Department of Medicine, University of North Carolina at Chapel Hill, USA.
Am J Physiol Gastrointest Liver Physiol. 2012 Aug 15;303(4):G443-52. doi: 10.1152/ajpgi.00087.2012. Epub 2012 Jun 21.
A growing body of evidence has implicated CD24, a cell-surface protein, as a marker of colorectal cancer stem cells and target for antitumor therapy, although its presence in normal colonic epithelium has not been fully characterized. Previously, our group showed that CD24-based cell sorting can be used to isolate a fraction of murine small intestinal epithelial cells enriched in actively cycling stem cells. Similarly, we hypothesized that CD24-based isolation of colonic epithelial cells would generate a fraction enriched in actively cycling colonic epithelial stem cells (CESCs). Immunohistochemistry performed on mouse colonic tissue showed CD24 expression in the bottom half of proximal colon crypts and the crypt base in the distal colon. This pattern of distribution was similar to enhanced green fluorescent protein (EGFP) expression in Lgr5-EGFP mice. Areas expressing CD24 contained actively proliferating cells as determined by ethynyl deoxyuridine (EdU) incorporation, with a distinct difference between the proximal colon, where EdU-labeled cells were most frequent in the midcrypt, and the distal colon, where they were primarily at the crypt base. Flow cytometric analyses of single epithelial cells, identified by epithelial cell adhesion molecule (EpCAM) positivity, from mouse colon revealed an actively cycling CD24(+) fraction that contained the majority of Lgr5-EGFP(+) putative CESCs. Transcript analysis by quantitative RT-PCR confirmed enrichment of active CESC markers [leucine-rich-repeat-containing G protein-coupled receptor 5 (Lgr5), ephrin type B receptor 2 (EphB2), and CD166] in the CD24(+)EpCAM(+) fraction but also showed enrichment of quiescent CESC markers [leucine-rich repeats and immunoglobin domains (Lrig), doublecortin and calmodulin kinase-like 1 (DCAMKL-1), and murine telomerase reverse transcriptase (mTert)]. We conclude that CD24-based sorting in wild-type mice isolates a colonic epithelial fraction highly enriched in actively cycling and quiescent putative CESCs. Furthermore, the presence of CD24 expression in normal colonic epithelium may have important implications for the use of anti-CD24-based colorectal cancer therapies.
越来越多的证据表明,细胞表面蛋白 CD24 是结直肠癌细胞干细胞的标志物和抗肿瘤治疗的靶点,尽管其在正常结肠上皮中的存在尚未完全表征。以前,我们的研究小组表明,基于 CD24 的细胞分选可用于分离富含活跃循环干细胞的小鼠小肠上皮细胞。同样,我们假设基于 CD24 的结肠上皮细胞分离将产生富含活跃循环结肠上皮干细胞 (CESC) 的部分。对小鼠结肠组织进行的免疫组织化学染色显示,近端结肠隐窝的下半部分和远端结肠隐窝基底存在 CD24 表达。这种分布模式与 Lgr5-EGFP 小鼠中的增强型绿色荧光蛋白 (EGFP) 表达相似。通过乙炔脱氧尿苷 (EdU) 掺入确定 CD24 表达的区域含有活跃增殖的细胞,近端结肠中 EdU 标记细胞最常见于隐窝中部,而远端结肠中 EdU 标记细胞主要位于隐窝基底,两者之间存在明显差异。从小鼠结肠中通过上皮细胞黏附分子 (EpCAM) 阳性鉴定的单个上皮细胞的流式细胞分析显示,CD24(+) 部分包含大多数 Lgr5-EGFP(+) 假定的 CESC。定量 RT-PCR 的转录分析证实,CD24(+)EpCAM(+) 部分富含活跃的 CESC 标志物 [富含亮氨酸重复的 G 蛋白偶联受体 5 (Lgr5)、表皮生长因子受体 B2 (EphB2) 和 CD166],但也显示静止的 CESC 标志物 [富含亮氨酸重复和免疫球蛋白结构域 (Lrig)、双皮质素和钙调蛋白激酶样 1 (DCAMKL-1) 和鼠端粒酶逆转录酶 (mTert)] 的富集。我们得出结论,在野生型小鼠中基于 CD24 的分选分离了富含活跃循环和静止假定 CESC 的结肠上皮部分。此外,CD24 在正常结肠上皮中的表达可能对基于抗 CD24 的结直肠癌治疗具有重要意义。