Direct cell-cell interaction regulates division of stem cells from PC-3 human prostate cancer cell line

Cancer stem cells (CSCs) are a subpopulation that can drive recurrence and metastasis. Therefore, therapies targeting CSCs are required. Although previous findings have suggested that non-CSCs regulate the proliferation and differentiation of CSCs in the tumor microenvironment, the precise molecular mechanism is largely unknown. In this study, we found that a direct interaction between CSCs and non-CSCs downregulated CSC division in the PC-3 human prostate cancer cell line. We found that the proliferation of PC-3-derived CSCs (PrSCs) was significantly decreased (∼47%) in the presence of non-CSC-rich parental PC-3 cells compared with that in a culture in which they were absent. We observed no differences in PrSC proliferation when we indirectly cocultured them with PC-3 cells across a Transwell insert, and PrSCs that were transiently bound to immobilized PC-3 cells proliferated more slowly than those bound to PrSCs. The frequency of cell division with prior PrSC-PrSC contact was 2.8 times higher in the PrSC monoculture compared with that in the coculture with PC-3 cells. We found that the PrSCs were approximately 1.3 times more closely associated in the monoculture compared with the coculture with PC-3 cells, as determined by a cell proximity assay. The frequency of asymmetric PrSC division was 6.5% in the monoculture compared with 1.0% in the coculture with PC-3 cells (P < 0.045). By analyzing our data, we determined the importance of PrSC-non-CSC contact in regulating the frequency and mode of PrSC division. This regulation might be a valuable target for treating cancer.

Protease activated receptor 2 signaling promotes self-renewal and metastasis in colorectal cancer through β-catenin and periostin

The maintenance and expansion of cancer stem-like cells (CSCs) is necessary for metastasis. Although protease-activated receptor 2 (PAR2) is strongly associated with colorectal cancer (CRC) progression, it is unclear how it regulates distal metastasis, and no studies have shown the involvement of CSCs. In this study, we demonstrated that high PAR2 protein expression was correlated with metastatic CRC and poor prognosis in patients with stage III-IV CRC. CSCs from cell lines and patients showed higher levels of PAR2 than that of corresponding non-CSCs, and PAR2 inhibition reduced the CSC properties of the cell lines. Mechanistically, PAR2 inhibition switched the division mode of CSCs from symmetrical to asymmetrical via the ERK/GSK-3β/β-catenin pathway. We also identified periostin as a direct transcriptional target of β-catenin that mediates CSC self-renewal via PAR2 signaling. In a mouse xenograft model, PAR2 knockdown significantly attenuated liver metastasis. Finally, PAR2 expression was positively correlated with β-catenin and periostin in the primary sites of CRC with distant metastasis. Overall, our results indicate that PAR2 activation enhances CSC self-renewal and promotes metastasis through β-catenin and its target gene, periostin, in CRC.