TY - JOUR T1 - Telomerase reactivation induces progression of mouse Braf<sup>V600E</sup>-driven thyroid cancers without telomere lengthening JF - bioRxiv DO - 10.1101/2023.01.24.525280 SP - 2023.01.24.525280 AU - Iñigo Landa AU - Caitlin EM Thornton AU - Bin Xu AU - Jacob Haase AU - Gnana P. Krishnamoorthy AU - Jingzhu Hao AU - Jeffrey A Knauf AU - Zachary T Herbert AU - María A Blasco AU - Ronald Ghossein AU - James A Fagin Y1 - 2023/01/01 UR - http://biorxiv.org/content/early/2023/01/24/2023.01.24.525280.abstract N2 - Mutations in the promoter of the telomerase reverse transcriptase (TERT) gene are the paradigm of a cross-cancer alteration in a non-coding region. TERT promoter mutations (TPMs) are biomarkers of poor prognosis in several tumors, including thyroid cancers. TPMs enhance TERT transcription, which is otherwise silenced in adult tissues, thus reactivating a bona fide oncoprotein. To study TERT deregulation and its downstream consequences, we generated a Tert mutant promoter mouse model via CRISPR/Cas9 engineering of the murine equivalent locus (Tert-123C&gt;T) and crossed it with thyroid-specific BrafV600E-mutant mice. We also employed an alternative model of Tert overexpression (K5-Tert). Whereas all BrafV600E animals developed well-differentiated papillary thyroid tumors, 29% and 36% of BrafV600E+Tert-123C&gt;T and BrafV600E+K5-Tert mice progressed to poorly differentiated thyroid cancers at week 20, respectively. Braf+Tert tumors showed increased mitosis and necrosis in areas of solid growth, and older animals from these cohorts displayed anaplastic-like features, i.e., spindle cells and macrophage infiltration. Murine Tert promoter mutation increased Tert transcription in vitro and in vivo, but temporal and intra-tumoral heterogeneity was observed. RNA-sequencing of thyroid tumor cells showed that processes other than the canonical Tert-mediated telomere maintenance role operate in these specimens. Pathway analysis showed that MAPK and PI3K/AKT signaling, as well as processes not previously associated with this tumor etiology, involving cytokine and chemokine signaling, were overactivated. Braf+Tert animals remained responsive to MAPK pathway inhibitors. These models constitute useful pre-clinical tools to understand the cell-autonomous and microenvironment-related consequences of Tert-mediated progression in advanced thyroid cancers and other aggressive tumors carrying TPMs.Competing Interest StatementThe authors have declared no competing interest. ER -