UT‐A1 urea transporter activation does not involve furin‐dependent cleavage

Abstract

The serine protease furin is involved in the activation of a number of proteins. The urea transporter UT‐A1, located in the kidney inner medullary collecting duct (IMCD), is important for urine concentrating ability. UT‐A1's amino acid sequence revealed a consensus furin cleavage site (RSKR) in its N‐terminal region. Here, we report that UT‐A1 does not process furin cleavage in furin‐manipulated CHO cells, either in the cytosol or in the biotinylated cell surface pool. This result was further confirmed by in vitro furin digestion of 35S labeled UT‐A1 or a 126 N‐terminal fragment prepared from rabbit reticulocyte lysate translation system. As a positive control, the alpha subunit of the epithelial sodium channel (ENaC) was cleaved twice in vitro by furin. Functionally, mutation of the two key arginine residues in the furin consensus site (R78A, R81A) did not affect UT‐A1 urea transport activity in oocytes and protein cell surface expression. Our results indicate that UT‐A1 maturation and activation does not involve furin‐dependent proteolytic cleavage, and that the consensus furin site (R‐X‐R/K‐R) is required but may not be sufficient for furin digestion.