Exosomal microRNA-20b-5p contributes to cytarabine resistance in acute myeloid leukemia via the microtubule-associated serine/threonine kinase-like-phosphatidylinositol 3-kinase-protein kinase B signaling axis

Background: Cytarabine (Ara-C) resistance limits durable remission in acute myeloid leukemia (AML). A working model posits that exosomal miR-20b-5p promotes resistance by repressing MASTL and sustaining PI3K-AKT signaling.

Methods: Ara-C-resistant sublines were generated. Exosomes were purified and validated by TEM, NTA, and immunoblotting. Functional transfer used exosome-depleted serum with GW4869 and EV-depleted medium controls. MASTL targeting was tested with 3'-UTR dual-luciferase reporters and biotinylated-miRNA pull-down. Proteomics profiled pathways. Xenograft studies evaluated in vivo effects; MK-2206 probed Akt dependence.

Results: Resistant-cell exosomes reduced Ara-C sensitivity of matched parental cells, and were enriched for miR-20b-5p; controls had no effect. Reporter and pull-down assays supported direct binding to the MASTL 3'-UTR, with reduced MASTL mRNA/protein and increased p-PI3K/p-AKT. Re-expression of MASTL lacking the 3'-UTR and Akt inhibition each partially reversed signaling and drug-response phenotypes. In relapsed blasts, a miRNA inhibitor restored MASTL and lowered p-PI3K. In vivo, leukemia-derived exosomes increased leukemic burden, consistent with an exosomal miR-20b-5p-MASTL-PI3K-AKT axis.

Conclusions: Exosomal miR-20b-5p represses MASTL, remodels PI3K-AKT, and attenuates Ara-C responses in AML models. Seed-mutant reporters and 3'-UTR-independent rescue support target specificity. Findings are mechanistic and hypothesis-generating; clinical relevance requires confirmation in primary blasts and prospective validation.