Glucocorticoid-regulated microRNAs and mirtrons in human acute lymphoblastic leukemia

Glucocorticoids (GC) have a major impact on the biology of normal and malignant cells of the lymphoid lineage. This includes induction of apoptosis which is exploited in the therapy of acute lymphoblastic leukemia (ALL) and related lymphoid malignancies. MicroRNAs (miRNAs), and the related mirtrons, are ~22 nucleotide RNA molecules implicated in the control of essential biological functions including proliferation, differentiation and apoptosis. They derive from polymerase-II transcripts but whether GCs regulate miRNA/mirtron-encoding transcription units is not known. We investigated miRNA/mirtron expression and GC regulation in 8 ALL in vitro models and 13 ALL children undergoing systemic GC monotherapy using a combination of expression profiling techniques, real time RT-PCR and northern blotting to detect mature miRNAs/mirtrons and/or their precursors. We identified a GC-regulated mirtron (miR-1233) and a number of GC-regulated miRNAs, including the myeloid-specific miR-223 and the apoptosis and cell cycle arrest-inducing mir15~16 cluster. However, the response was heterogeneous in individual patients and cell lines, the extent of regulation was moderate, and functional analyses of the most promising candidates (miR223 and the miR15~16 cluster) revealed little, if any effect, on cell cycle progression and survival. Thus, although GCs affect miRNA expression in ALL cells, these regulations may not be major contributors to the anti-leukemic GC effects. Keywords: exon analysis Glucocorticoid-sensitive T-ALL cell line CCRF-CEM-C7H2 was treated in 3 independent experiments either with 100nM dexametasone (a glucocorticoid) or 0.1% ethanol as an empty carrier control. Samples were taken at various timepoints (30 minutes, 2, 6 and 24 hours), RNA extracted and hybridized onto Affymetrix Exon microarrays (HuEx 1.0 st).