Inhibition of GrB by RNAi in MCF-7 cells reduced nuclear FGFR1 accumulation. (A) Schematic representation of FGFR1 depicting the three IgG loops of the extracellular domain, the transmembrane region (TM), and the split tyrosine kinase domain. The arrow indicates GrB cleavage site at Asp-432. Numbers indicate amino acid residues. Adapted from Loeb et al. (2006). N, N terminus; C, C terminus. (B) Treatment of MCF-7 cells, growing in serum-containing medium, with a GrB inhibitor abolished nuclear FGFR1 after 24 h but did not change the total FGFR1 protein levels. Confocal analysis of MCF-7 cells growing in serum-containing medium treated with GrB RNAi for 72 h revealed efficient knockdown of GrB concomitant with decreased nuclear FGFR1 staining. **, P < 0.01; ***, P < 0.001 (Student’s t test). Bar, 25 µm. (C) Western blot analysis confirmed that GrB was expressed in MCF-7 cells and showed that 72-h treatment with RNAi to GrB reduced levels of nuclear FGFR1, despite an overall increase in full-length FGFR1. *, P < 0.05; **, P < 0.01 (Mann–Whitney test). Error bars show means ± SEM. A.U., arbitrary unit; Ctr, control.