Negative control of CSL gene transcription by stress/DNA damage response and p53 [RNA-Seq]

CSL is a key transcription factor, mostly acting as a repressor. While known as main effector of Notch signaling, it can also play Notch-independent functions. Despite the wide interest in CSL, the mechanisms responsible for its own regulation have been little studied. We recently showed that CSL down-modulation in human dermal fibroblasts (HDFs) leads to conversion into cancer associated fibroblasts, which promote keratinocyte tumor development. We show here that levels of CSL gene transcription differ among HDF strains derived from many different individuals, with negative correlation with genes involved in DNA damage/repair. CSL expression in all tested strains is negatively regulated by stress / DNA damaging insults caused by UVA, Reactive Oxygen Species (ROS), smoke extract and doxorubicin treatment. p53, a key effector of the DNA damage response, functions as common negative regulator of CSL gene transcription, through both suppression of CSL promoter activity and, indirectly, through increased p21 expression. CSL was previously shown to bind p53 suppressing its activity. The present findings indicate that p53, in turn, decreases CSL expression, which can serve to enhance p53 activity in the acute response of cells to DNA damaging cancer-threatening conditions.

CSL是一类关键转录因子，主要以阻遏因子的形式发挥生物学功能。尽管其作为Notch信号通路（Notch signaling）的核心效应因子被广泛认知，但CSL亦可介导不依赖Notch信号的独立生物学功能。尽管学界对CSL的研究关注度颇高，但其自身的调控机制却鲜有探讨。我们近期的研究证实，在人类真皮成纤维细胞（human dermal fibroblasts, HDFs）中下调CSL的表达，可将其转化为癌症相关成纤维细胞，进而促进角质形成细胞源性肿瘤的发生发展。本研究发现，不同个体来源的HDF株系中，CSL基因的转录水平存在显著差异，且该转录水平与参与DNA损伤与修复的基因表达呈负相关。在所有检测的HDF株系中，CSL的表达均受到各类应激与DNA损伤刺激的负向调控，这些刺激包括长波紫外线（UVA）、活性氧（Reactive Oxygen Species, ROS）、烟雾提取物以及阿霉素处理。p53作为DNA损伤应答通路的核心效应因子，可通过双重机制负向调控CSL的基因转录：一方面直接抑制CSL基因启动子的转录活性，另一方面通过上调p21的表达间接发挥调控作用。既往研究已证实，CSL可结合p53并抑制其活性。本研究结果表明，p53可反向下调CSL的表达，这一机制能够在细胞应对DNA损伤等致癌威胁性应激的急性应答过程中，增强p53自身的活性。