CUBN and diabetes mellitus: 2007; Dronavalli et al. 2008; Tang et al. 2011). To provide insight into the tubular mechanisms underlying DN, transferrin excretion in urine was analyzed in DM and CTRL animals. Transferrin is a 75‐kDa protein that is ultrafiltered by the glomerulus and largely reabsorbed by proximal tubule via receptor‐mediated endocytosis. Transferrin binds to its receptor cubilin to be endocytosed (Kozyraki et al. 2001; Jeong et al. 2014).