Abstract 2356: Cyclin D1 mediated exosomes are enriched for pro-oncogenic miRNAs and promote cancer stem cell expansion

miRNAs are a class of endogenous noncoding small RNAs that participate in diverse biological processes through base-pairing to the complementary sequence in 39 untranslated region (39 UTR) of mRNA Specific miRNA have been associated with the initiation, progression and therapy resistance and regulate immunological processes including the activation and ageing of innate and adaptive immune cells. Immuno-miRs, including. miR-21 and miR-93, regulate immune function in the tumor microenvironment by binding to the 3′-UTR region of target mRNAs, or by binding to- and activating Toll-Like Receptor 8 (TLR8) in surrounding cells of the immune system. The cyclin D1 (CCND1) gene, which encodes the regulatory subunit of a holoenzyme that phosphorylates and inactivates the Rb protein, is overexpressed in up to 50% of human breast cancers. Cyclin D1, governs the expression, processing, the secretion and the relative proportion of secreted non-coding RNA subtypes (miRNA, rRNA, tRNA, CDBox, scRNA, HAcaBox. scaRNA, piRNA) in human breast cancer and the secretion of piRNA. Exosomes, which consist of a lipid bilayer membrane surrounding a small cytosol, contain constituents of their cell of origin, including mRNA and miRNA. Exosomes in the tumor microenvironment, participate in therapy resistance, cancer metastasis and the metastatic niche. Herein, knock down of cyclin D1 in MCF-7 cells with tet-inducible cyclin D1 shRNA decreased MCF-7 cell proliferation and mammosphere formation. Exosomes isolated from wild-type and cyclin D1 knock-down MCF-7 cell culture media, showed that exosomes from cyclin D1 knock down cells dramatically decreased proliferation of both wild-type and cyclin D1 knock-down cells, whereas the wild-type exosomes partially reversed the cyclin D1 knock down effects. Cyclin D1 knock-down exosomes decreased mammosphere formation of wild-type MCF-7 cells and wild-type exosomes increased mammosphere formation of cyclin D1 knock-down cells. miRNA profiles within the exosomes, showed that cyclin D1 regulated the abundance of miRNA within exosomes. The pattern of miRNA within exosomes regulated by cyclin D1 were enriched for miRNA governing mesenchymal epithelial transition and the induction of stem cell function. The most enriched miRNA in cyclin D1 wild-type exosomes was hsa-mir-21 which was recognized tumor promoting function, whereas the most enriched miRNAs in cyclin D1 knock-down exosomes were has-mir-16 and has-mir-92a, both of which were shown as tumor suppressor in breast cancer cells. The immune-miR miR-21 represented >85% of the cyclin D1-induced exosome miRNA transcripts, The cyclin D1-mediated miRNA exosome content may contribute to tumor initiation and progression through heterotypic expansion of cancer stem cells. Citation Format: Xuanmao Jiao, Chongwen Xu, Lifeng Tian, Zhao Zhang, Anthony W. Ashton, Zhiping Li, Richard G. Pestell. Cyclin D1 mediated exosomes are enriched for pro-oncogenic miRNAs and promote cancer stem cell expansion [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2356.