Pathophysiology of cubilin: of rats, dogs and men

At variance from small solutes which are reabsorbed by transporters and channels, proteins present in the proximal convoluted tubule lumen are internalized by endocytosis via a vesicular system, transferred to the lysosomes and degraded. We summarize here recent data on cubilin, a 460 kDa peripheral protein which, together with megalin, serves as a multiligand receptor providing for the reabsorption of most proteins present in the tubule lumen. Interestingly, cubilin is also expressed by the yolk sac, which has endocytic and degradative properties reminiscent of the proximal tubule and serves as the receptor for intrinsic factor-vitamin B12 complexes.