Centro de Investigaciones Oncológicas de la Fundación Cáncer, 1426 Buenos Aires, Argentina.
Hum Pathol. 2012 Feb;43(2):197-208. doi: 10.1016/j.humpath.2011.04.015. Epub 2011 Aug 4.
Metallothioneins are a family of small, cysteine-rich proteins with many functions. Immunohistochemical evaluation of all metallothionein 1 + 2 isoforms in colorectal tumors has demonstrated an important down-regulation compared with normal tissue, although its prognostic significance is unclear. Moreover, the contribution of individual isoforms to overall metallothionein down-regulation is not known. To address these important issues, we analyzed the messenger RNA expression levels of all functional metallothionein 1 + 2 isoforms by quantitative reverse transcription polymerase chain reaction in 22 pairs of normal and tumor-microdissected epithelia and correlated these to the overall immunohistochemical protein expression. Our results showed that 5 isoforms (MT1G, 1E, 1F, 1H, and 1M) were lost during the transition from normal mucosa to tumor, whereas MT1X and MT2A were less down-regulated, and their expression was correlated with overall protein positivity. Second, we showed that MT1G hypermethylation occurred in cell lines and in 29% of tumor samples, whereas histone deacetylase inhibitors are able to induce most isoforms. Furthermore, we analyzed by immunohistochemistry 107 normal mucosae, 25 adenomas, 81 carcinomas, and 19 lymph node metastases to evaluate metallothionein expression during different stages of cancer development and to assess its relationship to patient survival. A lower immunohistochemical expression was associated with poorer survival, although it was not an independent predictor. Overall, this study identifies for the first time the relevant metallothionein isoforms for colorectal cancer progression, supports the concept that their loss is associated with worse prognosis, and suggests 2 mechanisms for epigenetic repression of metallothionein expression in colorectal tumors.
金属硫蛋白是一类具有多种功能的小分子、富含半胱氨酸的蛋白质。对结直肠肿瘤中所有金属硫蛋白 1+2 同工型的免疫组织化学评估表明，与正常组织相比，其表达显著下调，但其预后意义尚不清楚。此外，个体同工型对整体金属硫蛋白下调的贡献尚不清楚。为了解决这些重要问题，我们通过定量逆转录聚合酶链反应分析了 22 对正常和肿瘤微切割上皮中的所有功能性金属硫蛋白 1+2 同工型的信使 RNA 表达水平，并将其与整体免疫组织化学蛋白表达相关联。我们的结果表明，在正常黏膜向肿瘤过渡的过程中，有 5 种同工型（MT1G、1E、1F、1H 和 1M）丢失，而 MT1X 和 MT2A 的下调程度较低，其表达与整体蛋白阳性相关。其次，我们表明 MT1G 甲基化发生在细胞系和 29%的肿瘤样本中，而组蛋白去乙酰化酶抑制剂能够诱导大多数同工型。此外，我们通过免疫组织化学分析了 107 例正常黏膜、25 例腺瘤、81 例癌和 19 例淋巴结转移，以评估金属硫蛋白在癌症发展不同阶段的表达，并评估其与患者生存的关系。较低的免疫组织化学表达与较差的生存相关，尽管它不是独立的预测因子。总的来说，这项研究首次确定了与结直肠癌进展相关的重要金属硫蛋白同工型，支持了其缺失与预后较差相关的概念，并提出了结直肠肿瘤中金属硫蛋白表达的 2 种表观遗传抑制机制。
