Bone marrow stromal cells protect myeloma cells from bortezomib induced apoptosis by suppressing microRNA-15a expression.

Despite unsurpassed anti-tumor activity of bortezomib for multiple myeloma (MM), drug resistance has emerged as a challenge, especially when MM cells adhere to the stroma. This study aimed to determine whether bone marrow stromal cells (BMSCs) have a role in the development of chemoresistance in MM. Our data demonstrate that the secretion of interleukin-6 (IL-6), vascular endothelial growth factor (VEGF), and cell-to-cell contact with microenvironment-derived stromal cells from patients with multiple myeloma (MM-BMSCs) significantly decreased the sensitivity of myeloma cells to bortezomib treatment. Mechanistically, we found that microRNA (miRNA)- 15a expression was up-regulated in U266 and NCI-H929 cells treated by bortezomib, which was inhibited by MM-BMSCs. miRNA-15a transfected myeloma cells were arrested in G1/S checkpoint and secreted less VEGF compared to control transfected cells, although no significant difference was found in VEGF mRNA levels. In conclusion, our data suggest that via suppressing miRNA-15a expression, BMSCs provide survival support and protect myeloma cells from bortezomib induced apoptosis.