甲状旁腺激素相关蛋白诱导 STAT5 激活、分泌分化并加速乳腺肿瘤的发展。

BACKGROUND: Parathyroid hormone-related protein (PTHrP) is required for embryonic breast development and has important functions during lactation, when it is produced by alveolar epithelial cells and secreted into the maternal circulation to mobilize skeletal calcium used for milk production. PTHrP is also produced by breast cancers, and GWAS studies suggest that it influences breast cancer risk. However, the exact functions of PTHrP in breast cancer biology remain unsettled. METHODS: We developed a tetracycline-regulated, MMTV (mouse mammary tumor virus)-driven model of PTHrP overexpression in mammary epithelial cells (Tet-PTHrP mice) and bred these mice with the MMTV-PyMT (polyoma middle tumor-antigen) breast cancer model to analyze the impact of PTHrP overexpression on normal mammary gland biology and in breast cancer progression. RESULTS: Overexpression of PTHrP in luminal epithelial cells caused alveolar hyperplasia and secretory differentiation of the mammary epithelium with milk production. This was accompanied by activation of Stat5 and increased expression of E74-like factor-5 (Elf5) as well as a delay in post-lactation involution. In MMTV-PyMT mice, overexpression of PTHrP (Tet-PTHrP;PyMT mice) shortened tumor latency and accelerated tumor growth, ultimately reducing overall survival. Tumors overproducing PTHrP also displayed increased expression of nuclear pSTAT5 and Elf5, increased expression of markers of secretory differentiation and milk constituents, and histologically resembled secretory carcinomas of the breast. Overexpression of PTHrP within cells isolated from tumors, but not PTHrP exogenously added to cell culture media, led to activation of STAT5 and milk protein gene expression. In addition, neither ablating the Type 1 PTH/PTHrP receptor (PTH1R) in epithelial cells nor treating Tet-PTHrP;PyMT mice with an anti-PTH1R antibody prevented secretory differentiation or altered tumor latency. These data suggest that PTHrP acts in a cell-autonomous, intracrine manner. Finally, expression of PTHrP in human breast cancers is associated with expression of genes involved in milk production and STAT5 signaling. CONCLUSIONS: Our study suggests that PTHrP promotes pathways leading to secretory differentiation and proliferation in both normal mammary epithelial cells and in breast tumor cells.

背景：甲状旁腺激素相关蛋白 (PTHrP) 是胚胎期乳腺发育所必需的，在哺乳期也具有重要功能，此时它由肺泡上皮细胞产生并分泌到母体循环中，动员用于产奶的骨骼钙。PTHrP 也由乳腺癌产生，GWAS 研究表明它会影响乳腺癌风险。然而，PTHrP 在乳腺癌生物学中的确切功能仍未确定。

方法：我们开发了一种四环素调控的、MMTV（鼠乳腺肿瘤病毒）驱动的乳腺上皮细胞中 PTHrP 过表达模型（Tet-PTHrP 小鼠），并将这些小鼠与 MMTV-PyMT（多瘤中肿瘤抗原）乳腺癌模型杂交，以分析 PTHrP 过表达对正常乳腺生物学和乳腺癌进展的影响。

结果：PTHrP 在腔上皮细胞中的过表达导致了乳腺上皮的腺泡增生和分泌分化，伴有乳汁产生。这伴随着 Stat5 的激活和 E74 样因子-5（Elf5）的表达增加，以及哺乳期后 involution 的延迟。在 MMTV-PyMT 小鼠中，PTHrP 的过表达（Tet-PTHrP;PyMT 小鼠）缩短了肿瘤潜伏期并加速了肿瘤生长，最终降低了整体存活率。过表达 PTHrP 的肿瘤还显示出核 pSTAT5 和 Elf5 的表达增加、分泌分化和乳汁成分标志物的表达增加，并且组织学上类似于乳腺分泌性癌。从肿瘤中分离的细胞内过表达 PTHrP，但不是将 PTHrP 外源性添加到细胞培养基中，导致 STAT5 的激活和乳蛋白基因的表达。此外，在乳腺上皮细胞中敲除 PTH1R（PTH1R）或用抗 PTH1R 抗体治疗 Tet-PTHrP;PyMT 小鼠均不能阻止分泌分化或改变肿瘤潜伏期。这些数据表明 PTHrP 以细胞自主的、胞内方式发挥作用。最后，人类乳腺癌中 PTHrP 的表达与参与乳汁生成和 STAT5 信号通路的基因的表达相关。

结论：我们的研究表明，PTHrP 促进了正常乳腺上皮细胞和乳腺癌细胞中分泌分化和增殖的途径。