Functional consequences of USP18-mediated interference with ternary complex assembly. (a and b) Western blot analysis of STAT1 and STAT2 phosphorylation in parental HLLR1 cells versus cells stably expressing USP18 (HU13) stimulated with IFNα2-wt, -R120A, or -M148A. (c and d) Dose–response curve for pSTAT normalized to total STAT calculated from the band intensities in the Western blot (representative data from three independent experiments). Values were normalized to those obtained at the highest dose of IFN wt, which was taken as 100%. The broken lines represent the curve extrapolations for lower IFN doses expected from independent experiments.