Bone Marrow-Derived Mesenchymal Stem Cells Promote Growth and Migration of Osteosarcoma and Hepatocarcinoma Cells through CXCR4 and AQP1

Increasing evidences suggest that bone marrow-derived mesenchymal stem cells (BM-MSCs) are recruited into the stroma of developing tumors where they contribute to progression by enhancing tumor growth and metastasis, or by inducing anticancer-drug resistance. Although many experimental evidences exist supporting the therapeutic potential of MSCs, the mechanism of homing and recruitment of MSCs into tumors and their potential role in malignant tissue progression is still not well understood. The aim of this study was to elucidate the role of BM-MSCs to promote tumor cell proliferation and invasion. Therefore, we analyzed whether chemokine receptor type 4 (CXCR4) and water channel molecule, aquaporin 1 (AQP1), both known to play a key role in cancer metastases, could affect MSCs mediated osteosarcoma and hepacarcinoma progression. We used human mesenchymal stem cell isolated from bone marrow aspirates by gradient centrifugation and seeded in standard cell culture conditions. MSCs were grown for 48 h in medium with 1% fetal bovine serum to obtain conditioned medium (MSCs-CM) that was collected, filtered and stored at -20 °C. CXCR4 and AQP1 protein level was evaluated in human hepatocarcinoma (SNU-398) and osteosarcoma (U2OS) cells exposed to MSCs-CM. Proliferation of tumor cells co-cultured with MSCs or cultured in presence of MSCs-CM was evaluated by MTT assay. Tumor migration and invasion were assayed in 24-well transwell chambers using 8 um pore membrane precoated with collagen/fibronectin or matrigel, respectively. SNU-398 and U2OS cells, suspended in serum-free medium, were added to the upper chamber and incubated for 24-48 h at 37 °C in presence of MSCs-CM or MSCs (lower chamber) used as chemoattractants. Tumor cells pre-treated with a CXCR4 antagonist (AMD3100) or AQP1 antibody were also analyzed for proliferation, migration and invasion. Furthermore, involvement of Akt and/or Erk signalling pathways in tumor progression MSCs-mediated was examined. Our results showed that CXCR4 and AQP1 expression is increased in human hepatocarcinoma (SNU-398) and osteosarcoma (U2OS) cells in presence of MSCs secreted factors. Conditioned medium from MSCs promoted proliferation, migration and invasion of tumor cells, whereas inhibition of CXCR4 and AQP1 significantly down-regulated these effects. Furthermore, SNU-398 and U2OS cells showed an enhancement of p-Akt and p-Erk levels when they were cultured in presence of MSCs-CM. In conclusion these findings suggest that bone-marrow derived mesenchymal stem cells can promote the proliferation and invasion of osteosarcoma and hepatocarcinoma cells through CXCR4 and AQP1 overexpression. In addition, we found that MSCs may contribute to tumor progression by PI3K/Akt pathway and/or Ras/Erk cascade.