activated by extracellular stresses and phosphorylates the alpha subunit of protein synthesis initiation factor eIF2, thereby inhibiting protein synthesis and impeding virus multiplication. Phosphorylation of eIF2alpha in mammalian cells has been shown to be increased after ultraviolet (UV) stress and to be required for UV-induced repression of protein translation. UVA is an important etiological factor in skin carcinogenesis and we observed that UVA induced phosphorylation of PKR (Thr(451)) and eIF2alpha (Ser(51)) in mouse skin epidermal JB6 Cl41 cells. The induction was suppressed by the MEK1 inhibitor, PD 98059. UVA stimulation of PKR and eIF2alpha phosphorylation was also inhibited by a dominant-negative mutant (DNM) of ERK2- or RSK2-deficient cells (RSK2(-)). An inhibitor of p38, SB 202190 or a DNM of p38alpha kinase (DNM-p38alpha) suppressed UVA-induced phosphorylation of eIF2alpha (Ser(51)) but had no effect on phosphorylation of PKR (Thr(451)). Our data indicated that phosphorylation of PKR at Thr(451) is mediated through ERK2 and RSK2, but not through p38 kinase, and is involved in the regulation of Ser(51) phosphorylation of eIF2alpha in UVA-irradiated JB6 cells. In vitro and in vivo kinase assays indicated that phosphorylation of eIF2alpha at Ser(51) occurred indirectly through ERK2, RSK2 or p38 kinase in the cellular response to UVA. These data may lead to the use of these signaling molecules as targets to develop more effective chemopreventive agents with fewer side effects to control UV-induced skin cancer.
双链RNA依赖蛋白激酶R（PKR）与抗病毒（抗肿瘤）和凋亡反应有关。PKR被细胞外应激激活，并使蛋白质合成起始因子eIF2的α亚基磷酸化，从而抑制蛋白质合成并阻碍病毒增殖。在哺乳动物细胞中，紫外线（UV）应激后eIF2α的磷酸化已被证明会增加，并且是UV诱导的蛋白质翻译抑制所必需的。UVA是皮肤致癌的一个重要病因，我们观察到UVA在小鼠皮肤表皮JB6 Cl41细胞中诱导PKR（Thr(451)）和eIF2α（Ser(51)）磷酸化。MEK1抑制剂PD 98059可抑制这种诱导。ERK2或RSK2缺陷细胞（RSK2(-)）的显性负突变体（DNM）也可抑制UVA对PKR和eIF2α磷酸化的刺激。p38抑制剂SB 202190或p38α激酶的DNM（DNM-p38α）可抑制UVA诱导的eIF2α（Ser(51)）磷酸化，但对PKR（Thr(451)）磷酸化没有影响。我们的数据表明，Thr(451)处PKR的磷酸化是通过ERK2和RSK2介导的，而不是通过p38激酶介导的，并且参与了UVA照射的JB6细胞中eIF2α Ser(51)磷酸化的调节。体外和体内激酶分析表明，在细胞对UVA的反应中，Ser(51)处eIF2α的磷酸化是通过ERK2、RSK2或p38激酶间接发生的。这些数据可能会导致将这些信号分子用作靶点，以开发出更有效的化学预防剂，其副作用更少，用于控制UV诱导的皮肤癌。
