Ibuki Yuko, Akaike Marie, Toyooka Tatsushi, Goto Rensuke
Laboratory of Radiation Biology, Graduate School of Nutritional and Environmental Sciences, University of Shizuoka, Shizuoka-shi, Japan.
Photochem Photobiol. 2008 Jan-Feb;84(1):154-61. doi: 10.1111/j.1751-1097.2007.00214.x.
Apoptosis is an important cell death system that deletes damaged and mutated cells to prevent cancer. We have previously reported that a certain dose of UVB irradiation inhibited the apoptosis induced by serum starvation and cell detachment, leading to cell transformation. This antiapoptotic effect was partially inhibited by phosphatidylinositol 3-kinase (PI3-kinase) inhibitors. UVB irradiation is known to cause the phosphorylation of Akt via the activation of PI3-kinase; however, the Akt isoform-specific relationship has not yet been clarified. Notably, the role in antiapoptotic effect of UVB has yet to be elucidated. In this study, the role of Akt1 in the UVB-induced inhibition of apoptosis was examined by Akt1 knockdown using small interfering RNA (siRNA). NIH3T3 cells showed typical apoptotic cell death by serum starvation and cell detachment, which was significantly inhibited by UVB irradiation. Akt1 knockdown decreased the antiapoptotic effect of UVB. Hydrogen peroxide-induced suppression of cell death was also decreased in Akt1 knockdown cells. An antioxidant, N-acetylcysteine, inhibited the antiapoptotic effect by UVB irradiation, whereas no inhibition was observed in Akt1 knockdown cells. Furthermore, UVB-induced intracellular peroxidation was not observed in the knockdown cells, indicating that Akt1 played an important role in mediating the intracellular redox status. Treatment with insulin had a similar antiapoptotic effect as UVB irradiation involving intracellular peroxidation, which was also attenuated in Akt1 knockdown cells. These findings suggest that appropriate intracellular oxidation after UVB irradiation prevented apoptosis, a process which might be partially regulated by the production of reactive oxygen species mediated by Akt1.
细胞凋亡是一种重要的细胞死亡系统，可清除受损和突变细胞以预防癌症。我们之前报道过，一定剂量的紫外线B（UVB）照射可抑制血清饥饿和细胞脱离诱导的细胞凋亡，从而导致细胞转化。磷脂酰肌醇3激酶（PI3激酶）抑制剂可部分抑制这种抗凋亡作用。已知UVB照射可通过激活PI3激酶导致Akt磷酸化；然而，Akt亚型特异性关系尚未阐明。值得注意的是，UVB在抗凋亡作用中的角色尚未得到阐明。在本研究中，通过使用小干扰RNA（siRNA）敲低Akt1来检测Akt1在UVB诱导的凋亡抑制中的作用。NIH3T3细胞在血清饥饿和细胞脱离时表现出典型的凋亡性细胞死亡，而UVB照射可显著抑制这种死亡。敲低Akt1可降低UVB的抗凋亡作用。在敲低Akt1的细胞中，过氧化氢诱导的细胞死亡抑制也有所降低。抗氧化剂N - 乙酰半胱氨酸可抑制UVB照射的抗凋亡作用，而在敲低Akt1的细胞中未观察到抑制作用。此外，在敲低细胞中未观察到UVB诱导的细胞内过氧化，这表明Akt1在介导细胞内氧化还原状态中起重要作用。胰岛素处理具有与UVB照射类似的涉及细胞内过氧化的抗凋亡作用，在敲低Akt1的细胞中这种作用也减弱。这些发现表明，UVB照射后适当的细胞内氧化可预防凋亡，这一过程可能部分由Akt1介导的活性氧生成所调节。
