Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, Massachusetts, United States of America.
Department of Medicine, Harvard Medical School, Boston, Massachusetts, United States of America.
PLoS Genet. 2019 Mar 20;15(3):e1008002. doi: 10.1371/journal.pgen.1008002. eCollection 2019 Mar.
Mammary epithelial progenitors are the normal cell-of-origin of breast cancer. We previously defined a population of p27+ quiescent hormone-responsive progenitor cells in the normal human breast whose frequency associates with breast cancer risk. Here, we describe that deletion of the Cdkn1b gene encoding the p27 cyclin-dependent kinase inhibitor in the estrogen-induced mammary tumor-susceptible ACI rat strain leads to a decrease in the relative frequencies of Cd49b+ mammary luminal epithelial progenitors and pregnancy-related differentiation. We show by comprehensive gene expression profiling of purified progenitor and differentiated mammary epithelial cell populations that p27 deletion has the most pronounced effects on luminal progenitors. Cdkn1b-/- females have decreased fertility, but rats that are able to get pregnant had normal litter size and were able to nurse their pups implying that loss of p27 in ACI rats does not completely abrogate ovarian function and lactation. Reciprocal mammary gland transplantation experiments indicate that the p27-loss-induced changes in mammary epithelial cells are not only caused by alterations in their intrinsic properties, but are likely due to altered hormonal signaling triggered by the perturbed systemic endocrine environment observed in Cdkn1b-/- females. We also observed a decrease in the frequency of mammary epithelial cells positive for progesterone receptor (Pr) and FoxA1, known direct transcriptional targets of the estrogen receptor (Erα), and an increase in phospho-Stat5 positive cells commonly induced by prolactin (Prl). Characterization of genome-wide Pr chromatin binding revealed distinct binding patterns in mammary epithelial cells of Cdkn1b+/+ and Cdkn1b-/- females and enrichment in genes with known roles in Notch, ErbB, leptin, and Erα signaling and regulation of G1-S transition. Our data support a role for p27 in regulating the pool size of hormone-responsive luminal progenitors that could impact breast cancer risk.
乳腺上皮祖细胞是乳腺癌的正常细胞起源。我们之前定义了一个在正常人类乳腺中存在的 p27+ 静止激素反应祖细胞群体，其频率与乳腺癌风险相关。在这里，我们描述了在雌激素诱导的乳腺肿瘤易感 ACI 大鼠中，编码 p27 细胞周期蛋白依赖性激酶抑制剂的 Cdkn1b 基因缺失会导致 Cd49b+ 乳腺腔上皮祖细胞的相对频率降低，以及妊娠相关的分化。我们通过对纯化的祖细胞和分化的乳腺上皮细胞群体进行全面的基因表达谱分析表明，p27 缺失对腔前体细胞的影响最为显著。Cdkn1b-/- 雌性的生育能力下降，但能够怀孕的大鼠的产仔数正常，并且能够哺乳其幼崽，这表明 ACI 大鼠中 p27 的缺失并未完全阻断卵巢功能和泌乳。互惠性乳腺移植实验表明，p27 缺失诱导的乳腺上皮细胞变化不仅是由于其内在特性的改变，还可能是由于观察到的 Cdkn1b-/- 雌性中扰乱的系统性内分泌环境触发的激素信号改变所致。我们还观察到孕激素受体 (Pr) 和 FoxA1 阳性的乳腺上皮细胞频率降低，这是雌激素受体 (Erα) 的直接转录靶标，以及促乳素 (Prl) 通常诱导的磷酸化 Stat5 阳性细胞增加。全基因组 Pr 染色质结合的特征表明，Cdkn1b+/+ 和 Cdkn1b-/- 雌性乳腺上皮细胞的结合模式存在明显差异，并且在 Notch、ErbB、瘦素和 Erα 信号转导以及 G1-S 过渡调节中具有已知作用的基因中富集。我们的数据支持 p27 在调节激素反应性腔前体细胞池大小中的作用，这可能影响乳腺癌风险。
