[Regulation of miRNA-15a/-16 expression on the drug resistance of myeloma cells]

To explore the effects and mechanism of bone marrow stromal cells (BMSCs) on the drug resistance of multiple myeloma (MM).

Fresh untreated MM patient (5 samples) and health donor (5 samples) bone marrow samples were collected from May 2011 to July 2011 at our hospital. Their BMSCs were separated respectively. The supernatant expression of cytokines in BMSCs was detected by enzyme-linked immunosorbent assay (ELISA). Myeloma cells were co-cultured with BMSCs and treated with melphalan or bortezomib. Cell proliferation and miRNA-15a/-16 expression of myeloma cells were measured in different culture conditions with thiazoyl blue tetrazolium bromide (MTT) assay and quantitative real-time PCR (qRT-PCR). miRNA-15a was transfected into myeloma cells. And the miRNA-15a functions on cell cycle and cell apoptosis were detected by flow cytometry.

ELISA assay showed that cytokine IL-6 and VEGF were at higher levels in MM-BMSCs than healthy BMSCs ((189 ± 9) vs (115 ± 15) pg/ml, (1497 ± 40) vs (1239 ± 21) pg/ml, both P < 0.05). The miRNA-15a/-16 expressions of myeloma cells were up-regulated after the treatment of melphalan and bortezomib (all P < 0.05). However, the miRNA-15a/-16 up-regulation by melphalan or bortezomib became inhibited when MM cells were co-cultured with MM-BMSCs (melphalan: 4.690 ± 0.050 vs 34.440 ± 4.100, 0.760 ± 0.070 vs 12.030 ± 1.020, bortezomib: 1.440 ± 0.230 vs 11.480 ± 1.488, 0.880 ± 0.040 vs 3.680 ± 0.420, all P < 0.05). Furthermore, IL-6 suppressed the expression of miRNA-15a/-16 in a dose and time-dependent pattern. The transfection of miRNA-15a led to the arrest of MM cell cycle in G(1)/S phase.

BMSCs suppress the proliferation of myeloma cells and regulate the drug sensitivity of myeloma cells through the inhibited expression of miRNA-15a/-16. IL-6 plays a pivotal role in the occurrence of drug resistance.