Department of Dermatology, TU Dresden, 01307 Dresden, Germany.
Int J Mol Sci. 2013 Jul 24;14(8):15260-85. doi: 10.3390/ijms140815260.
Induction of DNA damage by UVB and UVA radiation may generate mutations and genomic instability leading to carcinogenesis. Therefore, skin cells being repeatedly exposed to ultraviolet (UV) light have acquired multilayered protective mechanisms to avoid malignant transformation. Besides extensive DNA repair mechanisms, the damaged skin cells can be eliminated by induction of apoptosis, which is mediated through the action of tumor suppressor p53. In order to prevent the excessive loss of skin cells and to maintain the skin barrier function, apoptotic pathways are counteracted by anti-apoptotic signaling including the AKT/mTOR pathway. However, AKT/mTOR not only prevents cell death, but is also active in cell cycle transition and hyper-proliferation, thereby also counteracting p53. In turn, AKT/mTOR is tuned down by the negative regulators being controlled by the p53. This inhibition of AKT/mTOR, in combination with transactivation of damage-regulated autophagy modulators, guides the p53-mediated elimination of damaged cellular components by autophagic clearance. Alternatively, p53 irreversibly blocks cell cycle progression to prevent AKT/mTOR-driven proliferation, thereby inducing premature senescence. Conclusively, AKT/mTOR via an extensive cross talk with p53 influences the UV response in the skin with no black and white scenario deciding over death or survival.
UVB 和 UVA 辐射引起的 DNA 损伤可能导致突变和基因组不稳定,从而引发癌症。因此,反复暴露于紫外线 (UV) 下的皮肤细胞已获得多层保护机制以避免恶性转化。除了广泛的 DNA 修复机制外,受损的皮肤细胞还可以通过肿瘤抑制因子 p53 的作用诱导细胞凋亡来消除。为了防止皮肤细胞的过度流失并维持皮肤屏障功能,凋亡途径会被包括 AKT/mTOR 途径在内的抗凋亡信号抵消。然而,AKT/mTOR 不仅可以防止细胞死亡,而且还可以在细胞周期转换和过度增殖中发挥作用,从而也可以抵消 p53。反过来,AKT/mTOR 又受到 p53 控制的负调控因子的调控。这种 AKT/mTOR 的抑制作用,结合损伤调节自噬调节剂的转录激活,指导 p53 介导的通过自噬清除受损细胞成分的消除。或者,p53 不可逆地阻止细胞周期进程,以防止 AKT/mTOR 驱动的增殖,从而诱导过早衰老。总之,AKT/mTOR 通过与 p53 的广泛交叉对话影响皮肤对紫外线的反应,不存在决定生死的黑白场景。