The Epigenetic Regulator, G9a, Is A Kras-Inducible Protein And Its Inactivation Inhibits Panin Formation By This Oncogene

Pancreatic ductular adenocarcinoma (PDAC) ranks fourth as a cause of cancer death in the USA and is almost universally fatal, with the annual number of deaths equivalent to the number of newly diagnosed cases. Valuable research in the field has revealed genetic aberrations that contribute to PDAC development and progression, with KRAS being one of the most frequent mutations in more than 90% of patient samples. However, to date, any efforts to directly target KRAS have failed in the clinic. Thus, there is indisputably an urgent need to further improve our understanding of molecular mechanisms underlying PDAC development as to identify novel therapeutic targets, including druggable important downstream targets and nodes orchestrated by oncogenic KRAS. In particular, we are interested in epigenetic pathways involved in PDAC development and progression due to the potential reversibility of any alteration, unlike genetic mutation. In the current study, using a cell model that allows inducible expression of mutant KRASG12D, we find that protein levels of the dimethyl-K9H3 histone methyl transferase (HMT), G9a, and its complex partners are increased in response to activation of the oncogenic Kras pathway. Furthermore, the activation of this oncogenic pathway results in the formation of the G9a-GLP-Wiz trimer complex, as determined by affinity protein purification, combined with mass spectrometry. In vivo experiments involving the cross of the Pdx1-CRE/LSL-KRASG12D mice with G9afl/fl animals demonstrate that a loss of the H3K9Me2 mark in the nucleus of exocrine cells is accompanied by a significantly reduced number of PanIN lesions. RNA-Seq experiments from these animals reveal that these mice have reduced levels of typical molecular markers of PanINs. In addition, these experiments show changes in the levels in several genes, which have been previously been shown to synergize with Kras to mediate pancreatic cancer initiation. Congruently, pharmacological inhibition of G9a using BRD4770 displays an inhibitory effect on KRASG12D-induced cell proliferation. Combined, these data provide evidence for a key role of the meK9H3-G9a pathway as a mediator of the oncogenic Kras response and defines a novel point of potential therapeutic intervention for PDAC. Citation Format: Angela Mathison, Ann Salmonson, Brooke Paradise, Mckenna Missfeldt, Juan Iovanna, Daniel Billadeau, Raul Urrutia, Gwen Lomberk. The epigenetic regulator, G9a, is a KRAS-inducible protein and its inactivation inhibits PanIN formation by this oncogene [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1391. doi:10.1158/1538-7445.AM2017-1391