Abstract PO-063: Environment-induced YAP1 transcriptional reprogramming drives head and neck cancer
Authors: Masuda Muneyuki , Omori Hirofumi , Sato Kuniaki , Penninger Josef , Gutkind Silvio 
Published: September 2023

Abstract
Background: The biology of head and neck cancer (HNC) has been explained by the field carcinogenesis theory in which accumulated abnormalities (mainly gene mutations) caused by environmental stresses promote carcinogenesis. However, as clearly demonstrated by recent studies (Yokoyama et.al, Nature 2019; Hedberg et.al, JCI 2016), the genetic landscape of HNC (i.e., the loss-of-function mutations in tumor suppressor genes) fails to account for the onset and metastatic ability of HNC. In addition to being mutagen, environmental stresses induce oncogenic transcriptional programs (e.g., tissue regeneration). In this context, we have advanced our study based on a perspective that HNC is a symbiotic evolving system, highly dependent on transcriptional reprograming. Recently we succeeded to develop an ultra-rapid mouse carcinogenesis model (4W) induced by a transcriptional coactivator YAP1 (Omori et al, Sci Adv 2020) and are conducting integrative epigenetic analyses to elucidate how YAP1-induced transcriptional reprogramming drives HNC. Material and methods: Mouse tumors and a cell line and human HNC cell lines and tissue samples were subject to WES, WGBS, RNA-seq, Chip-seq (H3K27ac, YAP1, H3K9me2/3), and IHC. Results: YAP1-induced mouse tumors and cell lines demonstrated that YAP1 epigenetically causes carcinogenesis without affecting genome-wide chromatin confirmation, but inducing hypomethylation on the super enhancers (SE) of genes related to tissue regeneration (i.e., recapitulation of wounds that don’t heal condition). Poor prognosis was associated with YAP1-induced carcinogenesis gene module in the TCGA data (p = 0.00033) and with the level of YAP1nuclear protein in the 119 HNC samples (p = 0.0116). RNA-seq and Chip-seq with HNC cell lines showed that YAP1 is essential for the assembly of SE and that YAP1-related SE module including IL6 was associated with unfavorable survival in the TCGA data (p = 0.031). The existence of IL6-YAP1 feed-forward loop was confirmed in vitro assays. EEM and motif assays revealed that YAP1, collaborating with PITX2 transcriptional factor (TF), regulates TGF-beta-induced EMT and CAF, suggesting the involvement of YAP1 and PITX2 in the partial-EMT process, which was reported to play an important role in the nodal metastases of HNC (Puram et.al, Cell 2017). In the TCGA data, YAP1 target module demonstrated a significant correlation with p-EMT score or TGF-beta induced LRRC15 expressing CAF module. In the invasion front, YAP1 positive cancer cells co-existed with LRRC15 positive CAF. In vitro assays and Chip-seq on human HNC samples support the significance of collaboration of YAP1 and PITX2 in SE for nodal metastases. Co-expression of YAP1 plus PITX2 or BRD4 further worsened the prognosis than the individual factor alone. Conclusions: Collectively, our data indicate that YAP1-induced transcriptional reprograming, triggered and activated in the HNC specific tumor microenvironment, may function as a potent engine and thereby drive symbiotic evolution of HNC.
Citation Format: Muneyuki Masuda, Hirofumi Omori, Kuniaki Sato, Josef Penninger, Silvio Gutkind. Environment-induced YAP1 transcriptional reprogramming drives head and neck cancer [abstract]. In: Proceedings of the AACR-AHNS Head and Neck Cancer Conference: Innovating through Basic, Clinical, and Translational Research; 2023 Jul 7-8; Montreal, QC, Canada. Philadelphia (PA): AACR; Clin Cancer Res 2023;29(18_Suppl):Abstract nr PO-063.