Abstract 565: Establishing the mechanistic link between chemotherapy response and Hippo-YAP signaling in ovarian cancer.

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Abstract Ovarian cancer is one of the leading causes of cancer related deaths for women. First-line treatment includes surgical resection followed by a regimen of cisplatin. More than 70% of tumors, however, acquire chemoresistance. Our understanding of the molecular mechanisms mediating this resistance remains limited. Increased expression of YAP, a transcriptional co-factor inhibited by the Hippo pathway, correlates with poor prognosis, and is a biomarker of poor response to metal-based chemotherapies; yet the mechanistic link between chemotherapy treatment, regulation and changes of YAP driven transcription, and tumor cell response remains unclear. Using a combination of biochemistry, biophysics, and cell-based assays we sought to determine the molecular mechanism and consequences of cisplatin induced YAP activation in ovarian cancer. To determine whether and how cisplatin alters YAP activity in ovarian cancer, we monitored YAP localization, using immunofluorescence, and YAP target-gene transcription, using qPCR, in two ovarian cancer cell lines in the presence or absence of treatment. We find that cisplatin increased YAP nuclear localization and target gene transcription. To identify the step in Hippo signal transduction inhibited by cisplatin, we monitored known phosphorylation events in the Hippo core kinase cassette, via Western blot, in both ovarian cancer cells and in a recombinant system using purified proteins in the presence or absence of cisplatin. In both scenarios, we find that cisplatin prevented activation of the Hippo kinase LATS1/2 but did not alter the activity of the upstream Hippo kinase MST1/2. To determine the mechanism by which cisplatin inhibits LATS1/2, we monitored the solution behavior of LATS1 and its allosteric activator MOB1A; using mass photometry we find that the addition of cisplatin disrupts complex formation between LATS1 and MOB1A. Together, our data provides the first insights into the molecular mechanism by which cisplatin inhibits signal transduction in the Hippo pathway driving YAP activation in ovarian cancer. Future work aims to identify the YAP driven transcriptional changes that mediate chemoresistance to identify potential therapeutic strategies. Citation Format: Jonathan C. Vose, Elizabeth I. Harper, Sheetal Kooduvalli, Joanne Kotelawala, Ashani Weeraratna, Jennifer M. Kavran. Establishing the mechanistic link between chemotherapy response and Hippo-YAP signaling in ovarian cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 565.

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