Figure 2.

FGFRs partly comigrate with caveolin. (A) COS cells were homogenized in sodium carbonate, sonicated, and fractionated by floating in a sucrose density gradient. The protein content of each fraction is expressed as a percentage of the total amount of protein in the gradient. (B) Aliquots of the fractions in A were analyzed by SDS-PAGE and Western blotting with anti-caveolin, anti-clathrin, and anti-transferrin receptor antibodies. (C) COS cells transfected with FGFR4 were incubated with ¹²⁵I-aFGF for 3 h at 4°C and treated for 20 min at 4°C with 0.3 mM disuccinimidyl suberate to cross-link the bound growth factor to the receptors. Then the cells were homogenized, sonicated, and fractionated as described above. The fractions were analyzed by SDS-PAGE and autoradiography. COS cells transfected with FGFR4 (D) and CPAE cells (E) were treated and fractionated as described above. The fractions were analyzed by Western blotting with anti-FGFR4 (D) or anti-FGFR1 and anti-caveolin (E).