USP18 promotes pancreatic tumour growth in vivo and in vitro. (A, B) USP18 mRNA and protein levels in pancreatic cells and the immortalized H6C7 line. (C and D) USP18 protein levels in BxPC-3 and SW1990 cells after transfection with shUSP18 or p-USP18. (E) CCK-8 assay showing proliferation of pancreatic cancer cells following USP18 knockdown. *p<0.05. (F) Proliferation capacities were detected by EdU assays in BxPC-3 cells transfected with the shNC or the shUSP18 plasmid *p<0.05. (G and H) CCK-8 and EdU assay showing proliferation of pancreatic cancer cells transfected with the vector or the p-USP18 plasmid. (I and J) Colony-forming assays showing the cell viability of pancreatic cancer cells transfected with the indicated plasmid (*p<0.05, **p<0.01). (K–N) BxPC-3/shUSP18 cells or SW1990/p-USP18 were subcutaneously injected into nude mice. Tumour volumes were measured on the indicated days. At the experimental endpoint, tumours were dissected, photographed and weighed (n=15, *p<0.05).