Identification of driver genes/proteins in EOC tumorigenic processes is critical to increase the cure rate for late stage epithelial ovarian cancer (EOC), which has not been in improved over several decades. We have developed a highly aggressive EOC cell line (ID8-P1 or P1) from ID8-P0 (without in vivo passage, or P0) through in vivo passage in

C57BL6 mice. Two genes encode important desmosome components, desmoplakin (Dsp) and plakophilin 1 (Pkp1) were found to be significantly over-expressed in P1

vs. P0 cells, as well as human EOC cells. DSP is an obligate component of functional desmosomes that anchors intermediate filaments to desmosomal plaques. Pkp1 encodes a member of the arm-repeat (armadillo) and plakophilin (PKP) gene families. Our understanding of the functions of desmosomes in cancer is just emerging and the role of desmosomes in EOC is totally unknown. Our data showed the novel functions of DSP in anoikis-resistance and SRC activation using shRNA-mediated DSP-knocked down (KD) stable cell lines. In addition, we found that ID8-P1 cells formed spheroids and P0 cells tended to be single cells when they were cultured in suspension. KD-Dsp dissociated spheroids, suggesting that desmosomes play an important role in spheroid formation, which may be directly related to anoikis-, drug-resistance, and/or the cancer stem cell (CSC) concepts. Moreover, we found that enhanced glycolysis was involved in the increased anoikis-resistance of ID8-P1 cells and an inhibitor of glycolysis, shikonin (SHK) was a potent anoikis-resistance inhibitor and P1 cells gained more drug-resistance, when compared to P0 cells, with the IC50s were 1.7 and 7.4 μM for P0 and

P1 cells, respectively. Similarly, the IC50s were 2.4 and 8.1 μM for human EOC PE01 and PE04 cells, respectively. PE01 and PE04 cell lines are identified to represent high-grade serous ovarian cancer (HGSC), which were derived from the same patient before (PE01) and after (PE04) the onset of drug resistance to cis-platinum (CDDP), chlorambucil, and 5-fluorouracil. PP2 (a SRC nhibitor) and SHK were able to dissociate the cell-cells aggregates/spheroids in EOC cells. The previously unknown role of DSP and/or PKP1 in EOC may be related to their signaling activities outside desmosomes. Cells staining of PKP1 protein showed its cytosolic and perinuclear location, providing supporting and proof-of-concept data. Together, our data have suggested the novel links among DSP, PKP1, anoikis-resistance, SRC activation, cell-cell-aggregation, and

drug-resistance. These data provide a basis for developing new modalities for EOC treatment.

Citation Format: Yan Xu, Qingchun Cai. Role and signaling of desmosomal DSP and PKP1 in ovarian cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 5054.