Tam Hann W, Hall Jonathan R, Messenger Zachary J, Jima Dereje D, House John S, Linder Keith, Smart Robert C
Toxicology Program, North Carolina State University, Raleigh, NC, USA.
Center for Human Health and the Environment, North Carolina State University, Raleigh, NC, USA.
Carcinogenesis. 2019 Sep 18;40(9):1099-1109. doi: 10.1093/carcin/bgz012.
p53 is activated by DNA damage and oncogenic stimuli to regulate senescence, apoptosis and cell-cycle arrest, which are essential to prevent cancer. Here, we utilized UVB radiation, a potent inducer of DNA damage, p53, apoptosis and skin cancer to investigate the mechanism of CCAAT/enhancer binding protein-β (C/EBPβ) in regulating p53-mediated apoptosis in keratinocytes and to test whether the deletion of C/EBPβ in epidermis can protect mice from UVB-induced skin cancer. UVB-treatment of C/EBPβ skin conditional knockout (CKOβ) mice increased p53 protein levels in epidermis and enhanced p53-dependent apoptotic activity 3-fold compared with UVB-treated control mice. UVB increased C/EBPβ levels through a p53-dependent pathway and stimulated the formation of a C/EBPβ-p53 protein complex; knockdown of C/EBPβ increased p53 protein stability in keratinocytes. These results suggest a p53-C/EBPβ feedback loop, whereby C/EBPβ, a transcriptional target of a p53 pathway, functions as a survival factor by negatively regulating p53 apoptotic activity in response to DNA damage. RNAseq analysis of UVB-treated CKOβ epidermis unexpectedly revealed that type 1 interferon (IFN) pathway was the most highly enriched pathway. Numerous pro-apoptotic interferon stimulated genes were upregulated including some known to enhance p53 apoptosis. Our results indicate that p53 and IFN pathways function together in response to DNA damage to result in the activation of extrinsic apoptosis pathways and caspase 8 cleavage. Last, we observed CKOβ mice were resistant to UVB-induced skin cancer. Our results suggest that C/EBPβ represses apoptosis through keratinocyte autonomous suppression of the type 1 IFN response and p53 to increase cell survival and susceptibility to UVB-induced skin cancer.
p53可被DNA损伤和致癌刺激激活，从而调节衰老、凋亡和细胞周期停滞，这些对于预防癌症至关重要。在此，我们利用紫外线B（UVB）辐射（一种强大的DNA损伤、p53、凋亡和皮肤癌诱导剂）来研究CCAAT/增强子结合蛋白β（C/EBPβ）调节角质形成细胞中p53介导的凋亡的机制，并测试表皮中C/EBPβ的缺失是否能保护小鼠免受UVB诱导的皮肤癌。与UVB处理的对照小鼠相比，UVB处理C/EBPβ皮肤条件性敲除（CKOβ）小鼠可增加表皮中p53蛋白水平，并增强p53依赖性凋亡活性3倍。UVB通过p53依赖性途径增加C/EBPβ水平，并刺激形成C/EBPβ-p53蛋白复合物；敲低C/EBPβ可增加角质形成细胞中p53蛋白的稳定性。这些结果提示了一个p53-C/EBPβ反馈环，即作为p53途径转录靶点的C/EBPβ通过负调节p53对DNA损伤的凋亡活性而发挥存活因子的作用。对UVB处理的CKOβ表皮进行RNA测序分析意外发现，1型干扰素（IFN）途径是最高度富集的途径。许多促凋亡干扰素刺激基因上调，包括一些已知可增强p53凋亡的基因。我们的结果表明，p53和IFN途径在响应DNA损伤时共同发挥作用，导致外源性凋亡途径的激活和半胱天冬酶8的切割。最后，我们观察到CKOβ小鼠对UVB诱导的皮肤癌具有抗性。我们的结果提示，C/EBPβ通过角质形成细胞自主抑制1型IFN反应和p53来抑制凋亡，从而增加细胞存活和对UVB诱导的皮肤癌的易感性。
