Integrated functional genomics and tissue-resolved transcriptomics identify PARD6B as a context-dependent proliferative dependency in high-grade serous ovarian cancer

Introduction High-grade serous ovarian cancer (HGSOC) is characterized by profound genomic instability and tissue-level heterogeneity, complicating the translation of cell-line dependencies into patient-relevant vulnerabilities. Methods This study developed a function-first, tissue-resolved framework integrating DepMap CRISPR screening, four independent HGSOC single-cell RNA sequencing cohorts, paired malignant–microenvironment analyses within the same physical samples, spatial transcriptomics, normal fallopian-tube single-cell references, and experimental perturbation. Results Among 18,513 genes evaluable across 11 HGSOC models, 1,762 met prespecified recurrence criteria, and 58 remained after exclusion of common-essential and broadly dependent genes. par-6 family cell polarity regulator beta (PARD6B) was dependent in eight of 11 models, with a stable dependency phenotype across DepMap releases. Across 29 patients from four independent single-cell cohorts, PARD6B was recurrently detected in malignant cells. Within matched tissue samples, PARD6B was strongly enriched in malignant cells relative to fibroblast, endothelial, and immune compartments, whereas enrichment relative to mesothelial-like cells was modest and did not reach multiplicity-adjusted significance. Patient-level tissue analyses further supported malignant-compartment enrichment. Importantly, PARD6B remained readily detectable in normal fallopian-tube secretory and ciliated epithelium, indicating that its functional selectivity cannot be inferred from tumor-versus-normal expression alone. In KURAMOCHI and OVCAR-8 cells, two independent PARD6B-directed shRNAs suppressed short-term growth and clonogenic capacity, increased G1 representation and reduced S-phase entry, and produced a progressive competitive-fitness disadvantage, with stronger effects in KURAMOCHI cells. Conclusions Together, these findings identify PARD6B as a recurrent, context-dependent proliferative dependency in HGSOC and establish a function-first, tissue-resolved framework for distinguishing tumor-cell vulnerabilities from expression patterns across the tumor microenvironment and normal epithelium. Further studies are warranted to define the molecular determinants of PARD6B dependence and its therapeutic index.