Ko Young Shin, Won Ju Yeong, Jin Hana, Nguyen Nam Binh, Won Yaeram, Nsanzimana Vedaste, Yun Seung Pil, Park Sang Won, Kim Hye Jung
Department of Pharmacology, College of Medicine, Institute of Medical Sciences, Gyeongsang National University, Jinju, Gyeongsangnam‑do 52727, Republic of Korea.
Int J Mol Med. 2025 May;55(5). doi: 10.3892/ijmm.2025.5521. Epub 2025 Mar 21.
Expression levels of ATP‑binding cassette (ABC) transporters are known to be increased in various tumor cells, including in breast cancer, and they are responsible for mediating drug resistance, leading to treatment failure. In the present study, gene expression array analysis revealed that among ABC transporter subtypes, ABC subfamily G member 8 (ABCG8) was one of the most increased in radiotherapy‑resistant triple‑negative breast cancer (RT‑R‑TNBC) cells compared with in TNBC cells. ABCG8 is involved in sterol efflux; however, its role in cancer is not well known. Therefore, the present study investigated the effect of ABCG8 on tumor progression in RT‑R‑TNBC cells. Gene expression profiling was conducted using the QuantiSeq 3' mRNA‑Seq Service, followed by western blotting to confirm protein levels. Loss‑of‑function assays using small interfering RNA (si) transfection were performed to assess the roles of ABCG8 and its regulatory signaling pathways. RT‑R‑MDA‑MB‑231 cells exhibited increased cholesterol levels in both cells and the surrounding media via induction of sterol regulatory element binding protein 1 (mature form) and fatty acid synthase. siABCG8 transfection increased intracellular cholesterol levels but decreased cholesterol levels in the media, indicating an accumulation of cholesterol inside cells. Additionally, RT‑R‑MDA‑MB‑231 cells exhibited increased levels of β‑catenin compared with MDA‑MB‑231 cells, which was significantly reduced by ABCG8 knockdown. Furthermore, ABCG8 knockdown led to cell cycle arrest in the G2/M phase in RT‑R‑MDA‑MB‑231 cells by reducing Polo‑like kinase 1 (PLK1) and Cyclin B1 expression. RT‑R‑MDA‑MB‑231 cells also exhibited increased phosphorylated‑low‑density lipoprotein (LDL) receptor‑related protein 6 (LRP6) levels compared with MDA‑MB‑231 cells, and these were decreased by siABCG8 transfection. LRP6 siRNA transfection decreased β‑catenin, PLK1 and Cyclin B1 expression. In addition, feedback mechanisms such as liver X receptor and inducible degrader of LDL were decreased in RT‑R‑MDA‑MB‑231 cells under normal conditions compared with in MDA‑MB‑231 cells. To the best of our knowledge, the present study was the first to suggest that the cholesterol exported by ABCG8, not inside the cells, may affect cancer progression via the LRP6/Wnt/β‑catenin signaling pathway in RT‑R‑TNBC. The regulation of this pathway may offer a potential therapeutic strategy for the treatment of RT‑R‑TNBC.
已知三磷酸腺苷结合盒（ABC）转运蛋白在包括乳腺癌在内的各种肿瘤细胞中的表达水平会升高，它们负责介导耐药性，导致治疗失败。在本研究中，基因表达阵列分析显示，在ABC转运蛋白亚型中，与三阴乳腺癌（TNBC）细胞相比，ABC亚家族G成员8（ABCG8）在放疗抵抗性三阴乳腺癌（RT-R-TNBC）细胞中是表达增加最多的亚型之一。ABCG8参与固醇流出；然而，其在癌症中的作用尚不清楚。因此，本研究调查了ABCG8对RT-R-TNBC细胞肿瘤进展的影响。使用QuantiSeq 3' mRNA-Seq服务进行基因表达谱分析，随后进行蛋白质印迹以确认蛋白质水平。使用小干扰RNA（si）转染进行功能丧失分析，以评估ABCG8及其调节信号通路的作用。RT-R-MDA-MB-231细胞通过诱导固醇调节元件结合蛋白1（成熟形式）和脂肪酸合酶，使细胞内和周围培养基中的胆固醇水平升高。siABCG8转染增加了细胞内胆固醇水平，但降低了培养基中的胆固醇水平，表明胆固醇在细胞内积累。此外，与MDA-MB-231细胞相比，RT-R-MDA-MB-231细胞中β-连环蛋白水平升高，ABCG8敲低可显著降低该水平。此外，ABCG8敲低通过降低Polo样激酶1（PLK1）和细胞周期蛋白B1的表达，导致RT-R-MDA-MB-231细胞在G2/M期发生细胞周期阻滞。与MDA-MB-231细胞相比，RT-R-MDA-MB-231细胞中磷酸化低密度脂蛋白（LDL）受体相关蛋白6（LRP6）水平也升高，siABCG8转染可降低这些水平。LRP6 siRNA转染降低了β-连环蛋白、PLK1和细胞周期蛋白B1的表达。此外，与MDA-MB-231细胞相比，在正常条件下，RT-R-MDA-MB-231细胞中肝X受体和LDL诱导降解物等反馈机制减少。据我们所知，本研究首次表明，ABCG8输出而非细胞内的胆固醇可能通过LRP6/ Wnt/β-连环蛋白信号通路影响RT-R-TNBC的癌症进展。该信号通路的调节可能为RT-R-TNBC的治疗提供一种潜在的治疗策略。
