Fig. 5. Both endocrine and paracrine FGFs signal via asymmetric receptor dimers.

a, Schematic diagram showing that, in response to FGF23 and αKlotho cotreatment, FGFR1c^ΔSLBS and FGFR1c^ΔPLBS can complement each other and form a 1:1:1:1:1 FGF23–FGFR1c^ΔSLBS–FGFR1c^ΔPLB–αKlotho–HS asymmetric complex. b, Immunoblot analyses of whole extracts from untreated or FGF23- and αKlotho-cotreated L6 cell lines singly expressing FGFR1c^WT, FGFR1c^ΔPLBS and FGFR1c^ΔSLBS or co-expressing FGFR1c^ΔSLBS with FGFR1c^ΔPLBS probed as in Fig. 2. c, Schematic diagram showing that FGF23, αKlotho and FGFR4^ΔSLBS (serving as a primary receptor) form a ternary complex and recruit FGFR1c^ΔPLBS as a secondary receptor, in the presence of HS. d, FGF23- and αKlotho-cotreated L6 cell lines stably expressing FGFR4^WT, FGFR4^ΔSLBS alone or FGFR4^ΔSLBS together with FGFR1c^ΔPLBS were analysed for FGFR activation/signalling using western blotting of total cell lysates as in Fig. 2. e, Schematic diagram showing that, in response to paracrine FGF1/4 and HS, FGFR1c^ΔSLBS and FGFR1c^ΔPLBS can complement each other and form 1:1:1:1 FGF–FGFR1c^ΔSLBS–FGFR1c^ΔPLBS–HS asymmetric signalling complexes. f, L6 cell lines expressing FGFR1c^ΔSLBS and FGFR1c^ΔPLBS individually or co-expressing them were treated with FGF1 (1 nM) and cell extracts were immunoblotted as in Fig. 2. g, Schematic diagram showing that FGF1, HS and FGFR4^ΔSLBS (serving as primary receptor) form a stable complex which subsequently recruits FGFR1c^ΔPLBS as a secondary receptor. h, L6 cell lines expressing FGFR4^WT or FGFR4^ΔSLBS singly or co-expressing FGFR4^ΔSLBS with FGFR1c^ΔPLBS were treated with FGF1 (1 nM) and cell extracts were immunoblotted as in Fig. 2. Experiments were performed in biological triplicates with similar results. CT, C terminus; NT, N terminus.