YAP1 Regulates Breast Cancer Cell Mesenchymal-Like Stemness and Contributes to Trastuzumab Resistance Through Wnt/β-catenin Signaling Pathway

YE Xingming1, XU Yangmei¹, WU Xiufeng², LIU Qing¹, SU Lili¹, LIN Xiaowei¹, CHEN Li¹, HUANG Lijie¹, LIU Qinying¹*

(¹Fujian Provincial Key Laboratory of Tumor Biotherapy, NHC Key Laboratory of Cancer Metabolism, Clinical Oncology School ofFujian Medical University, Fujian Cancer Hospital, Fuzhou 350014, China; ²Department of Breast Surgical Oncology, Clinical Oncology School of Fujian Medical University, Fujian Cancer Hospital, Fuzhou 350014, China)

Abstract:

YAP1 has been reported to be involved in trastuzumab resistance through regulating EMT in gastric carcinoma. However, the role of mesenchymal-like stemness in the TR (trastuzumab-resistant) breast cancer is still elusive. Here, the function and mechanism of YAP1 related mesenchymal-like stemness in trastuzumab-resistant breast cancer were explored. TR breast cancer cell line was established. YAP1 plasmid (pcDNA3.1-YAP1) or YAP1 siRNAs were transfected into SKBr-3 (WT and TR) cells to overexpress or silence YAP1, respectively. The sensitivities of breast cancer cells to trastuzumab were detected by MTT assay. Proliferation was detected by clone formation. Invasiveness capability of cells was detected by Matrigel invasion assays. Stemness of cells was detected by tumor sphere formation. qRT-PCR (real-time fluorescence quantitative polymerase chain reaction) and Western blot were applied to detect mRNA and protein expression of YAP1, Ecadherin, Vimentin, CD44, Nanog, β-catenin and Cyclin D1. Compared with NC group, knockdown of YAP1 decreased the resistance of TR cells to trastuzumab (P<0.01), capacity of clone formation (P<0.01), invasiveness and sphere formation (P<0.01 and P<0.001). The expression of mesenchymal marker Vimentin and stem cell markers CD44 and Nanog was significantly down-regulated, whereas E-cadherin was significantly up-regulated (all P<0.05). Conversely, compared with NC group, overexpression of YAP1 increased the resistance of WT cells to trastuzumab (P<0.01), capacity of clone formation (P<0.001), invasiveness and sphere formation (all P<0.001). The expression of mesenchymal marker vimentin and stem cell marker CD44 and Nanog was significantly up-regulated, whereas E-cadherin was significantly down-regulated (all P<0.05). Furthermore, silencing of YAP1 reduced the expression of β-catenin, cyclin D1 and CD44 in TR cells (all P<0.01). These data indicated that YAP1 contributes to the mesenchymal-like stemness of breast cancer cell through Wnt/β-catenin signaling pathway; targeting YAP1 may inhibit trastuzumab resistance of BC. Furthermore, YAP1 leads to poor prognosis in HER2+ breast cancer patients.

CSTR: 32200.14.cjcb.2026.07.0007