Instituto de Biología y Genética Molecular-Departamento de Bioquímica y Biología Molecular y Fisiología, Universidad de Valladolid-CSIC, c/ Sanz y Forés 3, 47003, Valladolid, Spain.
Int J Colorectal Dis. 2013 Jun;28(6):751-66. doi: 10.1007/s00384-012-1616-2. Epub 2013 Jan 8.
Inverse correlations of apolipoprotein D (ApoD) expression with tumor growth have been shown, therefore proposing ApoD as a good prognostic marker for diverse cancer types, including colorectal cancer (CRC). Besides, ApoD expression is boosted upon oxidative stress (OS) in many pathological situations. This study aims at understanding the role of ApoD in the progression of human CRC.
Samples of CRC and distant normal tissue (n = 51) were assayed for levels of lipid peroxidation, expression profile of OS-dependent genes, and protein expression. Three single-nucleotide polymorphisms in the ApoD gene were analyzed (n = 139), with no significant associations found. Finally, we assayed the effect of ApoD in proliferation and apoptosis in the CRC HT-29 cell line.
In CRC, lipid peroxides increase while ApoD messenger RNA and protein decrease through tumor progression, with a prominent decrease in stage I. In normal mucosa, ApoD protein is present in lamina propia and enteroendocrine cells. In CRC, ApoD expression is heterogeneous, with low expression in stromal cells commonly associated with high expression in the dysplastic epithelium. ApoD promoter is basally methylated in HT-29 cells but retains the ability to respond to OS. Exogenous addition of ApoD to HT-29 cells does not modify proliferation or apoptosis levels in control conditions, but it promotes apoptosis upon paraquat-induced OS.
Our results show ApoD as a gene responding to OS in the tumor microenvironment. Besides using ApoD as marker of initial stages of tumor progression, it can become a therapeutic tool promoting death of proliferating tumor cells suffering OS.
已有研究表明载脂蛋白 D（ApoD）的表达与肿瘤生长呈负相关，因此 ApoD 被认为是多种癌症类型（包括结直肠癌（CRC））的良好预后标志物。此外，在许多病理情况下，ApoD 的表达会因氧化应激（OS）而增加。本研究旨在探讨 ApoD 在人 CRC 进展中的作用。
检测了 51 例 CRC 及远处正常组织样本的脂质过氧化水平、OS 相关基因表达谱和蛋白表达情况。分析了 ApoD 基因中的 3 个单核苷酸多态性（n=139），但未发现显著相关性。最后，我们检测了 ApoD 在 CRC HT-29 细胞系中的增殖和凋亡作用。
在 CRC 中，随着肿瘤的进展，脂质过氧化物增加，而 ApoD 信使 RNA 和蛋白减少，在 I 期时明显减少。在正常黏膜中，ApoD 蛋白存在于固有层和肠内分泌细胞中。在 CRC 中，ApoD 表达呈异质性，基质细胞表达较低，常伴有发育不良上皮细胞的高表达。ApoD 启动子在 HT-29 细胞中呈基础甲基化，但保留对 OS 反应的能力。在 HT-29 细胞中，外源性添加 ApoD 不会改变对照条件下的增殖或凋亡水平，但在百草枯诱导的 OS 下可促进凋亡。
我们的结果表明，ApoD 是肿瘤微环境中对 OS 反应的基因。除了将 ApoD 用作肿瘤进展初始阶段的标志物外，它还可以成为一种治疗工具，促进遭受 OS 的增殖肿瘤细胞死亡。
