From bowel to kidneys: the role of cubilin in physiology and disease.

Cubilin is a large endocytic receptor serving such diverse functions as the intestinal absorption of the intrinsic factor-B(12) complex and the renal proximal tubule reabsorption of filtered proteins including albumin, transferrin, vitamin D-binding protein and other important plasma carriers. Cubilin is a structurally unique, peripheral membrane protein, which depends on the membrane protein amnionless (AMN) for correct apical translocation. In addition, AMN appears important for efficient internalization of intrinsic factor-B(12) in the intestine, whereas in the proximal tubule cubilin interacts with another endocytic receptor, megalin, for effective reabsorption. The importance of cubilin has been demonstrated in several animal models of cubilin deficiency as well as in a variety of human diseases. Recent demonstration of cubilin in podocytes from various species awaits further clarification with respect to the functional role as well as its role in pathology.