College of Pharmacy and Research Institute of Pharmaceutical Sciences, Seoul National University, Seoul 151-742, Republic of Korea.
Environ Mol Mutagen. 2011 Mar;52(2):145-52. doi: 10.1002/em.20593.
Human cadmium (Cd) exposure is associated with cancers of the lung and kidney. Using cDNA microarray analysis, we have recently reported that the expression of E2F1 is reduced by Cd in human lung fibroblasts, indicating the possibility of G1-phase arrest. To test this hypothesis, we investigated the effects of Cd on the cyclin-dependent kinase (CDK2) and retinoblastoma protein (Rb) regulatory pathways in WI38 human lung fibroblasts. We demonstrate here that G1-phase accumulation was induced by Cd in WI38 (wild-type for p53 and Rb), but not in the SV40 large T antigen-transformed variant WI38-VA13 (p53- and Rb-defective). Cd-induced cell-cycle arrest was associated with a decrease in CDK2 protein and with increase in p21 expression and p53 phosphorylation. Cd treatment caused a distinct increase in the formation of p21-cyclin E-CDK2 complex, as revealed by immunoprecipitation. The level of Rb-E2F1 complexes was increased, and the translocation of E2F1 to the nucleus was decreased by Cd treatment. Consequently, the transcriptional activity of E2F1 and the expression of the E2F1 target genes were also decreased by Cd. These results clearly demonstrate that Cd-mediated G1 arrest in WI38 cells is associated with the suppression of Rb phosphorylation and with the inhibition of E2F1 transcriptional activity.
人类镉（Cd）暴露与肺癌和肾癌有关。使用 cDNA 微阵列分析，我们最近报道 Cd 可降低人肺成纤维细胞中 E2F1 的表达，表明可能发生 G1 期阻滞。为了验证这一假说，我们研究了 Cd 对 WI38 人肺成纤维细胞中细胞周期蛋白依赖性激酶（CDK2）和视网膜母细胞瘤蛋白（Rb）调节途径的影响。我们在此证明，Cd 在 WI38（p53 和 Rb 为野生型）中诱导 G1 期积累，但在 SV40 大 T 抗原转化的变体 WI38-VA13（p53 和 Rb 缺失）中则没有。Cd 诱导的细胞周期阻滞与 CDK2 蛋白减少和 p21 表达增加以及 p53 磷酸化有关。Cd 处理会导致 p21-周期蛋白 E-CDK2 复合物的形成明显增加，这通过免疫沉淀得到证实。Cd 处理还会增加 Rb-E2F1 复合物的水平，并减少 E2F1 向核内的易位。因此，Cd 还会降低 E2F1 的转录活性和 E2F1 靶基因的表达。这些结果清楚地表明，Cd 介导的 WI38 细胞 G1 期阻滞与 Rb 磷酸化的抑制和 E2F1 转录活性的抑制有关。
