Vetter Elena, Kronast Mira, Tölge Mariana, Zimmermann Wolfgang
Tumour Immunology Laboratory, LIFE Centre, University Hospital, Ludwig-Maximilians University, Munich, Germany.
J Pathol. 2016 Jan;238(1):42-51. doi: 10.1002/path.4629. Epub 2015 Oct 1.
In intestinal and pyloric epithelia, leucine-rich repeat-containing G protein-coupled receptor 5 (Lgr5)-expressing cells represent long-lived adult stem cells that give rise to all epithelial cell types, including endocrine cells. Ablation of the Apc gene in Lgr5-expressing cells leads to intestinal and pyloric adenomas. To assess whether all epithelial tumours of the gastrointestinal tract are derived from LGR5-positive stem cells, we crossed Lgr5-EGFP-IRES-creER(T2) mice, which express EGFP and Cre recombinase driven by the Lgr5 promoter, with CEA424-SV40-TAg mice, which develop pyloric neuroendocrine carcinomas of epithelial origin. In 19 day-old mice, single SV40 T antigen (TAg)-positive cells were identified preferentially at the the bases of pyloric glands, close to the stem cell compartment. However, contrary to previous publications describing subpopulations of LGR5-positive cells in gastrointestinal neoplasia, we could not detect Lgr5-EGFP-positive tumour cells in malignant lesions. The lack of expression of the Wnt target gene Lgr5 is probably not caused by suppression of Wnt signalling by TAg, since β-catenin-mediated Wnt signalling, as measured by the TOPflash assay, was not inhibited. To determine the cellular origin of CEA424-SV40-TAg tumours, we performed tracing experiments using Lgr5-EGFP-IRES-creERT2:CEA424-SV40-TAg:ROSA26-tdRFP mice. Following tamoxifen induction, it was possible to efficiently trace the progeny of Lgr5-expressing cells in gastrointestinal tissue via red fluorescent protein (RFP) expression. No RFP-positive tumour cells were detected, even when RFP gene activation occurred in 7 day-old mice well before the appearance of TAg-positive tumour cells. Hence, we conclude that Lgr5-expressing stem cells probably do not constitute the cells of origin in CEA424-SV40-TAg mice. Consequently, not all epithelial tumours in the pyloric region are initiated by transformation of LGR5-positive stem cells. Thus, additional long-lived LGR5-negative stem cells or progenitor cells with a low turnover rate might exist in the pyloric region, which could give rise to tumours.
在肠道和幽门上皮中，表达富含亮氨酸重复序列的G蛋白偶联受体5（Lgr5）的细胞代表能产生包括内分泌细胞在内的所有上皮细胞类型的长寿成年干细胞。在表达Lgr5的细胞中敲除Apc基因会导致肠道和幽门腺瘤。为了评估胃肠道的所有上皮肿瘤是否都源自LGR5阳性干细胞，我们将由Lgr5启动子驱动表达EGFP和Cre重组酶的Lgr5-EGFP-IRES-creER(T2)小鼠与发生上皮源性幽门神经内分泌癌的CEA424-SV40-TAg小鼠进行杂交。在19日龄小鼠中，单个SV40 T抗原（TAg）阳性细胞优先在靠近干细胞区室的幽门腺基部被识别。然而，与之前描述胃肠道肿瘤中LGR5阳性细胞亚群的出版物相反，我们在恶性病变中未检测到Lgr5-EGFP阳性肿瘤细胞。Wnt靶基因Lgr5缺乏表达可能不是由TAg对Wnt信号的抑制引起的，因为通过TOPflash分析测定的β-连环蛋白介导的Wnt信号并未受到抑制。为了确定CEA424-SV40-TAg肿瘤的细胞起源，我们使用Lgr5-EGFP-IRES-creERT2:CEA424-SV40-TAg:ROSA26-tdRFP小鼠进行了追踪实验。在他莫昔芬诱导后，通过红色荧光蛋白（RFP）表达能够有效地追踪胃肠道组织中表达Lgr5的细胞的后代。即使RFP基因激活发生在7日龄小鼠中，远早于TAg阳性肿瘤细胞出现，也未检测到RFP阳性肿瘤细胞。因此，我们得出结论，表达Lgr5的干细胞可能不是CEA424-SV40-TAg小鼠的肿瘤起源细胞。因此，并非幽门区域的所有上皮肿瘤都是由LGR5阳性干细胞的转化引发的。因此，幽门区域可能存在其他长寿的LGR5阴性干细胞或低周转率的祖细胞，它们可能引发肿瘤。
