A Nutrient-Sensitive ZRF1-Dependent Secretory Network Involving S100A9 Contributes to Neutrophil Plasticity in Triple-Negative Breast Cancer.

Zuotin-related factor 1 (ZRF1) is an essential chromatin-associated regulator with established roles in transcription, differentiation, and cancer; however, its contribution to paracrine signaling within the tumor microenvironment (TME) remains unexplored. Here, we identify ZRF1 as a regulator of nutrient-sensitive tumor-derived paracrine signaling in triple-negative breast cancer (TNBC). Across multiple breast cancer subtypes, ZRF1 depletion altered the expression, secretion, and stress-associated protein patterns of the inflammatory mediator S100A9. This regulation was influenced by metabolic status, where nutrient deprivation selectively destabilized specific S100A9 proteoforms through proteasome-sensitive mechanisms. Bioinformatic analyses revealed a strong association between S100A9 expression and neutrophil infiltration in breast tumors, prompting functional investigation of ZRF1-mediated tumor-neutrophil communication using a multilayered experimental framework. Conditioned medium from ZRF1-deficient tumor cells induced a nonbinary neutrophil activation spectrum rather than a fixed polarization state. This phenotypic remodeling was characterized by altered inflammatory signaling and cytokine (IL-8) dynamics in both differentiated HL-60 neutrophil-like cells and primary human neutrophils. Functionally, ZRF1-dependent paracrine cues regulated neutrophil transendothelial migration over time. Reciprocal coculture platforms and real-time xCELLigence assays further demonstrated that ZRF1 loss sensitizes tumor cells to neutrophil-derived signals, enhancing invasion and driving state-dependent architectural remodeling in 3D tumor spheroids. Collectively, these findings support a model in which a nutrient-sensitive ZRF1-dependent secretory network involving S100A9 contributes to human neutrophil plasticity under metabolic stress. Consequently, this study highlights S100A9 as one component of a broader ZRF1-regulated secretory network and identifies nutrient-sensitive tumor-immune communication as a potential therapeutic vulnerability in aggressive breast cancer.