A novel c-Kit/phospho-prohibitin axis enhances ovarian cancer stemness and chemoresistance via Notch3-PBX1 and β-catenin-ABCG2 signaling.

BACKGROUND

The underlying mechanism involved in ovarian cancer stemness and chemoresistance remains largely unknown. Here, we explored whether the regulation of c-Kit and plasma membrane prohibitin (PHB) affects ovarian cancer stemness and chemotherapy resistance.

METHODS

Mass spectrum analysis and an in vitro kinase assay were conducted to examine the phosphorylation of PHB at tyrosine 259 by c-Kit. The in vitro effects of c-Kit on membrane raft-PHB in ovarian cancer were determined using tissue microarray (TMA)-based immunofluorescence, western blotting, immunoprecipitation, colony and spheroid formation, cell migration and cell viability assays. In vivo tumor initiation and carboplatin treatment were conducted in nude mice.

RESULTS

We found that c-Kit and PHB colocalized in the raft domain and were positively correlated in human ovarian serous carcinoma. c-Kit interacted with PHB and facilitated the phosphorylation of PHB at tyrosine 259 (phospho-PHB) in the membrane raft to enhance ovarian cancer cell motility. The generation of SKOV3GL-G4, a metastatic phenotype of SKOV3 green fluorescent protein and luciferase (GL) ovarian cancer cells, in xenograft murine ascites showed a correlation between metastatic potential and stem cell characteristics, as indicated by the expression of c-Kit, Notch3, Oct4, Nanog and SOX2. Further study revealed that after activation by c-Kit, raft-phospho-PHB interacted with Notch3 to stabilize Notch3 and increase the downstream target PBX1. Downregulation of raft-phospho-PHB increased the protein degradation of Notch3 through a lysosomal pathway and inhibited the β-catenin-ABCG2 signaling pathway. Moreover, raft-phospho-PHB played an important role in ovarian cancer stemness and tumorigenicity as well as resistance to platinum drug treatment in vitro and in vivo.

CONCLUSIONS

These findings thus reveal a hitherto unreported interrelationship between c-Kit and PHB as well as the effects of raft-phospho-PHB on ovarian cancer stemness and tumorigenicity mediated by the Notch3 and β-catenin signaling pathways. Targeting the c-Kit/raft-phospho-PHB axis may provide a new therapeutic strategy for treating patients with ovarian cancer.