Institute for Research in Immunology and Cancer, Montréal, QC, H3C 3J7, Canada.
Department of Biochemistry and Molecular Medicine, Université de Montréal, Montréal, QC, H3C 3J7, Canada.
Oncogene. 2019 Feb;38(7):1019-1037. doi: 10.1038/s41388-018-0468-9. Epub 2018 Sep 6.
Antiestrogens (AEs) are widely used for treatment of estrogen receptor alpha (ERα)-positive breast cancer, but display variable degrees of partial agonism in estrogen target tissues and breast cancer (BC) cells. The fact that BC cells resistant to selective ER modulators (SERMs) like tamoxifen (Tam) can still be sensitive to pure AEs, also called selective ER downregulators, suggests different mechanisms of action, some of which may contribute to the more complete suppression of estrogen target genes by pure AEs. We report herein that pure AEs such as fulvestrant induce transient binding of ERα to DNA, followed by rapid release after 30-40 min without loss of nuclear localization. Loss of DNA binding preceded receptor degradation and was not prevented by proteasome inhibition. Chromatin was less accessible in the presence of fulvestrant than with estradiol or Tam as early as 20 min following treatment, suggesting that chromatin remodeling by pure AEs at ERα target regions prevents transcription in spite of receptor binding. SUMO2/3 marks were detected on chromatin at the peak of ERα binding in cells treated with pure AEs, but not SERMs. Furthermore, decreasing SUMOylation by overexpressing the deSUMOylase SENP1 significantly delayed receptor release from DNA and de-repressed expression of estrogen target genes in the presence of fulvestrant, both in ERα-expressing MCF-7 cells and in transiently transfected ER-negative SK-BR-3 cells. Finally, mutation V534E, identified in a breast metastasis resistant to hormonal therapies, prevented ERα modification and resulted in increased transcriptional activity of estrogen target genes in the presence of fulvestrant in SK-BR-3 cells. Together, our results establish a role for SUMOylation in achieving a more complete transcriptional shut-off of estrogen target genes by pure AEs vs. SERMs in BC cells.
抗雌激素（AEs）被广泛用于治疗雌激素受体 alpha（ERα）阳性乳腺癌，但在雌激素靶组织和乳腺癌（BC）细胞中显示出不同程度的部分激动作用。事实上，BC 细胞对选择性雌激素受体调节剂（SERMs）如他莫昔芬（Tam）的耐药性仍然对纯 AEs（也称为选择性 ER 下调剂）敏感，这表明了不同的作用机制，其中一些可能有助于纯 AEs 更完全地抑制雌激素靶基因。我们在此报告称，纯 AEs 如氟维司群会诱导 ERα 与 DNA 的短暂结合，然后在 30-40 分钟后迅速释放，而不会失去核定位。受体降解发生在 DNA 结合丢失之前，并且不会被蛋白酶体抑制所阻止。在存在氟维司群的情况下，染色质的可及性比用雌二醇或 Tam 处理时更早，即在处理后 20 分钟内降低，这表明纯 AEs 在 ERα 靶区的染色质重塑会阻止转录，尽管受体结合。在纯 AEs 处理的细胞中，SUMO2/3 标记在 ERα 结合的高峰期被检测到染色质上，但在 SERMs 中没有。此外，通过过表达去 SUMO 酶 SENP1 降低 SUMOylation 会显著延迟受体从 DNA 上的释放，并在氟维司群存在的情况下解除雌激素靶基因的表达抑制，这在表达 ERα 的 MCF-7 细胞和瞬时转染的 ER 阴性 SK-BR-3 细胞中都是如此。最后，在对激素治疗有抗药性的乳腺癌转移中发现的 V534E 突变，阻止了 ERα 的修饰，并导致在 SK-BR-3 细胞中氟维司群存在时雌激素靶基因的转录活性增加。总之，我们的结果确立了 SUMOylation 在纯 AEs 与 SERMs 相比，在 BC 细胞中实现雌激素靶基因更完全转录关闭中的作用。
