Sivasailam Aswathy, Kumar Kiran S, Jayaprasad Aparna Geetha, Jancy Shine Varghese, Harikumar Ashwathi, Unnikrishnan P S, Sivakumar K C, Tiffee P J Jain, Halikar Aman Munirpasha, Nithin S S, Pillai Prakash R, Tiwari Shivanshu Kumar, Sanjeev Vishnu S, Surabhi A V, Santhoshkumar T R
Cancer Research Program, BRIC-Rajiv Gandhi Centre for Biotechnology, Poojappura, Thycaud P.O., Thiruvananthapuram, Kerala, 695014, India.
Research Centre, University of Kerala, Thiruvananthapuram, India.
Biol Direct. 2025 Jun 13;20(1):70. doi: 10.1186/s13062-025-00653-8.
Breast cancer is subdivided into four distinct subtypes based on the status of hormone receptors (HR) and human epidermal growth factor receptor 2 (HER2) as HER2/HR, HER2/HR, HER2/HR and HER2/HR. Among this, ERα positive breast cancer, even though they respond to endocrine treatment, half of the patients acquire resistance and progress with metastasis despite ERα status. Spatio-temporal changes in ERα and their loss under treatment pressure have been reported in a subset of patients, which is a serious problem.
We have demonstrated that in vitro-generated resistance is correlated with the down regulation of ERα. To study the ERα status transition in live cells, triple-negative breast cancer cells were engineered to express EGFP-ERα, which further supported the existence of complex intracellular signaling that regulates ERα plasticity even in unperturbed conditions. Single-cell clones generate heterogeneity and loss of expression depending on proliferative cues. However, the initial response of cells to 4 μM of 4-hydroxytamoxifen and 1 μM of endoxifen involves up-regulation of ERα, likely due to its early effect on the proteasome or autophagy pathway. Supporting this, inhibition of autophagy and the proteasome further enhanced the expression of ERα. Systematic analysis of RNA sequencing of ERα stable cells further confirmed that ERα regulates diverse intracellular signaling networks such as ubiquitin, proteasome pathways, cell proliferation and Unfolded Protein Responses (UPR), implicating its direct role in post-translational protein modifications. Cell cycle indicator probe expressing receptor-positive breast cancer cells confirmed the ERα expression heterogeneity both in 2D and 3D culture in a cell cycle phase-independent manner.
Overall, the study confirms the cell's intrinsic post-transcriptional mechanisms of ERα plasticity that could play a role in receptor heterogeneity and tumor progression under endocrine treatment, which warrants further investigation.
乳腺癌根据激素受体（HR）和人表皮生长因子受体2（HER2）的状态分为四种不同亚型，即HER2⁺/HR⁺、HER2⁺/HR⁻、HER2⁻/HR⁺和HER2⁻/HR⁻。其中，雌激素受体α（ERα）阳性乳腺癌患者尽管对内分泌治疗有反应，但仍有一半患者会产生耐药并发生转移，尽管其ERα状态良好。已有报道称，部分患者存在ERα的时空变化及其在治疗压力下的丢失，这是一个严重问题。
我们已经证明，体外产生的耐药性与ERα的下调相关。为了研究活细胞中ERα状态的转变，我们对三阴性乳腺癌细胞进行基因改造，使其表达增强绿色荧光蛋白（EGFP）标记的ERα，这进一步证明了即使在未受干扰的条件下，也存在调节ERα可塑性的复杂细胞内信号传导。单细胞克隆会根据增殖信号产生异质性和表达缺失。然而，细胞对4 μM 4-羟基他莫昔芬和1 μM内昔芬的初始反应涉及ERα的上调，这可能是由于其对蛋白酶体或自噬途径的早期作用。支持这一观点的是，抑制自噬和蛋白酶体可进一步增强ERα的表达。对ERα稳定细胞的RNA测序进行系统分析进一步证实，ERα调节多种细胞内信号网络，如泛素、蛋白酶体途径、细胞增殖和未折叠蛋白反应（UPR），这表明其在翻译后蛋白质修饰中起直接作用。表达细胞周期指示剂探针的受体阳性乳腺癌细胞在二维和三维培养中均以细胞周期阶段无关的方式证实了ERα表达的异质性。
总体而言，该研究证实了ERα可塑性的细胞内转录后机制，这可能在内分泌治疗下的受体异质性和肿瘤进展中起作用，值得进一步研究。
