Program in Developmental Biology Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA.
Dev Biol. 2011 Apr 1;352(1):116-27. doi: 10.1016/j.ydbio.2011.01.025. Epub 2011 Jan 27.
The Hedgehog (Hh) signaling network is critical for patterning and organogenesis in mammals, and has been implicated in a variety of cancers. Smoothened (Smo), the gene encoding the principal signal transducer, is overexpressed frequently in breast cancer, and constitutive activation in MMTV-SmoM2 transgenic mice caused alterations in mammary gland morphology, increased proliferation, and changes in stem/progenitor cell number. Both in transgenic mice and in clinical specimens, proliferative cells did not usually express detectable Smo, suggesting the hypothesis that Smo functioned in a non-cell autonomous manner to stimulate proliferation. Here, we employed a genetically tagged mouse model carrying a Cre-recombinase-dependent conditional allele of constitutively active Smo (SmoM2) to test this hypothesis. MMTV-Cre- or adenoviral-Cre-mediated SmoM2 expression in the luminal epithelium, but not in the myoepithelium, was required for the hyper-proliferative phenotypes. High levels of proliferation were observed in cells adjacent or in close-proximity to Smo expressing cells demonstrating that SmoM2 expressing cells were stimulating proliferation via a paracrine or juxtacrine mechanism. In contrast, Smo expression altered luminal cell differentiation in a cell-autonomous manner. SmoM2 expressing cells, purified by fluorescence activated cell sorting (FACS) via the genetic fluorescent tag, expressed high levels of Ptch2, Gli1, Gli2, Jag2 and Dll-1, and lower levels of Notch4 and Hes6, in comparison to wildtype cells. These studies provide insight into the mechanism of Smo activation in the mammary gland and its possible roles in breast tumorigenesis. In addition, these results also have potential implications for the interpretation of proliferative phenotypes commonly observed in other organs as a consequence of hedgehog signaling activation.
刺猬（Hh）信号网络对于哺乳动物的模式形成和器官发生至关重要，并且与多种癌症有关。Smoothened（Smo），编码主要信号转导物的基因，在乳腺癌中经常过表达，而 MMTV-SmoM2 转基因小鼠中的组成型激活导致乳腺形态改变、增殖增加和干细胞/祖细胞数量变化。在转基因小鼠和临床标本中，增殖细胞通常不表达可检测到的 Smo，这表明 Smo 以非细胞自主方式发挥作用刺激增殖的假说。在这里，我们使用携带组成型激活 Smo（SmoM2）的 Cre 重组酶依赖性条件等位基因的遗传标记小鼠模型来检验这一假说。MMTV-Cre 或腺病毒-Cre 介导的 SmoM2 在腔上皮中的表达，但不在肌上皮中，是超增殖表型所必需的。在 Smo 表达细胞附近或紧邻 Smo 表达细胞的细胞中观察到高水平的增殖，表明 SmoM2 表达细胞通过旁分泌或旁分泌机制刺激增殖。相比之下，Smo 表达以细胞自主的方式改变腔上皮细胞的分化。通过遗传荧光标记通过荧光激活细胞分选（FACS）纯化的 SmoM2 表达细胞表达高水平的 Ptch2、Gli1、Gli2、Jag2 和 Dll-1，以及较低水平的 Notch4 和 Hes6，与野生型细胞相比。这些研究为 Smo 在乳腺中的激活机制及其在乳腺癌发生中的可能作用提供了深入了解。此外，这些结果还可能对解释 Hedgehog 信号激活后在其他器官中常见的增殖表型具有启示意义。
