Decreased expression of microRNA-122 is associated with an unfavorable prognosis in childhood acute myeloid leukemia and function analysis indicates a therapeutic potential.

MicroRNA (miR)-122 functions as a tumor suppressor in various human cancers. However, its involvement in childhood acute myeloid leukemia (AML) remains unknown. In this study, quantitative real-time PCR assay demonstrated that miR-122 expression in bone marrow specimens from AML children were significantly lower than that in non-malignant controls (P<0.001). Statistically, AML children with low miR-122 expression more frequently had large white blood cell count (P=0.022), French-American-British classification subtype M7 (P<0.001), unfavorable cytogenetics (P=0.002) and day 7 response to the treatment (P=0.036), short relapse-free (P=0.001) and overall (P=0.008) survivals than those with high expression. Multivariate analysis also determined that miR-122 expression was an independent prognostic factor for both relapse-free and overall survivals. Functionally, the enforced expression of miR-122 in AML cell lines efficiently suppressed cell proliferation and reduced the ratio of S-phase cells in vitro (all P<0.05). In conclusion, the abnormal expression of miR-122 may be a marker of the aggressive progression in childhood AML. Importantly, its downregulation may serve as a prognostic factor to predict poor outcome. Our study also reveal that miR-122 may function as a tumor suppressor in childhood AML, highlighting a new therapeutic strategy for this malignancy.