miR-339 Promotes Development of Stem Cell Leukemia/Lymphoma Syndrome via Downregulation of the BCL2L11 and BAX Proapoptotic Genes.

The development of myeloid and lymphoid neoplasms related to overexpression of FGFR1 kinases as a result of chromosome translocations depends on the promotion of a stem cell phenotype, suppression of terminal differentiation, and resistance to apoptosis. These phenotypes are related to the stem cell leukemia/lymphoma syndrome (SCLL), which arises through the effects of the activated FGFR1 kinase on gene transcription, which includes miRNA dysregulation. In a screen for miRNAs that are directly regulated by FGFR1, and which stimulate cell proliferation and survival, we identified miR-339-5p, which is highly upregulated in cells carrying various different chimeric kinases. Overexpression of miR-339-5p in SCLL cell types enhances cell survival and inhibition of its function leads to reduced cell viability. miR-339-5p overexpression protects cells from the consequences of FGFR1 inactivation, promoting cell-cycle progression and reduced apoptosis. Transient luciferase reporter assays and qRT-PCR detection of endogenous miR-339-5p expression in stably transduced cell lines demonstrated that BCR-FGFR1 can directly regulate miR-339-5p expression. This correlation between miR-339-5p and FGFR1 expression is also seen in primary human B-cell precursor acute lymphoblastic leukemia. In a screen to identify targets of miR-339-5p, we identified and verified the BCL2L11 and BAX genes, which can promote apoptosis. In vivo, SCLL cells forced to overexpress miR-339-5p show a more rapid onset of disease and poorer survival compared with parental cells expressing endogenous levels of miR-339-5p. Analysis of human primary B-cell precursor ALL shows a significant higher expression of miR339-5p compared with the two cohorts of CLL patient samples, suggesting direct roles in disease progression and supporting the evidence generated in mouse models of SCLL.Significance: Proapoptiotic genes that are direct targets of miR-339-5p significantly influence promotion and aggressive development of leukemia/lymphomas associated with FGFR1 overexpression. Cancer Res; 78(13); 3522-31. ©2018 AACR. ©2018 American Association for Cancer Research.