Background: Prostate cancer (PCa), the second leading cause of death in American men, includes distinct genetic subtypes with distinct therapeutic vulnerabilities. The DACH1 gene encodes a winged helix/Forkhead DNA-binding protein that competes for binding to FOXM1 sites. Methods: Analysis of DACH1 gene deletion and gene expression was conducted from public data bases and human prostate cancer samples. Transgenic mice were generated in which the Dach1 gene was deleted in the prostate of prostate Oncomice. Cells derived from Dach1 gene deletion mice and human prostate cancer cell lines with Dach1 knockdown were analyzed for DNA damage repair responses. Results: DACH1 gene deletion within the 13q21.31-q21.33 region, occurred in up to 18% of human PCa, and was associated with increased AR activity, and poor prognosis. DACH1 homozygous deletions more frequent in the metastatic site than in the primary tumors (Mich: 10% vs. 18%, N=59; FHCRC: 4% vs.11%, N= 54, SU2C: not profiled vs. 3.3, N=150). The prevalence of DACH1 heterozygous deletions was higher in the metastatic lesions than in primary tumors within a given cohort for three of six cohorts (Mich: 27.3% vs. 36%, N=59; FHCRC: 15% vs. 59%, N=54; SU2C: 0% vs. 26%, N=150, respectively). The patients with homozygous DACH1 deletions had reduced overall survival (medians of 84 vs. 120 months, N=667, log rank test P=9.3x10-3). Low DACH1 gene expression (expressed as a z-score with a z-score threshold of -1.25) was significantly correlated with earlier biochemical recurrence (BCR, log rank p value = 4.7x10-4, n=79). In prostate OncoMice, prostate-specific deletion of the Dach1 gene enhanced prostatic intraepithelial neoplasia (PIN) and was associated with increased DNA damage. Reduced Dach1 increased DNA damage in responses to genotoxic stresses. DACH1 was recruited to sites of DNA damage, augmenting recruitment of Ku70/Ku80. Reduced Dach1 expression was associated with resistance to TGFβ kinase and PARP inhibitors. Conclusions: Reduced Dach1 expression may define a subclass of PCa that warrants specific therapies. Citation Format: Zhiping Li, Xuanmao Jiao, Gordon Robertson, Gabriele Di Sante, Anthony W. Ashton, Agnese DiRocco, Min Wang, Jun Zhao, Sankar Addya, Chenguang Wang, Peter A. McCue, Andrew P. South, Carlos Cordon-Cardo, Runzhi Liu, Kishan Patel, Rasha Hamid, Jorim Parmar, James B. DuHadaway, Nikolaus Schultz, Andrew Kossenkov, Lai Yee Phoon, Hao Chen, Li Lan, Yunguang Sun, Kenneth A. Iczkowski, Hallgeir Rui, Richard G. Pestell. The DACH1 gene is frequently deleted in prostate cancer, restrains prostatic intraepithelial neoplasia, augments DNA damage repair and predicts therapy responses [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2598.

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.