Generation of primary sarcoma mouse models through CRISPR/Cas9 mediated activation of Yap1

Soft tissue sarcomas (STSs) are rare heterogeneous cancers arising from diverse connective tissues. Undifferentiated pleomorphic sarcomas (UPSs), the most common sarcomas diagnosed in adult patients, are complex karyotypes of nonspecific genetic alterations. To date, the molecular mechanisms by which UPSs develop in patients are still poorly understood, which hinders precision medicine to treat the disease. Primary UPS mouse model generated by conditional activation of KrasG12D and mutation of Trp53 (KP mouse model) is currently used for studying sarcoma biology, imaging, and preclinical trials. However, Kras mutation is rarely identified in human UPSs. We recently showed that injury can replace KrasG12D to induce primary UPSs in mouse models of conditional mutation of Trp53. Furthermore, our whole-exome sequencing determined Yap1 amplification in some injury-induced sarcomas. Moreover, it is also shown that a subset of human UPSs may be driven by Hippo pathway. In addition, it is reported that activation of mutant Yap1 induced primary rhabdomyosarcomas (RMSs) in mouse models. CRISPR/Cas9-mediated genetic mutation has been applied to rapidly create mouse models of cancers, including sarcoma, with spatial and temporal control. However, rare studies have been performed to investigate whether CRISPR/Cas9-mediated activation of endogenous oncogenes could generate primary cancer models. Thus, we applied CRISPR/Cas9 technology to test whether activation of endogenous Yap1 can induce cell transformation or even generate primary UPSs in mouse models. Our results showed that CRISPR/dCas9-p300-mediated activation of endogenous Yap1 resulted in transformation of KrasG12D immortalized mouse embryonic fibroblasts (MEFs) as well as Trp53 knockout MEFs. Moreover, we are currently applying our recently developed in vivo CRISPR/Cas9 delivery method combined with Sleeping Beauty transposon system to investigate whether we are able to develop primary UPSs in mouse models by activating Yap1. If successful, it will further allow us to perform CRISPR/Cas9-mediated direct in vivo activation screen to identify other oncogene drivers for sarcomagenesis. In conclusion, primary sarcoma mouse models generated by CRISPR/Cas9-mediated activation will be an indispensable platform for studying sarcoma biology and precision medicine. Citation Format: Jianguo Huang, Eric Xu, David Van Mater, David G Kirsch. Generation of primary sarcoma mouse models through CRISPR/Cas9 mediated activation of Yap1 [abstract]. In: Proceedings of the AACR Special Conference on the Hippo Pathway: Signaling, Cancer, and Beyond; 2019 May 8-11; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2020;18(8_Suppl):Abstract nr A03.