Ubiquitin-independent, Proteasome-mediated targeted degradation of KRAS in pancreatic adenocarcinoma cells using an engineered ornithine decarboxylase/antizyme system.

The oncogene KRAS not only promotes the tumorigenesis of pancreatic cancers but also is required for the malignant progression and metastasis of these cancers. Many methods have been explored to influence the malignant biological behavior of these cancers by targeting mutant KRAS. The ornithine decarboxylase/antizyme (ODC/AZ) system is another protein degradation pathway that exists in nature. The formation of an ODC and protein substrate complex through direct combination can promote its degradation by the 26S proteasome without ubiquitination, and this process can be catalyzed by AZ. In this study, we designed and reconstructed a chimeric fusion protein (named RC-ODC). The engineered fusion protein RC-ODC was confirmed to interact with the mutant KRAS oncoprotein in a co-immunoprecipitation assay, and the introduction of both RC-ODC and AZ resulted in degradation of the exogenous and endogenous mutant KRAS oncoprotein at the post-translational level independent of ubiquitination in vitro. Along with a decreased KRAS level, suppression of PANC-1 cell proliferation was detected in vitro and in vivo, and meanwhile downregulation of phosphorylated extracellular signal-regulated kinase 1/2 (ERK1/2) was also observed. Targeted degradation of the KRAS oncoprotein through the ODC/AZ pathway at the post-translational level may reflect a more effective future therapeutic strategy for pancreatic cancer patients. © 2018 The Authors. IUBMB Life published by Wiley Periodicals,Inc. on behalf of International Union of Biochemistry and Molecular Biology, 71(1):57-65, 2019.