CUBAM · Characterization of novel proteins interacting with cubilin and their role in proximal tubular endocytosis

Final Activity Report Summary - CUBAM (Characterization of novel proteins interacting with cubilin and their role in proximal tubular endocytosis)

Uptake of protein in the kidney has been long recognised as a process facilitating their delivery to the lysosomes (digestive apparatus) of kidney cells for degradation to amino acids, which can be subsequently reused for new protein synthesis. From studies over the past decade it has become evident that this process not only facilitates retrieval of proteins, but more importantly, the uptake of other vital substances serving important functions in the kidney and other organs such as vitamins, iron and calcium. On the other hand, involvement of this process in the progression of various renal diseases to terminal failure requiring dialysis and / or transplantation, has been demonstrated or may be anticipated. Interference with this process is a yet unexplored field that requires a detailed knowledge of the molecular components involved. Two receptors megalin and cubilin appear to be largely responsible for this process, but recent data suggested that a protein called amnionless may serve also important function. In this study we aimed at elucidation of new aspects in this field, in particular a specific function of cubilin and a link between cubilin and amnionless in this process. We have developed and exploited several models to gain better insight in this issue. From studies on cubilin-amnionless transfected kidney cells we have learned that amnionless protein assists cubilin through the cell synthetic pathway and is indispensable for its proper localisation in the kidney cells, and thus for cubilin function. Generation of mice deficient with cubilin yielded a long time awaited confirmation of its crucial role in albumin reabsorption. The meaning of this finding was further enhanced by studies on double cubilin and megalin knockout mice. Investigations using these models provided also the evidence that there are other alternative mechanisms of protein uptake, especially regarding apolipoprotein A-1 and transferrin. We have also developed new tools required to progress in this field including novel recombinant expression systems and purification methods for proteins. The intimate knowledge of the molecular interactions involved in the endocytic process gained from the present study is essential for the development of new therapeutic approaches in nephrology that involve modulation of cubilin and megalin expression / function in order to prevent or attenuate kidney uptake of deleterious substances. The cubilin deficient mice will be a useful model to analyse directly the role of albumin trafficking in pathology.

Data: CORDIS, © European Union