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Abstract 4142: Conformational dynamics of the chimeric kinase DNAJB1-PRKACA, the driver for fibrolamellar hepatocellular carcinoma

In fibrolamellar hepatocellular carcinoma (FLC) there is a single common genetic alteration in all tumors: A deletion in one copy of chromosome 19 resulting in the fusion of the first exon of DNAJB1, encoding the J-domain of heat shock protein 40, with exons 2-10 of the catalytic subunit of protein kinase A, PRKACA [1]. This produces an enzymatically active chimeric protein. Expression of the chimera in mouse liver either by recreating the deletion by CRISPR/Cas9, or expression, in trans, by a transposon is sufficient to produce FLC [2]. We used molecular dynamics simulations, NMR, and SAXS to analyze the conformational dynamics of the native and chimeric kinase. The most significant differences were in the amino domain with the chimera in an ensemble of conformations. Some structures had the J-domain tucked under the large lobe of the kinase, similar to that reported in the crystal structure, and in others the J-domain was dislodged from the core of the kinase, swinging free in solution. These simulated dislodged states were captured experimentally both by NMR and small angle X-ray scattering. Modeling of the different conformations onto the RIIβ holoenzyme revealed no obvious steric interactions suggesting that the J-domain does not preclude formation of the holoenzyme. The flexible conformations appear to be independent of the nucleotide/substrate binding mode as they were observed in ATP, ADP, Apo, and ATP-PKI bound states. [1] Honeyman, J. N. et al. Detection of a recurrent DNAJB1-PRKACA chimeric transcript in fibrolamellar hepatocellular carcinoma. Science 343, 1010-1014 (2014). [2] Kastenhuber, E. R. et al. DNAJB1-PRKACA fusion kinase interacts with β-catenin and the liver regenerative response to drive fibrolamellar hepatocellular carcinoma. Proc. Natl. Acad. Sci. 201716483 (2017). doi:10.1073/pnas.1716483114 Citation Format: Michael D. Tomasini, Yingiie Wang, Adak Karamafrooz, James Hall, Susan S. Taylor, Thijs Beuming, Gianluigi Veglia, Sanford M. Simon. Conformational dynamics of the chimeric kinase DNAJB1-PRKACA, the driver for fibrolamellar hepatocellular carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4142.