Connexin 43 gap junction affects survival and drug resistance of multiple myeloma side population cells.

Drug resistance remains a major challenge for multiple myeloma (MM) treatment, and side population (SP) cells may play a key role in this resistance. The function of connexin 43 (Cx43)-mediated gap junction intercellular communication (GJ-IC) in MM cells is poorly understood. Bone marrow mesenchymal stem cells (BMSCs) from different sources were isolated and cultured. SP cells of MM cell line RPMI 8266 were separated by flow cytometry. Real-time reverse transcriptase-polymerase chain reaction and Western blot were used to detect Cx43 mRNA and protein expression in BMSCs, RPMI 8266 and SP cells from different sources. The effects of BMSCs from different sources on SP cell cycle, in vitro colony formation ability, stem cell-related gene expression and drug resistance, and the addition of 18α glycyrrhetinic acid (18αGA) as a pathway inhibitor were observed. Here, we demonstrate that MM cells expressed Cx43 and contained a high percentage of SP cells. We observed an increase in the survival and proliferative capacity of SP cells compared with RPMI 8226 cells, but treatment with 18αGA decreased SP cell survival and proliferation (all P<0.05). MM cells were sensitive to dexamethasone- and bortezomib-induced apoptosis; however, this sensitivity was significantly decreased when MM cells were co-cultured with BMSCs, and 18αGA partly recovered this cytotoxicity (all P<0.05). Collectively, our data suggest that GJ-IC between BMSCs and MM cells is one of the important regulatory mechanisms underlying MM cells survival, proliferation, and drug sensitivity.