Jayachandran Aparna, Lo Pu-Han, Chueh Anderly C, Prithviraj Prashanth, Molania Ramyar, Davalos-Salas Mercedes, Anaka Matthew, Walkiewicz Marzena, Cebon Jonathan, Behren Andreas
Ludwig Institute for Cancer Research, Melbourne-Austin Branch, Heidelberg, VIC, 3084, Australia.
Olivia Newton-John Cancer Research Institute, Heidelberg, VIC, 3084, Australia.
BMC Cancer. 2016 Feb 22;16:134. doi: 10.1186/s12885-016-2185-5.
The metabolism of cancer cells is often reprogrammed by dysregulation of metabolic enzymes. Transketolase-like 1 (TKTL1) is a homodimeric transketolase linking the pentose-phosphate pathway with the glycolytic pathway. It is generally silenced at a transcriptional level in somatic tissues. However, in human cancers its expression is associated with the acquisition of a glycolytic phenotype (the Warburg effect) by cancer cells that contributes to the progression of malignant tumors. In melanoma, defective promoter methylation results in the expression of genes and their products that can affect the tumor cell's phenotype including the modification of immune and functional characteristics. The present study evaluates the role of TKTL1 as a mediator of disease progression in melanoma associated with a defective methylation phenotype.
The expression of TKTL1 in metastatic melanoma tumors and cell lines was analysed by qRT-PCR and immunohistochemistry. The promoter methylation status of TKTL1 in melanoma cells was evaluated by quantitative methylation specific PCR. Using qRT-PCR, the effect of a DNA demethylating agent 5-aza-2'-deoxycytidine (5aza) on the expression of TKTL1 was examined. Biochemical and molecular analyses such as glucose consumption, lactate production, invasion, proliferation and cell cycle progression together with ectopic expression and siRNA mediated knockdown were used to investigate the role of TKTL1 in melanoma cells.
Expression of TKTL1 was highly restricted in normal adult tissues and was overexpressed in a subset of metastatic melanoma tumors and derived cell lines. The TKTL1 promoter was activated by hypomethylation and treatment with 5aza induced TKTL1 expression in melanoma cells. Augmented expression of TKTL1 in melanoma cells was associated with a glycolytic phenotype. Loss and gain of function studies revealed that TKTL1 contributed to enhanced invasion of melanoma cells.
Our data provide evidence for an important role of TKTL1 in aerobic glycolysis and tumor promotion in melanoma that may result from defective promoter methylation. This epigenetic change may enable the natural selection of tumor cells with a metabolic phenotype and thereby provide a potential therapeutic target for a subset of melanoma tumors with elevated TKTL1 expression.
癌细胞的代谢常因代谢酶的失调而重新编程。转酮醇酶样1（TKTL1）是一种同型二聚体转酮醇酶，它将磷酸戊糖途径与糖酵解途径联系起来。在体细胞组织中，它通常在转录水平上沉默。然而，在人类癌症中，其表达与癌细胞获得糖酵解表型（瓦伯格效应）相关，这有助于恶性肿瘤的进展。在黑色素瘤中，启动子甲基化缺陷导致基因及其产物的表达，这些基因和产物可影响肿瘤细胞的表型，包括免疫和功能特征的改变。本研究评估了TKTL1作为与甲基化缺陷表型相关的黑色素瘤疾病进展介导因子的作用。
通过qRT-PCR和免疫组织化学分析转移性黑色素瘤肿瘤和细胞系中TKTL1的表达。通过定量甲基化特异性PCR评估黑色素瘤细胞中TKTL1的启动子甲基化状态。使用qRT-PCR，检测DNA去甲基化剂5-氮杂-2'-脱氧胞苷（5aza）对TKTL1表达的影响。通过葡萄糖消耗、乳酸产生、侵袭、增殖和细胞周期进展等生化和分子分析，以及异位表达和siRNA介导的敲低，来研究TKTL1在黑色素瘤细胞中的作用。
TKTL1的表达在正常成人组织中受到高度限制，在一部分转移性黑色素瘤肿瘤及其衍生的细胞系中过表达。TKTL1启动子通过低甲基化被激活，用5aza处理可诱导黑色素瘤细胞中TKTL1的表达。黑色素瘤细胞中TKTL1表达的增加与糖酵解表型相关。功能缺失和功能获得研究表明，TKTL1有助于增强黑色素瘤细胞的侵袭能力。
我们的数据证明了TKTL1在黑色素瘤有氧糖酵解和肿瘤促进中起重要作用，这可能是由于启动子甲基化缺陷所致。这种表观遗传变化可能使具有代谢表型的肿瘤细胞得以自然选择，从而为TKTL1表达升高的一部分黑色素瘤肿瘤提供潜在的治疗靶点。
