Department of Pathology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA.
Mol Carcinog. 2012 Sep;51(9):734-45. doi: 10.1002/mc.20840. Epub 2011 Aug 18.
UVB radiation is the major carcinogen responsible for skin carcinogenesis, thus elucidation of the molecular pathways altered in skin in response to UVB would reveal novel targets for therapeutic intervention. It is well established that UVB leads to upregulation of cyclooxygenase 2 (COX-2) in the skin which contributes to skin carcinogenesis. Overexpression of COX-2 has been shown to promote colon cancer cell growth through β-catenin signaling, however, little is known about the connection between UVB, COX-2, and β-catenin in the skin. In the present study, we have identified a novel pathway in which UVB induces β-catenin signaling in keratinocytes, which is modulated by COX-2 expression. Exposure of the mouse 308 keratinocyte cell line (308 cells) and primary normal human epidermal keratinocytes (NHEKs) to UVB resulted in increased protein levels of both N-terminally unphosphorylated and total β-catenin. In addition, we found that UVB-enhanced β-catenin-dependent TOPflash reporter activity and expression of a downstream β-catenin target gene. We demonstrated that UVB-induced β-catenin signaling is modulated by COX-2, as treatment of keratinocytes with the specific COX-2 inhibitor NS398 blocked UVB induction of β-catenin. Additionally, β-catenin target gene expression was reduced in UVB-treated COX-2 knockout (KO) MEFs compared to wild-type (WT) MEFs. Furthermore, epidermis from UVB-exposed SKH-1 mice exhibited increased N-terminally unphosphorylated and total β-catenin protein levels and increased staining for total β-catenin, and both responses were reduced in COX-2 heterozygous mice. Taken together, these results suggest a novel pathway in which UVB induces β-catenin signaling in keratinocytes which is enhanced by COX-2 expression.
UVB 辐射是导致皮肤癌变的主要致癌物质，因此阐明皮肤对 UVB 反应中改变的分子途径将揭示治疗干预的新靶点。众所周知，UVB 导致皮肤中环氧化酶 2（COX-2）的上调，这有助于皮肤癌变。COX-2 的过表达已被证明通过β-连环蛋白信号促进结肠癌细胞生长，然而，关于 UVB、COX-2 和β-连环蛋白在皮肤中的联系知之甚少。在本研究中，我们已经确定了一条新途径，即 UVB 在角质细胞中诱导β-连环蛋白信号，该信号受 COX-2 表达的调节。暴露于小鼠 308 角质细胞系（308 细胞）和原代正常人表皮角质细胞（NHEKs）中的 UVB 导致未磷酸化的 N 端和总β-连环蛋白的蛋白水平增加。此外，我们发现 UVB 增强了β-连环蛋白依赖性 TOPflash 报告基因活性和下游β-连环蛋白靶基因的表达。我们证明了 UVB 诱导的β-连环蛋白信号受 COX-2 调节，因为角质细胞用特异性 COX-2 抑制剂 NS398 处理可阻断 UVB 诱导的β-连环蛋白。此外，与野生型（WT）MEFs 相比，UVB 处理的 COX-2 敲除（KO）MEFs 中β-连环蛋白靶基因的表达减少。此外，暴露于 UVB 的 SKH-1 小鼠的表皮显示出增加的未磷酸化的 N 端和总β-连环蛋白蛋白水平以及总β-连环蛋白的增加染色，这两种反应在 COX-2 杂合子小鼠中均减少。总之，这些结果表明了一条新途径，即 UVB 在角质细胞中诱导β-连环蛋白信号，该信号受 COX-2 表达增强。
