IGF2BP3 remodels RISC occupancy to control microRNA targeting in leukemia.

IGF2BP3 is an oncofetal RNA-binding protein that promotes leukemogenesis, but the mechanisms by which it remodels post-transcriptional gene regulation remain incompletely understood. Because IGF2BP3 binds extensively within 3' untranslated regions and has been implicated in microRNA (miRNA)-mediated regulation, we asked whether IGF2BP3 controls access of the RNA-induced silencing complex (RISC) to endogenous messenger RNA (mRNA) targets in leukemia cells. Using AGO2 miR-eCLIP in control and IGF2BP3-deficient MLL-AF4 B-lymphoblastic leukemia cells, we found that loss of IGF2BP3 broadly redistributes AGO2 occupancy toward 3' UTRs of IGF2BP3-bound transcripts. AGO2 gains were enriched near miRNA target sites and on transcripts associated with proliferative and oncogenic pathways. Chimeric AGO2-miRNA reads revealed transcript- and miRNA-specific remodeling of RISC interactions, with enhanced miR-181 occupancy on oncogenic transcripts following IGF2BP3 loss. Functionally, miR-181a overexpression impaired leukemic cell growth, partially phenocopying IGF2BP3 deletion. Motif analyses indicated that IGF2BP3 and AGO2 converge on related 3' UTR sequence environments, while biochemical competition assays demonstrated that purified IGF2BP3 can displace AGO2-containing RISC complexes from a shared RNA substrate. Together, these findings support a model in which IGF2BP3 restricts RISC access to select 3' UTR regulatory elements, thereby reshaping miRNA-target interactions and sustaining leukemic gene expression programs. Rather than acting solely as an mRNA stabilizing factor, IGF2BP3 functions as a transcript-selective regulator of RISC accessibility in leukemia.