The transferrin receptor in hepatocyte nodules: binding properties, subcellular distribution and endocytosis

Transferrin binding was found to be around 60-fold higher in hepatocyte nodules compared to normal liver, with no apparent differences in binding affinity or molecular weight of binding proteins, indicating that the increase in [125I]transferrin binding was the result of an increased number of binding sites with similar properties as in normal liver. The relative 'induction' of transferrin receptors was most marked in the total membrane fraction followed by membrane subfractions comprising endoplasmic reticulum, the Golgi complex and endocytic vesicles. Despite the increased number of transferrin receptors, the in vivo endocytosis of transferrin, measured as uptake of [125I]ferrotransferrin, was quantitatively similar in nodular cells compared to normal liver. The number of transferrin receptors in regenerating liver, 48 h after partial hepatectomy, was increased 20-fold over normal levels, but binding affinity, receptor structure and kinetics of transferrin uptake were normal. A slower than normal rate of 59Fe accumulation in hepatocyte nodules may suggest an alteration in the dissociation of iron from ferrotransferrin, thereby suggesting one mechanism relevant to the iron storage deficiency in nodular cells.