Abstract P3-10-03: Enrichment of pro-oncogenic immune miRNAs in exosomes by cyclin D1, promote cancer stem cell expansion

Abstract The cyclin D1 (CCND1) gene, encodes the regulatory subunit of a holoenzyme that phosphorylates and inactivates the Rb protein. Cyclin D1 overexpression occurs in up to 50% of human breast cancers. Cyclin D1, governs the expression (1,3), processing (2), 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 (4). Through base-pairing to the complementary sequence in 3’ untranslated region (3’ UTR) of mRNA, miRNAs participate in diverse biological processes. A subset of miRNA regulate the ageing of innate and adaptive immune cells, which has been associated with breast cancer initiation, progression and therapy resistance. Immuno-miRs, ( miR-21 and miR-93), bind to the 3′-UTR region of mRNAs, and binding to- and or activate Toll-Like Receptor 8 (TLR8) in surrounding cells of the immune system. Exosomes which contain constituents of their cell of origin, including mRNA and miRNA are found in the tumor microenvironment and participate in therapy resistance, cancer metastasis and the metastatic niche. Herein, tet-inducible cyclin D1 shRNA knock down in MCF-7 breast cancer cells reduced MCF-7 cell proliferation and mammosphere formation. Exosomes isolated from wildtype and cyclin D1 knock-down MCF-7 cell culture media, showed that exosomes from cyclin D1 knock down cells decreased proliferation of both wildtype and cyclin D1 knock-down cells. Furthermore, wildtype exosomes partially reversed the cyclin D1 knock-down effects. Cyclin D1 knock-down exosomes decreased mammosphere formation of wildtype MCF-7 cells and wildtype 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. >85% of the cyclin D1-induced exosome miRNA transcripts were the immune-mIR, miR21. hsa-mir-21 which has documented tumor promoting function, was the most enriched miRNAs in cyclin D1 knock-down exosomes. In contrast, exosome abundance of the transcripts for hsa-mir-16 and hsa-mir-92a, both of which were showed as tumor suppressor in breast cancer cells, were reduced by cyclin D1 shRNA. The cyclin D1-mediated miRNA exosome content may contribute to tumor initiation and progression through heterotypic expansion of cancer stem cells. 1.Yu, Z., etal ., A cyclin D1/microRNA 17/20 regulatory feedback loop in control of breast cancer cell proliferation. J Cell Biol. 2008 Aug 11; 182(3): p. 509-17. 2.Yu., Z,., et. al. Cyclin D1 induction of Dicer governs microRNA processing and expression in breast cancer. Nat Commun 2013;4:2812.doi: 10.1038/ncomms3812. 3.Yu Z, et al. Cyclin D1- Mediated MicroRNA Expression Signature in Breast Cancer Subtype and Outcome. Theranostics, 2018 Mar 11,8:8, 2251-2263. 4.Lü J, et al. Cyclin D1 promotes secretion of pro-oncogenic immuno-miRNAs and piRNAs. Clin Sci (Lond). 2020 Mar 27. pii: CS20191318. doi: 10.1042/CS20191318. [Epub ahead of print]PMID:32219337 Citation Format: Xuanmao Jiao, Chongwen Xu, Lifeng Tian, Zhao Zhang, Anthony W Ashton, Zhiping Li, Richard G Pestell. Enrichment of pro-oncogenic immune miRNAs in exosomes by cyclin D1, promote cancer stem cell expansion [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P3-10-03.