FGFR2 ciliary trafficking requires IFT144, BBS1 and GRK2. (A) Schematic presentation of proteins with previously ascribed function in ciliary trafficking of transmembrane receptors. (B) Scheme of the siRNA experiments. (C) Western blot of cells transfected with siRNA, showing downregulation of IFT20, IFT144, RAB23, and ARL6, respectively; actin was used as a loading control and for normalization of densitometry (Fig. S5 A). The effect on cilium frequency and length is in Fig. S5 B. (D)Bbs1 transcript level in cells transfected with Bbs1 siRNA, compared with the scrambled control (siScr, red dashed line), and normalized using Gapdh expression. (E) Effect of siRNA expression on ciliary FGFR2 amounts, obtained after FGFR2 and ARL13B immunocytochemistry. Scale bar, 1 μm. The significance is displayed toward the siScr cells. Total cellular FGFR2 levels are in Fig. S5 C. The effect of siRNA expression on ciliary levels of FGFR1 and FGFR2 in IMCD3, NIH3T3, and 3T3-L1 cells is in Fig. S5, E–J. (F) Effect of GRK2 inhibitors CMPD101 (10 µM) and paroxetine (2 µM) on ciliary FGFR2 amounts, after serum starvation in the presence of the respective inhibitors. Scale bar, 1 μm. The significance is displayed toward the non-treated cells. The total cellular FGFR2 levels are in Fig. S5 D. Statistical significances were calculated using Welch’s t test (P < 0.05; **P < 0.01, ***P < 0.001); n.s., not significant. Bar plot—mean ± SEM. Box and whiskers—min-max 10–90%. The n value indicates the number of independent experiments; the number of analyzed cilia is shown directly in the graphs. Source data are available for this figure: SourceData F6.