The degron sequence of ornithine decarboxylase (ODC) is recognized directly by proteasomes, which leads to the destruction of the involved protein. The retroviral expression vector pQCXIN-ZsGreen-cODC, containing green fluorescence ZsGreen-labeled degron ODC (Gdeg) was kindly provided by Dr Frank Pajonk (Jonsson Comprehensive Cancer Center, UCLA, CA, USA). The plasmid was transfected into Platinum retroviral packaging cells using Lipofectamine® 2000 (Thermo Fisher Scientific, Inc.). The plasmid and Lipofectamine® 2000 were diluted with Opti-MEM I reduced serum medium (Thermo Fisher Scientific, Inc.) for 5 min at room temperature, separately. The diluted Lipofectamine® 2000 was subsequently mixed with the diluted plasmid and incubated for 15 min at room temperature. The mixture was then added to cells immediately at room temperature, after which the cells were incubated at 37°C. And the retrovirus collected from the supernatant was used for Panc-1 cell infection as previously described (32 (link)-34 (link)). Stable transfectants were selected with G418 solution (Sigma-Aldrich; Merck KGaA) and maintained in 0.1 mg/ml G418 solution.