PRP-1 significantly decreases the ALDH(high) cancer stem cell population and regulates the aberrant Wnt/β-catenin pathway in human chondrosarcoma JJ012 cells

Chondrosarcomas are malignant bone tumors refractory to chemotherapy and radiation treatment; thus, novel therapeutic strategies are required. Proline-rich polypeptide 1 (PRP-1) has previously demonstrated antitumor properties in chondrosarcoma. To further investigate the role of PRP-1 in chondrosarcoma cells, its effects on cancer stem cell (CSC) populations were determined by analyzing aldehyde dehydrogenase (ALDH) activity, an established marker of CSCs, in association with regulation of the Wnt/β-catenin signaling. A significant decrease in ALDH(high) CSCs was observed following treatment of chondrosarcoma JJ012 cells with PRP-1. For RT(2) profiler PCR array analysis of Wnt/β-catenin signaling genes, cells were sorted into: i) Bulk JJ012 cells; ii) ALDH(high) cells sorted from untreated JJ012 cells (ALDH(high-untreated)); and iii) ALDH(low) cells sorted from PRP-1-treated JJ012 cells (ALDH(low-PRP-1)). The expression levels of Wnt/β-catenin signaling genes were determined to be downregulated in the ALDH(high-untreated) cells and upregulated in ALDH(low-PRP-1) cells when compared to the bulk JJ012 cells. Additionally, two important oncogenes involved in this pathway, MMP7 and CCND2, were found to be downregulated in the ALDH(low-PRP-1) cells. Immunocytochemistry demonstrated the localization of β-catenin in the nuclei of the PRP-1-treated cells. Western blotting indicated increased β-catenin expression in the ALDH(low-PRP-1) cells compared with the bulk JJ012 cells. Analysis of the cytoplasmic and nuclear fractions of cells treated with increasing concentrations of PRP-1 and β-catenin nuclear translocation inhibitor CGP57380, suggested the nuclear translocation of β-catenin following PRP-1 treatment. In addition, treatment of JJ012 cells with a specific ALDH inhibitor, diethylaminobenzaldehyde, and PRP-1 resulted in a significant decrease in cytoplasmic β-catenin protein expression. This indicated that ALDH inactivation may be associated with the nuclear translocation of β-catenin. Derivation of sarcomas from mesenchymal stem cells via inactivation of the Wnt pathway has been previously documented. The findings of the present study support the notion that Wnt/β-catenin activation may serve a differential role in sarcomas, limiting tumor progression in association with decreased CSC activity.