Human cytomegalovirus reprograms breast cancer cells toward a triple-negative and metastatic phenotype

Abstract Breast cancer remains a leading cause of cancer-related mortality in women, with triple-negative breast cancer (TNBC) representing the most aggressive subtype due to the absence of effective targeted therapies. Human cytomegalovirus (HCMV) has increasingly been implicated in tumor progression; however, its mechanistic contribution to breast cancer pathogenesis remains poorly understood. Here, we investigated whether HCMV promotes TNBC-associated phenotypic reprogramming through modulation of key prognostic receptors and tumor-associated cellular pathways. Using transcriptomic, proteomic, molecular, and functional analyses in luminal (MCF7) and HER2-positive (SKBR3) breast cancer models, we demonstrate that HCMV infection induces extensive host-cell reprogramming characterized by suppression of ESR1, PGR, and ERBB2 expression at both transcript and protein levels, resulting in a receptor-suppressed state with selected TNBC-associated molecular features. Mechanistically, HCMV immediate-early (IE) proteins and the viral miRNAs hcmv-miR-US25-2-3p, hcmv-miR-UL36-3p, and hcmv-miR-UL22A-3p mediated repression of ESR1 and PGR. In contrast, ERBB2 downregulation occurred indirectly through virus-mediated suppression of the EGFR/CyclinD1/CDK4/6 axis, resulting in stabilization of the RB/E2F4 repressor complex at the ERBB2 promoter. Beyond receptor suppression, HCMV infection induced extensive inflammatory, metabolic, and epithelial-mesenchymal transition (EMT)-associated remodeling consistent with a state of virus-driven phenotypic plasticity. Although infected cells displayed reduced proliferative and metabolic activity, they exhibited enhanced invasion, EMT-associated transcriptional reprogramming, and increased metastatic dissemination in zebrafish xenograft models. Elevated TGFβ signaling and partial EMT-like states likely contributed to this invasive phenotype. Collectively, our findings identify multiple viral mechanisms through which HCMV promotes TNBC-associated cellular reprogramming and metastatic behavior. These results support a previously unrecognized role for HCMV in driving aggressive breast cancer phenotypes and highlight HCMV-targeted therapeutic strategies as potential approaches for HCMV-positive TNBC.