Department of Environmental Medicine, University of Rochester School of Medicine and Dentistry, Rochester, NY 14642, USA.
Mol Pharmacol. 2012 May;81(5):669-78. doi: 10.1124/mol.111.077305. Epub 2012 Feb 6.
The aryl hydrocarbon receptor (AhR), a ligand-activated member of the basic helix-loop-helix (bHLH)/PER-ARNT-SIM (PAS) transcription superfamily, is known to regulate the toxicity of polyaromatic halogenated hydrocarbon environmental chemicals, most notably dioxin. However, the AhR has also been implicated in multiple stages of tumorigenesis. Medulloblastoma (MB), a primary cerebellar brain tumor arising in infants and children, is thought to originate from abnormally proliferating cerebellar granule neuron precursors (GNPs). GNPs express high levels of the AhR in the external germinal layer of the developing cerebellum. Moreover, our laboratory has previously reported that either abnormal activation or deletion of the AhR leads to dysregulation of GNP cell cycle activity and maturation. These observations led to the hypothesis that the AhR promotes the growth of MB. Therefore, this study evaluated whether the AhR serves a pro-proliferative role in an immortalized MB tumor cell line (DAOY). We produced a stable AhR knockdown DAOY cell line [AhR short hairpin RNA (shRNA)], which exhibited a 70% reduction in AhR protein levels. Compared with wild-type DAOY cells, AhR shRNA DAOY cells displayed an impaired G(1)-to-S cell cycle transition, decreased DNA synthesis, and reduced proliferation. Furthermore, these cell cycle perturbations were correlated with decreased levels of the pro-proliferative gene Hes1 and increased levels of the cell cycle inhibitor p27(kip1). Supplementation experiments with human AhR restored the proliferative activity in AhR shRNA DAOY cells. Taken together, our data show that the AhR promotes proliferation of MB cells, suggesting that this pathway should be considered as a potential therapeutic target for MB treatment.
芳香烃受体 (AhR) 是碱性螺旋-环-螺旋 (bHLH)/PER-ARNT-SIM (PAS) 转录超家族的配体激活成员，已知其可调节多环卤代芳烃环境化学物质（尤其是二恶英）的毒性。然而，AhR 也与肿瘤发生的多个阶段有关。髓母细胞瘤 (MB) 是一种起源于婴儿和儿童小脑的原发性脑肿瘤，被认为起源于异常增殖的小脑颗粒神经元前体 (GNP)。GNP 在发育中的小脑外颗粒层表达高水平的 AhR。此外，我们实验室之前曾报道，AhR 的异常激活或缺失会导致 GNP 细胞周期活动和成熟失调。这些观察结果导致了 AhR 促进 MB 生长的假说。因此，本研究评估了 AhR 是否在永生化 MB 肿瘤细胞系 (DAOY) 中发挥促增殖作用。我们产生了稳定的 AhR 敲低 DAOY 细胞系 [AhR 短发夹 RNA (shRNA)]，其 AhR 蛋白水平降低了 70%。与野生型 DAOY 细胞相比，AhR shRNA DAOY 细胞的 G1 期至 S 期细胞周期转换受损，DNA 合成减少，增殖减少。此外，这些细胞周期扰动与促增殖基因 Hes1 水平降低和细胞周期抑制剂 p27(kip1) 水平升高相关。用人类 AhR 进行补充实验恢复了 AhR shRNA DAOY 细胞的增殖活性。综上所述，我们的数据表明 AhR 促进 MB 细胞的增殖，表明该途径应被视为 MB 治疗的潜在治疗靶点。
