Fig. 9. Megalin mediates binding and cellular catabolism of BMP4. (A) Surface plasmon resonance (SPR) analysis of binding of 0.5 µmol/l BMP4 but not of 0.5 µmol/l BMP5 or WNT1-conditioned medium to purified megalin immobilized on the sensor chip surface (see Materials and methods for details). As a positive control, binding of 1 µmol/l receptor-associated protein (RAP) to megalin was tested. (B) Megalin-expressing BN16 cells mediate uptake and lysosomal degradation of ¹²⁵I-BMP4. Degradation of BMP4 can be blocked by chloroquine (200 µmol/l) or the receptor-antagonist RAP (100 µg/ml).