Degradation mechanism of a Golgi-retained distal tubular acidosis mutant of the kidney Anion Exchanger 1 in renal cells

Abstract

Distal renal tubular acidosis (dRTA) is a renal disease caused in some cases by mutations in the SLC4A1 gene encoding the kidney anion exchanger 1 (kAE1). Both recessive and dominant mutations result in mis-trafficking of proteins, preventing them from reaching the basolateral membrane of renal epithelial cells where their function is needed. kAE1 G701D is a functional, Golgi-retained dRTA mutant. The purpose of this thesis is to understand the degradation pathways of kAE1 G701D. We show that this mutant is poly-ubiquitylated and degraded by both lysosomal and proteasomal pathways. We provide evidence that the Nedd4 family interacting protein 1 (Ndfip1) interacts with kAE1 G701D, suggesting a possible role of Ndfip1 in the ubiquitylation process of this mutant. Also, we show that this mutant reaches temporarily the cell surface where it is endocytosed and degraded by the lysosomes via a peripheral quality-control machinery dependent mechanism. Furthermore we show that the function of kAE1 G701D is rescued at the cell surface upon inhibition of the lysosome and incubation with the chemical chaperone dimethyl sulfoxide (DMSO). This study suggests that modulating the peripheral quality-control machinery may provide novel therapeutic strategies for the treatment of dRTA patients.