Department of Nutritional Sciences, The Pennsylvania State University, 222 Chandlee, University Park, PA 16802-6110, USA.
Exp Cell Res. 2010 Feb 1;316(3):366-75. doi: 10.1016/j.yexcr.2009.10.011. Epub 2009 Oct 21.
Breast cancer is associated with zinc (Zn) hyper-accumulation in breast tissue which is postulated to be potentiated by the over-expression of Zn importing proteins. Zip6 (LIV-1) over-expression has been documented in estrogen receptor-positive (ER+) breast tumors. Anti-estrogens, such as fulvestrant, are typically prescribed for ER+ breast cancer and thus may play a role in modulating cellular Zn hyper-accumulation. Herein, we investigated the physiological relevance of Zip6 over-expression and the consequences of Zip6-attenuation in breast tumor cells as a mechanism in the development of anti-estrogen resistance. We documented that over-expression of Zip6 was associated with significantly higher cellular Zn levels in tumor cells compared with normal breast cells. Fulvestrant significantly reduced Zn accumulation in tumor cells, without robust effects on Zip6 protein abundance. Zip6-attenuation significantly reduced cellular Zn pools, which was associated with increased mitochondrial membrane potential (DeltaPsim) and decreased apoptotic stimuli (cytoplasmic cytochrome C release, caspase-3 and -9 activities). Importantly, decreased apoptosis significantly increased tumor colony formation in soft agar and was associated with reduced E-cadherin expression. Our data suggest that anti-estrogen treatment regulates Zn level and importantly verify that Zip6 over-expression is not an underlying mechanism initiating breast cancer, but in fact may play a "tumor-constraining" role.
乳腺癌与乳腺组织中锌（Zn）的过度积累有关，据推测，这是由于 Zn 导入蛋白的过度表达所致。Zip6（LIV-1）在雌激素受体阳性（ER+）乳腺癌肿瘤中已有报道。抗雌激素药物，如氟维司群，通常用于治疗 ER+乳腺癌，因此可能在调节细胞 Zn 过度积累方面发挥作用。在此，我们研究了 Zip6 过度表达的生理相关性以及在乳腺癌细胞中 Zip6 衰减的后果，作为抗雌激素耐药性发展的一种机制。我们发现，与正常乳腺细胞相比，Zip6 过表达与肿瘤细胞中显著更高的细胞 Zn 水平相关。氟维司群显著减少了肿瘤细胞中的 Zn 积累，但对 Zip6 蛋白丰度没有明显影响。Zip6 衰减显著减少了细胞 Zn 池，这与线粒体膜电位（DeltaPsim）增加和凋亡刺激物减少（细胞质细胞色素 C 释放、半胱天冬酶-3 和 -9 活性）有关。重要的是，凋亡减少显著增加了软琼脂中的肿瘤集落形成，并与 E-钙黏蛋白表达减少有关。我们的数据表明，抗雌激素治疗调节 Zn 水平，重要的是验证了 Zip6 过表达不是引发乳腺癌的潜在机制，而是实际上可能发挥“肿瘤限制”作用。
