Figure S5. BMM-induced MIR300 anti-proliferative and PP2A-activating functions impair NK cell immune-response. A, PP2A-dependent regulation of MIR300 and miR-155 validated pathways predicted to occur also in the bone marrow endosteal niche. B, Effect of hypoxia (1% O2, 7 days) on CFSE+NK cell proliferation (% CFSE mean of fluorescence). C, HS-5 exosomal miRNAs reported as negative regulators of NK cell proliferation/activity and their experimentally validated targets. miRNA RNAseq was performed on an Illumina platform using libraries derived from 100 ng RNA/sample from HS-5 exosome purifications (n=3). D, Precursor (pre-miR-155) miR-155 (BIC) levels in resting and IL-12/IL-18 (18h)-stimulated NK cells exposed (48h) to HS-5 exosomes. E, Effect of hypoxia (1% O2) and HS-5 CM (48h) on TUG1 expression in CD56+CD3- primary NK and NK-92 cells. F, Effect of CpG-TUG1-shRNA and CpG-scramble (200-500 nM, 5 days) on IL-2-induced NK cell proliferation (% cell number). Data are represented as mean+/-SEM.
ARTICLE ABSTRACTPersistence of drug-resistant quiescent leukemic stem cells (LSC) and impaired natural killer (NK) cell immune response account for relapse of chronic myelogenous leukemia (CML). Inactivation of protein phosphatase 2A (PP2A) is essential for CML-quiescent LSC survival and NK cell antitumor activity. Here we show that MIR300 has antiproliferative and PP2A-activating functions that are dose dependently differentially induced by CCND2/CDK6 and SET inhibition, respectively. MIR300 is upregulated in CML LSCs and NK cells by bone marrow microenvironment (BMM) signals to induce quiescence and impair immune response, respectively. Conversely, BCR-ABL1 downregulates MIR300 in CML progenitors to prevent growth arrest and PP2A-mediated apoptosis. Quiescent LSCs escape apoptosis by upregulating TUG1 long noncoding RNA that uncouples and limits MIR300 function to cytostasis. Genetic and pharmacologic MIR300 modulation and/or PP2A-activating drug treatment restore NK cell activity, inhibit BMM-induced growth arrest, and selectively trigger LSC apoptosis in vitro and in patient-derived xenografts; hence, the importance of MIR300 and PP2A activity for CML development and therapy.
Tumor-naïve microenvironment–induced MIR300 is the only tumor suppressor miRNA that induces CML LSC quiescence while inhibiting NK cell antitumor immune response, and CML LSC/progenitor cell apoptosis through its anti-proliferative and PP2A-activating functions, respectively. Thus, the importance of MIR300 and PP2A-activating drugs for formation/survival and eradication of drug-resistant CML LSCs, respectively.See related commentary by Broxmeyer, p. 13.This article is highlighted in the In This Issue feature, p. 5