Baicalin Attenuates YAP Activity to Suppress Ovarian Cancer Stemness

Yucong Li,1– 3 Dong Wang,1 Jingshu Liu,1 Yunzhe Li,1 Duke Chen,1 Lei Zhou,4 Tingyuan Lang,1– 3 Qi Zhou1– 3 1Department of Gynecologic Oncology, Chongqing University Cancer Hospital, Chongqing 400030, People’s Republic of China; 2Chongqing Key Laboratory of Translational Research for Cancer Metastasis and Individualized Treatment, Chongqing University Cancer Hospital, Chongqing 400030, People’s Republic of China; 3Key Laboratory for Biorheological Science and Technology of Ministry of Education (Chongqing University), Chongqing University Cancer Hospital, Chongqing 400044, People’s Republic of China; 4Singapore Eye Research Institute, Singapore, 169856, SingaporeCorrespondence: Qi Zhou; Tingyuan LangDepartment of Gynecologic Oncology, Chongqing University Cancer Hospital, Chongqing 400030, People’s Republic of ChinaTel +86 18908384529; +86 18717859346Fax +86 23 65311341Email cqzl_zq@163.com; michaellang2009@163.comPurpose: This study aims to reveal the mechanism underlying baicalin-suppressing ovarian cancer stemness.Methods: OVCAR-3 and the primary ovarian cancer cells were used for cell model. The ovarian cancer stem cells were isolated by suspension culture. Cell viability and clonogenicity were examined by CCK-8 assay and colony formation assay. The self-renewal of the cells was evaluated by the determination of sphere-forming capacity and the frequency of in vitro sphere-forming and in vivo tumor-initiating cells. The mRNA and protein levels were relatively quantified by qRT-PCR and Western blot. The transcription regulation of target genes was tested by luciferase reporter assay and a modified nuclear rn-on qRT-PCR assay.Results: Treatment with a non-toxic dose of baicalin significantly inhibited the spherogenicity of ovarian cancer cells. Moreover, a non-toxic dose of baicalin treatment suppressed the frequency of sphere-forming and tumor-initiating ovarian cancer cells. Furthermore, the expression of ovarian cancer stem cell markers (CD133 and ALDH1A1) was inhibited by a non-toxic dose of baicalin treatment. Baicalin inhibits YAP activity and suppresses RASSF6, a positive regulator of YAP, at the transcriptional level. Overexpression of both YAP and RASSF6 abolished the inhibitory effect of baicalin on the proliferation and stemness of ovarian cancer cells.Conclusion: The results in this study demonstrated that baicalin suppresses the stemness of ovarian cancer cells by attenuating YAP activity via inhibiting RASSF6 at the transcriptional level. This finding revealed baicalin as a novel YAP inhibitor that could serve as an anti-cancer drug for eradicating ovarian cancer stem cells.Keywords: baicalin, ovarian cancer, stemness, YAP, RASSF6