The N-Terminal 81-aa Fragment is Critical for UT-A1 Urea Transporter Bioactivity

• Type of Material: Article
• Authors: Haidong Huang, Emory University; Yuan Yang, Emory University; Douglas C Eaton, Emory University; Jeff M Sands, Emory University; Guangping Chen, Emory University
• Language: English
• Date: 2010-06-16
• Publisher: Bentham Open
• Publication Version: Final Published Version
• Copyright Statement: © Chen et al.; Licensee Bentham Open
• License: Creative Commons Attribution-Noncommercial 3.0 Unported
• Final Published Version (URL): http://benthamopen.com/contents/pdf/JEBP/JEBP-3-34.pdf
• Title of Journal or Parent Work: Journal of Epithelial Biology & Pharmacology
• ISSN: 1875-0443
• Volume: 2010
• Issue: 3
• Start Page: 34
• End Page: 39
• Grant/Funding Information: This work was supported by AHA Beginning Grant-In-Aid 0765202B (to G.C), Emory URC grant 255012 (to G.C), and NIH Grants P01-DK61521 (to J.M.S. and D.C.E.), R01-DK41707 (to J.M.S), R37-DK37963 (to D.C.E.).
• Keywords: urea transport; membrane protein; proteolysis; trafficking
• Research Categories: Health Sciences, General; Health Sciences, Pharmacology; Biology, Physiology

Abstract

The serine protease, furin, is involved in the activation of a number of proteins most notably epithelial sodium channels (ENaC). 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 has a consensus furin cleavage site (RSKR) in the N-terminal region. Despite the putative cleavage site, we find that UT-A1, either from the cytosolic or cell surface pool, is not cleaved by furin in CHO cells. This result was further confirmed by an inability of furin to cleave in vitro an 35S-labeled UT-A1 or the 126 N-terminal UT-A1 fragment. Functionally, mutation of the furin site (R78A, R81A) does not affect UT-A1 urea transport activity. However, deletion of the 81-aa N-terminal portion does not affect UT-A1 cell surface trafficking, but seriously impair UT-A1 urea transport activity. Our results indicate that UT-A1 maturation and activation does not require furin-dependent cleavage. The N-terminal 81-aa fragment is required for proper UT-A1 urea transport activity, but its effect is not through changing UT-A1 membrane trafficking.