Graduate Center for Toxicology, 1095 V.A. Drive, 306 Health Sciences Research Building, Lexington, KY 40536, USA.
Toxicol Sci. 2011 Oct;123(2):399-410. doi: 10.1093/toxsci/kfr180. Epub 2011 Jul 8.
Hexavalent chromium [Cr(VI)] is a well-known human carcinogen associated with the incidence of lung cancer. Although overproduction of reactive oxygen species (ROS) has been suggested to play a major role in its carcinogenicity, the mechanisms of Cr(VI)-induced ROS production remain unclear. In this study, we investigated the role of NADPH oxidase (NOX), one of the major sources of cellular ROS, in Cr(VI)-induced oxidative stress and carcinogenesis. We found that short-term exposure to Cr(VI) (2μM) resulted in a rapid increase in ROS generation in Beas-2B cells, and concomitantly increased NOX activity and expression of NOX members (NOX1-3 and NOX5) and subunits (p22(phox), p47(phox), p40(phox), and p67(phox)). Cr(VI) also induced phosphorylation of p47(phox) and membrane translocation of p47(phox) and p67(phox), further confirming NOX activation. Knockdown of p47(phox) with a short hairpin RNA attenuated the ROS production induced by Cr(VI). Chronic exposure (up to 3 months) to low doses of Cr(VI) (0.125, 0.25, and 0.5μM) also promoted ROS generation and the expression of NOX subunits, such as p47(phox) and p67(phox), but inhibited the expression of main antioxidant enzymes, such as superoxidase dismutase (SOD) and glutathione peroxidase (GPx). Chronic Cr(VI) exposure resulted in transformation of Beas-2B cells, increasing cell proliferation, anchorage independent growth in soft agar, and forming aggressive tumors in nude mice. Stable knockdown of p47(phox) or overexpression of SOD1, SOD2, or catalase (CAT) eliminated Cr(VI)-induced malignant transformation. Our results suggest that NOX plays an important role in Cr(VI)-induced ROS generation and carcinogenesis.
六价铬[Cr(VI)]是一种众所周知的人类致癌物，与肺癌的发病率有关。尽管已经提出活性氧物种（ROS）的过度产生在其致癌性中起主要作用，但 Cr(VI)诱导的 ROS 产生的机制仍不清楚。在这项研究中，我们研究了 NADPH 氧化酶（NOX）作为细胞 ROS 的主要来源之一在 Cr(VI)诱导的氧化应激和致癌作用中的作用。我们发现，短期暴露于 Cr(VI)（2μM）会导致 Beas-2B 细胞中 ROS 的产生迅速增加，同时增加 NOX 活性和 NOX 成员（NOX1-3 和 NOX5）和亚基（p22(phox)、p47(phox)、p40(phox)和 p67(phox)）的表达。Cr(VI)还诱导 p47(phox)的磷酸化和 p47(phox)和 p67(phox)的膜转位，进一步证实了 NOX 的激活。用短发夹 RNA 敲低 p47(phox)可减弱 Cr(VI)诱导的 ROS 产生。慢性暴露（长达 3 个月）于低剂量的 Cr(VI)（0.125、0.25 和 0.5μM）也促进 ROS 的产生和 NOX 亚基的表达，如 p47(phox)和 p67(phox)，但抑制主要抗氧化酶的表达，如超氧化物歧化酶（SOD）和谷胱甘肽过氧化物酶（GPx）。慢性 Cr(VI)暴露导致 Beas-2B 细胞转化，增加细胞增殖、软琼脂中的无锚定生长以及在裸鼠中形成侵袭性肿瘤。p47(phox)的稳定敲低或 SOD1、SOD2 或过氧化氢酶（CAT）的过表达消除了 Cr(VI)诱导的恶性转化。我们的结果表明，NOX 在 Cr(VI)诱导的 ROS 产生和致癌作用中起重要作用。
