Abstract C012: Dissemination of retrotransposable elements from the non-coding genome in tumor-derived extracellular vesicles target stromal and immune cells to induce local and systemic inflammation
Authors: Radvanyi Laszlo , Evdokimova Valentina , Ruzanov Peter , Zhang Zhenbo , Sorenson Poul , Gassmann Hendrik , Burdach Stefan , Stein Lincoln D. 
Published: November 2024

The majority of the human genome (&gt;70%) contains non-coding DNA consisting of retrotransposable elements (RTE), such as LINE-1, SINE/Alu elements, human endogenous retroviruses (HERV), and satellite repeat DNA (Hsat2 and Hsat3). The expression of these elements is suppressed in normal adult tissues but are abnormally expressed in many cancers. Another key mechanism in cancer initiation and progression is the release of tumor-derived extracellular vesicles (EV) that are long-distance communication vehicles propagating signals from tumors inducing metabolic changes, immune dysregulation and promoting metastases across the body. Our work has uncovered a link between RTE, HERV and Hsat expression in cancer and EV in driving tumor progression and immune dysregulation. W hole transcriptome sequencing of EV derived from several different cancer cell lines and patient samples, including Ewing sarcoma, osteosarcoma, prostate, pancreatic, and breast cancer found that RTE, HERV and Hsat2,3 transcripts are highly enriched in EV versus coding region transcripts and in much higher abundance than in the tumor cell themselves. Tumor-derived EV contained dsRNA, dsDNA and RNA:DNA hybrids from these non-coding regions. Plasma EV isolated from both metastatic and non-metastatic patients also showed an enrichment of these RTE, HERV and Hsat2,3 elements and clearly differentiated healthy, normal donor EV that had little or no detectable signal. Evidence of local dissemination of these non-coding elements in EV was also found in vivo in tumor xenografts that showed transfer of Hsat2,3 transcripts into the murine stroma that naturally lack these satellite repeats. Treatment of fibroblasts and myeloid cells with tumor-derived EV triggered innate immune responses via type I IFN and pro-inflammatory cytokines, including IL-1beta, IL-6, IL-8, and TNFalpha owing to the pathogen-like nucleic acid sequences (viral mimicry) of these elements. These EV-induced chronic inflammatory effects were mainly induced through the cGAS-STING nucleic acid sensing pathway. Evidence of DNA damage in stromal fibroblasts and induced senescence was also found as a result of EV treatment. A key element of RTE is the expression of LINE-1 and HERV derived reverse transcriptase (RT) that propagates the action of RTE via RNA:DNA hybrids, dsDNA and retrotransposition in the genome. In a spontaneous estradiol-driven breast cancer model in ACI rats, long-term treatment with an HIV RT inhibitor (lamivudine/3TC) inhibited breast tumor development associated with reduced RTE activation in the mammary gland and in circulating immune cells as well as reduced chronic systemic innate inflammation. Our results suggest that RTE, HERV and Hsat activation, together with their local and systemic dissemination in EV plays an important role in cancer initiation and progression associated with chronic inflammation. We also suggest that abnormal dissemination of these activated non-coding elements in EV may also play a role in "inflammaging" facilitating not only cancer but also other chronic diseases.

Citation Format: Laszlo Radvanyi, Valentina Evdokimova, Peter Ruzanov, Zhenbo Zhang, Poul Sorenson, Hendrik Gassmann, Stefan Burdach, Lincoln D. Stein. Dissemination of retrotransposable elements from the non-coding genome in tumor-derived extracellular vesicles target stromal and immune cells to induce local and systemic inflammation [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Tumor-body Interactions: The Roles of Micro- and Macroenvironment in Cancer; 2024 Nov 17-20; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(22_Suppl):Abstract nr C012.