FIG. 7.

Glypican-1 concentrates FGF-2 in lipid raft microdomains that exclude FGF-2 signaling receptors. (A) WT and C6 myoblasts were incubated with [¹²⁵I]-FGF-2 for 3 h at 4°C and then fractionated as described for Fig. 1. The fractions were analyzed for HSPGs by using anti-stub, as described for Fig. 1A, or exposed to a phosphorimager to detect the distribution of ¹²⁵I-FGF-2. (B) C2C12 myoblasts were fractionated as explained for Fig. 7A. The fractions were analyzed for the distribution of FGFR-I and FGFR-IV as well as membrane distribution markers Cav-1, GM-1, and Na⁺/K⁺ATPase (ATPase). (C) FGF-2 cell surface receptors in C2C12 myoblasts were affinity cross-linked to ¹²⁵I-FGF-2 at 4°C. The cells were lysed and fractionated as explained for Fig. 7A. Aliquots of each fraction were separated on SDS-PAGE (4 to 10%). The gel was dried and exposed to a phosphorimager (upper panel) or analyzed by Western immunoblotting for Cav-1, GM-1, and ATPase. ¹²⁵I-FGF-2-FGFR-I and ¹²⁵I-FGF-2-FGFR-IV correspond to ¹²⁵I-FGF-2 cross-linked to FGFR-I and FGFR-IV, respectively.