Abstract
The aim of the present study was to investigate the expression level of microRNA 21 (miR‑21) in the peripheral blood of patients with multiple myeloma (MM) and to investigate the correlation between miR‑21 and sprouty homolog 2 (SPRY2) gene expression levels in MM. A total of 30 patients with MM, 15 with monoclonal gammopathy of undetermined significance (MGUS) and 20 normal control (NC) outpatients were selected for the detection of miR‑21 and SPRY2 expression using reverse transcription-quantitative polymerase chain reaction. In addition, western blot analysis was performed to detect the expression of miR‑21 and SPRY2 in MM cell lines. The expression of miR‑21 in U‑266 cells following lipofectamine transfection of fluorescence‑labeled miR‑21 mimic/inhibitor was observed using a fluorescence microscope and the expression level of SPRY2 in the miR‑21 mimic/inhibitor‑transfected U‑266 cells was detected using western blot analysis. The miR‑21 expression level in the circulating serum of the MM patient group was significantly higher (P<0.01) than that of the MGUS and NC groups. The MM cell lines with high endogenous miR‑21 expression exhibited an expression level of SPRY2 that was significantly lower than that in the MM cells with low endogenous miR‑21 expression. The transfection efficiency of fluorescence‑labeled miR‑21 mimic/inhibitor was >90%. Compared with the miR‑21 expression level in untreated U‑266 cells (0.82±0.13), the expression level of miR‑21 was increased by 120.2‑fold in miR‑21 mimic‑transfected cells (98.6±14.2; P<0.001) and was decreased by 61.9% in the miR‑21 inhibitor‑transfected cells (0.37±0.06; P<0.05). The grayscale value of protein bands demonstrated that SPRY2 protein expression significantly decreased in miR‑21 mimic‑transfected U‑266 cells compared with that in the inhibitor‑transfected, siRNA‑transfected and untreated cells (P<0.01). miR‑21 may represent a negative regulator involved in the downregulation of SPRY2 in MM. miR‑21 is closely associated with the pathogenesis, progression and prognosis of MM and may thus be used as an indicator of poor MM prognosis.