Cancer Biology Lab, Department of Gene Function and Regulation, Institute of Life Sciences, Chandrasekharpur, Bhubaneswar, India.
PLoS One. 2011;6(6):e20861. doi: 10.1371/journal.pone.0020861. Epub 2011 Jun 7.
Thyroid hormones regulate cell proliferation, differentiation as well as apoptosis. However molecular mechanism underlying apoptosis as a result of thyroid hormone signaling is poorly understood. The antiapoptotic role of Senescence Marker Protein-30 (SMP30) has been characterized in response to varieties of stimuli as well as in knock out model. Our earlier data suggest that thyroid hormone 3, 3'5 Triiodo L Thyronine (T(3)), represses SMP30 in rat liver.
METHODOLOGY/PRINCIPAL FINDINGS: In highly metastatic MCF-7, human breast cancer cell line T3 treatment repressed SMP30 expression leading to enhanced apoptosis. Analysis by flow cytometry and other techniques revealed that overexpression and silencing of SMP30 in MCF-7 resulted in decelerated and accelerated apoptosis respectively. In order to identify the cis-acting elements involved in this regulation, we have analyzed hormone responsiveness of transiently transfected hSMP30 promoter deletion reporter vectors in MCF-7 cells. As opposed to the expected epigenetic outcome, thyroid hormone down regulated hSMP30 promoter activity despite enhanced recruitment of acetylated H3 on thyroid response elements (TREs). From the stand point of established epigenetic concept we have categorised these two TREs as negative response elements. Our attempt of siRNA mediated silencing of TRβ, reduced the fold of repression of SMP30 gene expression. In presence of thyroid hormone, Trichostatin- A (TSA), which is a Histone deacetylase (HDAC) inhibitor further inhibited SMP30 promoter activity. The above findings are in support of categorisation of both the thyroid response element as negative response elements as usually TSA should have reversed the repressions.
This is the first report of novel mechanistic insights into the remarkable downregulation of SMP30 gene expression by thyroid hormone which in turn induces apoptosis in MCF-7 human breast cancer cells. We believe that our study represents a good ground for future effort to develop new therapeutic approaches to challenge the progression of breast cancer.
甲状腺激素调节细胞增殖、分化和凋亡。然而，甲状腺激素信号导致凋亡的分子机制还知之甚少。衰老标志物蛋白-30（SMP30）在应对各种刺激以及在敲除模型中的抗凋亡作用已经得到了描述。我们之前的数据表明，甲状腺激素 3,3'5 三碘甲状腺原氨酸（T3）抑制大鼠肝脏中的 SMP30。
方法/主要发现：在高度转移性 MCF-7 人乳腺癌细胞系中，T3 处理抑制 SMP30 的表达，导致细胞凋亡增加。通过流式细胞术和其他技术分析表明，在 MCF-7 中过表达和沉默 SMP30 分别导致细胞凋亡减慢和加速。为了确定参与这种调节的顺式作用元件，我们分析了瞬时转染 hSMP30 启动子缺失报告载体在 MCF-7 细胞中的激素反应。与预期的表观遗传结果相反，甲状腺激素下调 hSMP30 启动子活性，尽管甲状腺反应元件（TREs）上乙酰化 H3 的募集增加。从已建立的表观遗传概念的角度来看，我们将这两个 TRE 归类为负反应元件。我们用 siRNA 介导的 TRβ 沉默的尝试降低了 SMP30 基因表达的抑制倍数。在甲状腺激素存在的情况下，曲古抑菌素 A（TSA），一种组蛋白去乙酰化酶（HDAC）抑制剂，进一步抑制 SMP30 启动子活性。上述发现支持将两个甲状腺反应元件归类为负反应元件，因为通常 TSA 应该逆转抑制作用。
这是第一个关于甲状腺激素显著下调 SMP30 基因表达的新的机制见解的报告，这反过来又诱导 MCF-7 人乳腺癌细胞凋亡。我们相信，我们的研究为未来开发新的治疗方法来挑战乳腺癌的进展提供了一个很好的基础。
