Posgrado en Biología Experimental, Departamento de Ciencias de la Salud, Universidad Autónoma Metropolitana, Mexico City, Mexico.
Laboratorio de Oncología Experimental, Instituto Nacional de Pediatría, Mexico City, Mexico.
Cell Biochem Funct. 2021 Jun;39(4):478-487. doi: 10.1002/cbf.3612. Epub 2020 Dec 30.
Low levels of oxygen (hypoxia) have been reported in solid tumours. This hypoxic microenvironment modulates the expression of genes linked to a more aggressive disease. However, it is unclear if the expression of drug-metabolizing enzymes as cytochromes P450 (CYPs) is affected by hypoxia in cancer. We aimed to define which cytochromes are affected by hypoxia using a liver cancer model in vitro. For this purpose, we assessed whole-genome expression microarrays of HepG2 liver cancer cell line from free repository databases, looking for gene expression hypoxia-associated profiles and selected those cytochromes with significant differences. Then, we corroborated their mRNA expression and protein levels by RT-qPCR and western blot, respectively, as well as immunofluorescence. Based on microarray analysis, we found that the expression of CYP2S1 and CYP24A1 were up-regulated with at least twice fold change compared with normoxia. The levels of mRNA and protein of CYP2S1 and CYP24A1 were increased significantly in hypoxic conditions (P < .05), and this tendency was also observed by immunofluorescence assays. Our data show that the expression of cytochromes CYP2S1 and CYP24A1 are induced in hypoxia, being the first time that CYP24A1 expression is associated with tumour hypoxia; which might have consequences in cancer progression and drug resistance. SIGNIFICANCE OF THE STUDY: Hypoxia is among the most important factors for cellular adaptation to stress. Especially in cancer, a major public health issue, hypoxia plays a substantial role in angiogenesis, metastasis and resistance to therapy. Tumoral hypoxia has been described at least in the brain, breast, cervical, liver, renal, lung, pancreatic and renal cancer. However, the understanding of how hypoxia drives cancer progression is still a major challenge. One emerging question is the role of hypoxia over the expression of drug-metabolizing enzymes, with a significant impact on drug treatment. In this context, our paper focus on the effect of hypoxia on CYPs, which is an essential group of drug-metabolizing enzymes. We show that hypoxia induces the expression of two members of the CYPs family: CYP2S1 and CYP24A1. Importantly, CYP2S1 is a major metabolizer of carcinogenic substances being relevant that hypoxia could promote this function. Interestingly, CYP24A1 limits the action of the active form of vitamin D, which is an anti-proliferative factor in cancer. Our evidence shows for the first time that hypoxia can induce CYP24A1 expression, with a potential effect on cancer progression. Our contribution clarifies a particular effect of tumoral hypoxia and the implications will be useful in the understanding of the progression of cancer, the resistance to treatment and the development of alternative therapies.
低氧水平（缺氧）已在实体瘤中报道。这种缺氧微环境调节与更具侵袭性疾病相关的基因表达。然而，尚不清楚细胞色素 P450（CYPs）等药物代谢酶的表达是否受癌症中的缺氧影响。我们旨在使用体外肝癌模型来确定哪些细胞色素受缺氧影响。为此，我们从免费资源库数据库评估了 HepG2 肝癌细胞系的全基因组表达微阵列，寻找与基因表达缺氧相关的图谱，并选择那些差异显著的细胞色素。然后，我们通过 RT-qPCR 和 Western blot 分别验证了它们的 mRNA 表达和蛋白水平，以及免疫荧光。基于微阵列分析，我们发现与常氧相比，CYP2S1 和 CYP24A1 的表达至少增加了两倍。在缺氧条件下，CYP2S1 和 CYP24A1 的 mRNA 和蛋白水平显著增加（P <.05），免疫荧光试验也观察到了这种趋势。我们的数据表明，细胞色素 CYP2S1 和 CYP24A1 的表达在缺氧时被诱导，这是 CYP24A1 表达与肿瘤缺氧相关的首次报道；这可能对癌症进展和耐药性产生影响。研究的意义：缺氧是细胞适应应激的最重要因素之一。特别是在癌症这一重大公共卫生问题中，缺氧在血管生成、转移和对治疗的抵抗中起着重要作用。肿瘤缺氧至少在脑、乳腺、宫颈、肝、肾、肺、胰腺和肾肿瘤中已被描述。然而，了解缺氧如何驱动癌症进展仍然是一个重大挑战。一个新兴问题是缺氧对药物代谢酶表达的影响，这对药物治疗有重大影响。在这种情况下，我们的论文侧重于缺氧对细胞色素 P450（CYP）的影响，CYP 是药物代谢酶的重要组成部分。我们表明，缺氧诱导了 CYP 家族的两个成员：CYP2S1 和 CYP24A1 的表达。重要的是，CYP2S1 是致癌物质的主要代谢物，而缺氧可能促进这种功能。有趣的是，CYP24A1 限制了维生素 D 活性形式的作用，维生素 D 是癌症中的一种抗增殖因子。我们的证据首次表明，缺氧可以诱导 CYP24A1 的表达，这可能对癌症进展产生影响。我们的贡献阐明了肿瘤缺氧的特定作用，这将有助于理解癌症的进展、治疗的耐药性和替代疗法的发展。
