MicroRNA Expression Analysis in Multiple Myeloma Plasma Cells and Cell Lines by a Quantitative Real-Time PCR Approach.

MicroRNAs (miRNAs) are small RNA molecules that negatively regulate gene expression at the post transcriptional level. Over the past few years, these miRNAs have been shown to be widely involved in diverse biological processes, like apoptosis, cell metabolism and cancer. The aim of this study was to compare the miRNA expression in multiple myeloma plasma cells to that in their normal counterparts. A subset of ten miRNAs was chosen based upon evidence in the literature for their role in tumorigenesis with special emphasis on B cell malignancies. The expression of mature miRNAs was examined with quantitative real-time reverse transcription based polymerase chain reaction (TaqMan®MicroRNA assay) in 7 human multiple myeloma (MM) cell lines, in purified bone marrow derived plasma cells from 4 MM patients, one MGUS patient and 3 healthy adults. The plasma cells from patients and controls were positively selected using CD138-coated microbeads. Our results showed that miR-15a and miR-21 were equally expressed in cell lines, patients and healthy controls. Therefore, these 2 miRNAs were used for normalization. All data were compared with the data derived from normal plasma cells. Higher expression was seen for let-7a, miR-16 and 2 members of the miR-17 cluster (miR-17-5p and miR-19b) both in MM patients and cell lines. Expression of miR-16 was much higher in the MM plasma cells than in the MGUS plasma cells (only one sample). The miR-181a showed a heterogeneous expression in cell lines but was normally expressed in patients. The miR-372 expression was below the level of accurate quantification in all samples. There was a dramatic difference between the stroma dependent (MM5.1) and the stroma independent cell line (MM5.2) in miR-155 expression. The miR-143 was less abundant in all cell lines and in one MM sample that contained more than 90% plasma cells. Interestingly, the MM5.2 cell line, which is stroma independent, reflecting a more aggressive MM stage, showed also a much lower expression for miR-143 than the stroma dependent counterpart (MM5.1). In summary, the results of this study show that there is a difference in miRNA expression between MM plasma cells and their healthy counterparts and also between more and less aggressive MM plasma cells, suggesting that miRNAs could play a role in disease onset and progression.