Discoidin domain receptor 2 (DDR2) promotes breast cancer cell metastasis and the mechanism implicates epithelial-mesenchymal transition programme under hypoxia

Dasatinib and Doxorubicin Treatment of Sarcoma Initiating Cells: A Possible New Treatment Strategy

Background. One of the major challenges affecting sarcoma treatment outcome, particularly that of metastatic disease, is resistance to chemotherapy. Cancer-initiating cells are considered a major contributor to this resistance. Methods. An immortalised nontransformed human stromal (mesenchymal) stem cell line hMSC-TERT4 and a transformed cell line hMSC-TERT20-CE8, known to form sarcoma-like tumours when implanted in immune-deficient mice, were used as models. Receptor tyrosine kinase (RTK) activation was analysed by RTK arrays and cellular viability after tyrosine kinases inhibitor (TKI) treatment with or without doxorubicin was assessed by MTS assay. Results. Initial results showed that the hMSC-TERT4 was more doxorubicin-sensitive while hMSC-TERT20-CE8 was less doxorubicin-sensitive evidenced by monitoring cell viability in the presence of doxorubicin at different doses. The epidermal growth factor receptor (EGFR) was activated in both cell lines. However hMSC-TERT20-CE8 exhibited significantly higher expression of the EGFR ligands. EGFR inhibitors such as erlotinib and afatinib alone or in combination with doxorubicin failed to further decrease cell viability of hMSC-TERT20-CE8. However, inhibition with the TKI dasatinib in combination with doxorubicin decreased cell viability of the hMSC-TERT20-CE8 cell line. Conclusion. Our results demonstrate that dasatinib, but not EGFR-directed treatment, can decrease cell viability of stromal cancer stem cells less sensitive to doxorubicin.

Expression of beclin-1 in the microenvironment of invasive ductal carcinoma of the breast: correlation with prognosis and the cancer-stromal interaction

We examined the pathobiological properties of beclin-1, which is a key regulator of autophagosome formation in invasive ductal carcinoma of the breast, with a particular focus on the cancer microenvironment. Immunohistochemistry demonstrated that cancer cells and stromal mesenchymal cells expressed beclin-1 in 68 and 38 of 115 invasive ductal cancers, respectively. Expression of beclin-1 in cancer or stromal cells alone did not correlate with patient prognosis. In contrast, loss of beclin-1 in cancer cells and overexpression in stromal mesenchymal cells was associated with local cancer recurrence, postoperative lymph node metastasis, and a poor disease-free survival rate. A comprehensive gene expression analysis was performed on a co-culture of breast cancer cells and mesenchymal stromal cells, that latter of which either expressed beclin-1 or was depleted of beclin-1 by siRNA. Notably, siRNA-mediated downregulation of beclin-1 in mesenchymal cells co-cultured with breast cancer cells decreased the levels of various pro-inflammatory cytokines, their receptors, and collagen receptors. Quantitative reverse transcription polymerase chain reaction analysis confirmed that reduction of stromal beclin-1 expression decreased the expression of IL-1β and collagen receptor discoidin domain receptor 2 (DDR2). Microenvironmental IL-1β is believed to play an important role in tumor invasion. Recent work has also indicated that overexpression of DDR2 contributes to breast cancer invasion and lymph node metastasis. Taken together, these findings indicate beclin-1 expression in the stroma might be important for shaping the breast cancer microenvironment and thus could be a potent molecular target in patients with invasive ductal carcinoma of the breast.

DDR2 inhibition reduces migration and invasion of murine metastatic melanoma cells by suppressing MMP2/9 expression through ERK/NF-κB pathway

Metastatic melanoma is one of the most deadly and evasive cancers. Collagen I in the extracellular matrix promotes the migration and invasion of tumor cells through the production of matrix metalloproteinase (MMP) 2 and 9. Discoidin domain receptor (DDR) 2 is a collagen receptor that is implicated in several cancer types including breast and prostate cancers. However, the role of DDR2 in the migration and invasion of murine melanoma cells is less studied. In the present study, we investigated the effects and underlying mechanisms of DDR2 in migration and invasion of B16BL6 melanoma cells in response to collagen I. Results demonstrated that DDR2 is expressed and is phosphorylated by collagen I in the cells. Upon down-regulation of DDR2 using small-interfering RNA (siRNA) approach, both of the cell migratory and invasive phenotypes were significantly attenuated when compared with the control cells. This effect was mediated via suppression of MMP2/9 upon DDR2 inhibition. Furthermore, inhibition of DDR2 by specific siRNA markedly reduced the activation of extracellular regulated kinase (ERK) 1 and 2 and nuclear factor of kappa B (NF-κB) in the cells when compared with the control cells. Overall, these data demonstrated that DDR2 siRNA-mediated suppression of ERK1/2 and NF-κB could down-regulate the expressions of MMP2/9 in response to collagen I to reduce the migratory and invasive phenotypes of the cells.

Investigating microenvironmental regulation of human chordoma cell behaviour

The tumour microenvironment is complex and composed of many different constituents, including matricellular proteins such as connective tissue growth factor (CCN2), and is characterized by gradients in oxygen levels. In various cancers, hypoxia and CCN2 promote stem and progenitor cell properties, and regulate the proliferation, migration and phenotype of cancer cells. Our study was aimed at investigating the effects of hypoxia and CCN2 on chordoma cells, using the human U-CH1 cell line. We demonstrate that under basal conditions, U-CH1 cells express multiple CCN family members including CCN1, CCN2, CCN3 and CCN5. Culture of U-CH1 cells in either hypoxia or in the presence of recombinant CCN2 peptide promoted progenitor cell-like characteristics specific to the notochordal tissue of origin. Specifically, hypoxia induced the most robust increase in progenitor-like characteristics in U-CH1 cells, including increased expression of the notochord-associated markers T, CD24, FOXA1, ACAN and CA12, increased cell growth and tumour-sphere formation, and a decrease in the percentage of vacuolated cells present in the heterogeneous population. Interestingly, the effects of recombinant CCN2 peptide on U-CH1 cells were more pronounced under normoxia than hypoxia, promoting increased expression of CCN1, CCN2, CCN3 and CCN5, the notochord-associated markers SOX5, SOX6, T, CD24, and FOXA1 as well as increased tumour-sphere formation. Overall, this study highlights the importance of multiple factors within the tumour microenvironment and how hypoxia and CCN2 may regulate human chordoma cell behaviour.