Synthetic biological tuning of metastasis regulator reveals nonmonotonic phenotype response*

Dysregulation of transcription factor (TF) networks is a major pathogenic event in metastasis - one of the leading factors associated with high mortality of cancer. Although many qualitative relationships between oncogenic regulators and cancer phenotypes are known, their quantitative characterization and understanding is lacking. We established a synthetic biological framework to enable such quantitative characterization, and applied it to BACH1, a metastasis regulator. Upon establishing and characterizing BACH1 control in stable monoclonal in triple-negative breast cancer cell lines, we uncovered a non-monotonic relationship between BACH1 expression and cell invasion ability. We confirmed and characterized this non-monotonic landscape by analyzing BACH1 expression histograms of the invaded population at critical induction levels. A single-cell-level model explained the observed histogram shifts. Overall, we propose a systematic approach to quantify dose-dependent relationships between TFs and their phenotypic/regulatory functions in mammalian cells, with relevance to cancer, tissue homeostasis and development.