Life Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720, USA.
Breast Cancer Res. 2009;11(5):R72. doi: 10.1186/bcr2408.
Expression of the A and B forms of progesterone receptor (PR) in an appropriate ratio is critical for mammary development. Mammary glands of PR-A transgenic mice, carrying an additional A form of PR as a transgene, exhibit morphological features associated with the development of mammary tumors. Our objective was to determine the roles of estrogen (E) and progesterone (P) in the genesis of mammary hyperplasias/preneoplasias in PR-A transgenics.
We subjected PR-A mice to hormonal treatments and analyzed mammary glands for the presence of hyperplasias and used BrdU incorporation to measure proliferation. Quantitative image analysis was carried out to compare levels of latency-associated peptide and transforming growth factor beta 1 (TGFbeta1) between PR-A and PR-B transgenics. Basement membrane disruption was examined by immunofluorescence and proteolytic activity by zymography.
The hyperplastic phenotype of PR-A transgenics is inhibited by ovariectomy, and is reversed by treatment with E + P. Studies using the antiestrogen ICI 182,780 or antiprogestins RU486 or ZK 98,299 show that the increase in proliferation requires signaling through E/estrogen receptor alpha but is not sufficient to give rise to hyperplasias, whereas signaling through P/PR has little impact on proliferation but is essential for the manifestation of hyperplasias. Increased proliferation is correlated with decreased TGFbeta1 activation in the PR-A transgenics. Analysis of basement membrane integrity showed loss of laminin-5, collagen III and collagen IV in mammary glands of PR-A mice, which is restored by ovariectomy. Examination of matrix metalloproteases (MMPs) showed that total levels of MMP-2 correlate with the steady-state levels of PR, and that areas of laminin-5 loss coincide with those of activation of MMP-2 in PR-A transgenics. Activation of MMP-2 is dependent on treatment with E and P in ovariectomized wild-type mice, but is achieved only by treatment with P in PR-A mice.
These data establish a link between hormonal response, proliferation, modulation of MMP activity and maintenance of basement membrane integrity that depend on a balance in the expression levels of PR-A and PR-B isoforms. Notably, concomitant increased proliferation, due to inhibition of TGFbeta1 activation, and loss of basement membrane integrity, via increased MMP-2 activity, appear to be prerequisites for the PR-A hyperplastic phenotype.
孕激素受体（PR）A 和 B 两种形式的表达比例对于乳腺发育至关重要。携带额外的 PR-A 转基因的 PR-A 转基因小鼠的乳腺表现出与乳腺肿瘤发展相关的形态特征。我们的目标是确定雌激素（E）和孕激素（P）在 PR-A 转基因小鼠乳腺增生/前肿瘤发生中的作用。
我们对 PR-A 小鼠进行激素处理，并分析乳腺增生情况，并用 BrdU 掺入法测量增殖。通过定量图像分析比较 PR-A 和 PR-B 转基因之间潜伏相关肽和转化生长因子β 1（TGFbeta1）的水平。通过免疫荧光法检测基底膜破坏，通过酶谱法检测蛋白水解活性。
PR-A 转基因的增生表型被卵巢切除术抑制，并被 E+P 治疗逆转。使用抗雌激素 ICI 182,780 或抗孕激素 RU486 或 ZK 98,299 的研究表明，增殖的增加需要通过 E/雌激素受体α信号传导，但不足以引起增生，而通过 P/PR 的信号传导对增殖影响不大，但对于增生的表现是必不可少的。增殖增加与 PR-A 转基因中 TGFbeta1 激活减少相关。基底膜完整性分析显示 PR-A 小鼠乳腺中层粘连蛋白-5、胶原 III 和胶原 IV 丢失，卵巢切除可恢复。基质金属蛋白酶（MMPs）的检查表明，MMP-2 的总水平与 PR 的稳态水平相关，并且在 PR-A 转基因中，层粘连蛋白-5 丢失的区域与 MMP-2 的激活区域相吻合。MMP-2 的激活依赖于去卵巢野生型小鼠中 E 和 P 的处理，但仅在 PR-A 小鼠中通过 P 的处理来实现。
这些数据建立了激素反应、增殖、MMP 活性调节和基底膜完整性维持之间的联系，这取决于 PR-A 和 PR-B 同工型表达水平的平衡。值得注意的是，由于 TGFbeta1 激活的抑制导致的增殖增加，以及通过增加的 MMP-2 活性导致的基底膜完整性丧失，似乎是 PR-A 增生表型的先决条件。
