The Tisch Cancer Institute, Icahn School of Medicine at Mount Sinai, New York, NY 10029, USA.
Department of Pathology, New York University School of Medicine, New York, NY 10029, USA.
Cells. 2022 Mar 31;11(7):1179. doi: 10.3390/cells11071179.
Retinoids are essential in balancing proliferation, differentiation and apoptosis, and they exert their effects through retinoic acid receptors (RARs) and retinoid X receptors (RXRs). RARβ is a tumor-suppressor gene silenced by epigenetic mechanisms such as DNA methylation in breast, cervical and non-small cell lung cancers. An increased expression of RARβ has been associated with improved breast cancer-specific survival. The PAH2 domain of the scaffold protein SIN3A interacts with the specific in3 Interaction omain (SID) of several transcription factors, such as MAD1, bringing chromatin-modifying proteins such as histone deacetylases, and it targets chromatin for specific modifications. Previously, we have established that blocking the PAH2-mediated Sin3A interaction with SID-containing proteins using SID peptides or small molecule inhibitors (SMI) increased RARβ expression and induced retinoic acid metabolism in breast cancer cells, both in in vitro and in vivo models. Here, we report studies designed to understand the mechanistic basis of RARβ induction and function. Using human breast cancer cells transfected with MAD1 SID or treated with the MAD SID peptide, we observed a dissociation of MAD1, RARα and RARβ from Sin3A in a coimmunoprecipitation assay. This was associated with increased RARα and RARβ expression and function by a luciferase assay, which was enhanced by the addition of AM580, a specific RARα agonist; EMSA showed that MAD1 binds to E-Box, similar to MYC, on the RARβ promoter, which showed a reduced enrichment of Sin3A and HDAC1 by ChIP and was required for the AM580-enhanced RARβ activation in MAD1/SID cells. These data suggest that the Sin3A/HDAC1/2 complex co-operates with the classical repressors in regulating RARβ expression. These data suggest that SIN3A/MAD1 acts as a second RARβ repressor and may be involved in fine-tuning retinoid sensitivity.
类视黄醇在平衡增殖、分化和凋亡方面起着至关重要的作用，它们通过视黄酸受体（RARs）和视黄醛 X 受体（RXRs）发挥作用。RARβ 是一种肿瘤抑制基因，其表达受表观遗传机制如乳腺癌、宫颈癌和非小细胞肺癌中的 DNA 甲基化沉默。RARβ 的表达增加与改善乳腺癌特异性生存相关。支架蛋白 SIN3A 的 PAH2 结构域与 MAD1 等几种转录因子的特异性 in3 相互作用域（SID）相互作用，将组蛋白去乙酰化酶等染色质修饰蛋白募集到靶标，从而对特定的染色质进行修饰。以前，我们已经证实，使用含有 SID 的肽或小分子抑制剂（SMI）阻断 SIN3A 与含有 SID 的蛋白的 PAH2 介导的相互作用，可增加乳腺癌细胞中的 RARβ 表达并诱导视黄酸代谢，无论是在体外还是体内模型中。在这里，我们报告了旨在了解 RARβ 诱导和功能的机制基础的研究。使用转染 MAD1 SID 的人乳腺癌细胞或用 MAD SID 肽处理的细胞，我们在共免疫沉淀测定中观察到 MAD1、RARα 和 RARβ 从 Sin3A 中解离。这与通过荧光素酶测定观察到的 RARα 和 RARβ 表达和功能增强有关，该增强作用可通过添加特定的 RARα 激动剂 AM580 增强；EMSA 表明 MAD1 结合 RARβ 启动子上的 E-Box，类似于 MYC，ChIP 显示 Sin3A 和 HDAC1 的富集减少，并且需要 MAD1/SID 细胞中 AM580 增强的 RARβ 激活。这些数据表明，Sin3A/HDAC1/2 复合物与经典的抑制物共同调节 RARβ 表达。这些数据表明，SIN3A/MAD1 作为 RARβ 的第二个抑制因子发挥作用，可能参与精细调节视黄酸敏感性。
