Restriction of YWHAB-mediated YAP cytoplasmic retention as a novel mechanism underlying stemness maintenance and chemo-resistance in peritoneal metastasis of ovarian cancer: A comparative proteomic study.

122 Background: Ovarian cancer (OC) peritoneal metastasis (OCPM) is a significant cause of high mortality of OC. To investigate the mechanisms underlying OCPM stemness maintenance and resistance, we characterized proteomic alterations in residual OCPM tissues after neoadjuvant chemotherapy (NACT), and verified restriction of YWHAB-mediated YAP cytoplasmic retention as a novel important mechanism. Methods: Tumor specimens from HGSOC patients underwent proteomic analysis using TMT and REACTOME for pathway and GO analysis. The OVCAR3 cell line, derived from malignant ascites, and formalin-fixed samples were used for Immunohistochemistry. Ovarian cancer stem-like cells, including cisplatin-resistant cells, were cultured, and ALHD activity was measured by qPCR and ALDEFLUOR Kit. Western blot and Co-IP were used for protein analysis. Sphere formation and limiting dilution assays were performed in vitro and in vivo using BALB/c nude mice, and FACS quantified OCSCs. YWHAB-knockdown cells were created via plasmids, lentivirus, and transfection. Statistical tests included paired and unpaired t-tests, one-way ANOVA, and ELDA for limiting dilution. Data are shown as mean ± SD, with *p< 0.05, **p< 0.01, ***p< 0.001 indicating significance. Results: TMT-based proteomics identified 324 differentially expressed proteins in post-NACT OCPM tissues, with 179 upregulated and 145 downregulated. Bioinformatics revealed novel targets in key pathways, including TUBB, VCP in Hedgehog, YWHAB in Hippo, TLA1/2, SPTA1 in MAPK, and FASN in NOTCH. YWHAB downregulation was confirmed in pPR OCPM tissues and cells, serving as a marker to differentiate pNR from pCR/pPR OCPM (AUC = 0.7673). YWHAB inhibition in pCR OCPM cells enhanced stemness, as seen in sphere formation, OCSC percentages, CD133 expression, ALDH activity, and tumorigenicity. It also induced cisplatin resistance. YWHAB inhibition reduced cytoplasmic YAP retention and increased nuclear YAP, enhancing transcriptional activity. YAP5SA expression negated the effects of YWHAB depletion on stemness and resistance in pCR OCPM cells. Conclusions: In summary, this study explored the potential mechanisms underlying OCPM stemness maintenance and resistance by employing proteomic analysis, and revealed a novel YWHAB-mediated mechanism. This finding indicates that YAP would an important target for eradicating YWHAB-restricted OCSCs in OCPM.