van de Glind Gerline C, Rebel Heggert G, Out-Luiting Jacoba J, Zoutman Wim, Tensen Cornelis P, de Gruijl Frank R
Department of Dermatology, LUMC, Leiden, The Netherlands.
Oncotarget. 2016 Dec 27;7(52):86740-86754. doi: 10.18632/oncotarget.13436.
Lgr6+ cells have been identified as a novel class of proliferating (Ki67+) stem cells in mouse epidermis. We investigated their response to UV exposure in Lgr6-EGFP-Ires-CreERT2/R26R-LacZ haired and hairless mice and whether they become initiating cells of UV- or chemically induced skin tumors. UV overexposure erased Lgr6+ cells (EGFP+) from the interfollicular epidermis (IFE), but - as after wounding - they apparently repopulated the IFE from the hair follicles. Under sub-sunburn chronic UV exposure, Lgr6+ cells and their progeny (LacZ+ after pulse of tamoxifen) diminished strongly in the IFE. Although the inter-tumoral IFE clearly showed Lgr6 progeny, none of the UV- or chemically induced tumors (n = 22 and 41, respectively) appeared to be clonal expansions of Lgr6+ stem cells; i.e. no Lgr6+ cells or progeny in the proliferating tumor bulk. In checking for promoter methylation we found it to occur stochastically for the EGFP-Cre cassette. Lgr6 mRNA measured by qPCR was found to be diminished in skin tumors (also in UV tumors from wt type mice). The ratio of Lgr6/Ki67 was significantly reduced, pointing at a loss of Lgr6+ cells from the proliferative pool. Our data show that Lgr6+ cells are not major tumor-initiating cells in skin carcinogenesis.
Lgr6+细胞已被鉴定为小鼠表皮中一类新的增殖性（Ki67+）干细胞。我们研究了Lgr6-EGFP-Ires-CreERT2/R26R-LacZ有毛和无毛小鼠中它们对紫外线照射的反应，以及它们是否会成为紫外线或化学诱导的皮肤肿瘤的起始细胞。紫外线过度照射使毛囊间表皮（IFE）中的Lgr6+细胞（EGFP+）消失，但与受伤后一样，它们显然从毛囊重新填充了IFE。在亚晒伤慢性紫外线照射下，Lgr6+细胞及其后代（他莫昔芬脉冲后LacZ+）在IFE中显著减少。尽管肿瘤间的IFE明显显示有Lgr6后代，但紫外线或化学诱导的肿瘤（分别为n = 22和41）似乎都不是Lgr6+干细胞的克隆扩增；即增殖的肿瘤块中没有Lgr6+细胞或后代。在检查启动子甲基化时，我们发现EGFP-Cre盒随机发生甲基化。通过qPCR测量发现皮肤肿瘤（包括野生型小鼠的紫外线诱导肿瘤）中Lgr6 mRNA减少。Lgr6/Ki67的比率显著降低，表明增殖池中Lgr6+细胞丢失。我们的数据表明，Lgr6+细胞不是皮肤癌发生中的主要肿瘤起始细胞。
