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Abstract B04: High-level expression of oncogenic KRAS is required to transform LKB1 mutant tissue in vivo

Although activating mutations in the GTPase KRAS are oncogenic and implicated in various malignancies, mutations in KRAS alone are inefficient to transform epithelia. In lung adenocarcinoma, KRAS mutations occur at high frequency and co-segregate with loss of the LKB1 tumor suppressor, a master serine/threonine kinase that phosphorylates and activates multiple AMPK family kinases to control energy homeostasis, cell polarity, and cell:matrix signaling. Despite our current knowledge of LKB1 biology, the complexity of the signaling pathway has precluded investigations into the precise mechanism by which alteration of this kinase contributes to oncogenic transformation and tumor progression in vivo. In the present study, we introduced mutations in Kras and Lkb1 in the genetically tractable organism Drosophila melanogaster. We show that low-level expression of oncogenic Kras (KrasLow) promotes the survival of Lkb1-mutant tissue, eventually leading to a G1 arrest, and concomitant overgrowth of the surrounding tumor microenvironment. Alternatively, high-level expression of oncogenic Kras (KrasHigh) promotes the neoplastic transformation of Lkb1-mutant tissue, leading to autonomous growth and increased cell cycle progression, invasion of mutant tissue into the brain, and the survival and growth of explanted tumor tissue in a wild-type Drosophila host. Interestingly, phosphorylation of the canonical Lkb1 target AMPK is maintained in KrasHigh/Lkb1 neoplastic tissue, but not in KrasLow/Lkb1 tissue. Finally, we analyzed TCGA Pan Lung Cancer data and show that high-level, but not low-level, expression of oncogenic KRAS results in worse overall survival in the context of LKB1 loss. Taken together, these data suggest that increasing levels of oncogenic KRAS, perhaps through mutant KRAS copy gains, are a driving event in the malignant transformation of LKB1-mutant tissue, and that the rewired AMPK signaling axis may offer a potential therapeutic target for patients with this subset of mutations. Citation Format: Briana B. Rackley, Chang-Soo Seong, Melissa Gilbert-Ross. High-level expression of oncogenic KRAS is required to transform LKB1 mutant tissue in vivo [abstract]. In: Proceedings of the AACR Special Conference on Targeting RAS-Driven Cancers; 2018 Dec 9-12; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2020;18(5_Suppl):Abstract nr B04.