Dissecting Context-Specific Effects of ERK5 Signaling in Triple-Negative Breast Cancer

<b>Background:</b> Triple-negative breast cancer (TNBC) is an aggressive subtype of cancer with poor clinical outcomes. There is a critical need to identify novel, druggable targets for TNBC to improve therapy response and patient outcomes. Due to their roles in critical processes driving cancer progression, kinases have been a major focus of drug discovery efforts. The role of extracellular signal-regulated kinase 5 (ERK5) in mediating TNBC extracellular matrix (ECM) has previously been described in 2D culture and in vivo. Here, we characterized the impact of ERK5 on breast cancer biology in 2D culture, 3D spheroids, and our 3D breast adipose-macrophysiological system (BA-MaPS). <b>Methods:</b> We assessed migration changes in MDA-MB-231 parental and ERK5-knockout (ERK5-ko) cells cultured in the three in vitro models using transwell, scratch, and spheroid pseudo-migration assays. Differential gene expression among these cell lines in the three platforms was assessed by RNA sequencing and pathway analysis. Stromal remodeling of adipocytes and matrix was evaluated by H&E and Masson's Trichrome. <b>Results:</b> Across the in vitro models, ERK5 deletion impaired TNBC cell migration. ERK5-mediated transcriptomic changes included genes associated with epithelial-to-mesenchymal transition (EMT) and migration, with further analysis showing significant alterations in core and associated matrisome. Histological staining corroborated the downregulation of collagen with ERK5 depletion in the BA-MaPS. The NFκB pathway was significantly upregulated only in the ERK5-ko 2D-cultured cells, not in 3D spheroids nor the BA-MaPS model. <b>Conclusions:</b> These results indicate a link between ERK5 and TNBC progression through regulation of TME remodeling, EMT, and cell motility. Differences in 2D culture, 3D spheroid, and BA-MaPS underscore the importance of using physiologically relevant models in breast cancer research.