Juvenile myelomonocytic leukemia (JMML) is a rare disease of early childhood with a predilection for the monocyte/macrophage lineage. The pathogenesis of JMML is linked to dysregulated signal transduction through the NF1/RAS signaling pathway that is partially caused by genetic mutation of Ras, PTPN11, and c-CBL, or loss-of heterozygosity of Nf1. The hallmark of JMML is that JMML cells are selectively hypersensitive to GM-CSF in vitro. We previously reported that protein deficiencies of PTEN, CREB, and Egr-1 were frequently observed in JMML (67–87%). Recent research indicated that CREB was regulated by miR-34b, and Egr-1 was targeted by miR-183. We hypothesized that microRNAs may play an important role in contributing to the deficiency of these proteins. Using relative-quantitative real-time PCR, we evaluated the expression levels of miR-34b and miR-183 in mononuclear cells from 47 JMML patients. We found that the median level of miR-183 was significantly higher in JMML in comparison to normal controls (median=13.8 vs 4.2, p<0.001); but the median level of miR-34b was only slightly higher in JMML subjects, and not significantly so, compared to normal individuals (median=1.4 vs 1.0, p>0.05). This suggests that miR-34b does not play a significant role in JMML. Since extreme monocyte accumulation is one of the critical characteristics of JMML, we analyzed the correlation between the expression level of miR-183 and the monocyte percentage in the peripheral blood. Strikingly, there was a significant correlation between the expression level of miR-183 and the monocyte percentage in the peripheral blood from 34 patients who had available data (p<0.05). Based on a robust regression analysis, for every unit increase in the square root of RQ miR-183, the monocyte percentage significantly increased by 0.73% (SE=0.32%, p=0.023). This is the first evidence suggesting that microRNAs may contribute to the pathogenesis of JMML. miR-183 may also serve as an important biomarker that can be directly and quantitatively linked to significant clinical parameters in JMML. It also may ultimately provide a target for JMML therapy.
No relevant conflicts of interest to declare.
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