Abstract
Natriuretic peptide receptor A (NPR-A/GC-A) and B (NPR-B/GC-B) are members of the transmembrane guanylyl cyclase family that mediate the effects of natriuretic peptides via the second messenger, cGMP. Despite numerous reports of these receptors being down-regulated in response to various pathological conditions, no studies have actually measured desensitization and receptor internalization in the same cell line. Furthermore, the ligand-dependent trafficking properties of NPR-A remain controversial, whereas nothing is known about the trafficking of NPR-B. In this report, we tested whether down-regulation explains the ligand-dependent desensitization of NPR-A and NPR-B and characterized their trafficking properties using a combination of hormone-binding and antibody-based assays. Quantitative partition analysis indicated that 125I-atrial natriuretic peptide (ANP) was rapidly released into the medium after 293T cells stably expressing NPR-A were warmed from 4° to 37°C. High-performance liquid chromatography fractionation of medium supplemented with the protease inhibitor phosphoramidon indicated that the 125I-ANP was mostly intact. In contrast, 125I-ANP purified from medium bathing cells expressing NPR-C, a receptor known to internalize natriuretic peptides, was degraded. Cleavable biotinylation and noncleavable biotinylation assays indicated that neither NPR-A nor NPR-B was internalized or degraded in response to natriuretic peptide binding. In contrast, agonist-dependent internalization of a G protein-coupled receptor was clearly apparent in the same cell line. Finally, we show that NPR-A and NPR-B are desensitized in cells in which they are not internalized. We suggest that mechanisms other than receptor down-regulation account for the desensitization of NPR-A and NPR-B that occurs in response to various physiological and pathological stimuli.
- Received May 6, 2004.
- Accepted September 20, 2004.
- The American Society for Pharmacology and Experimental Therapeutics
MolPharm articles become freely available 12 months after publication, and remain freely available for 5 years.Non-open access articles that fall outside this five year window are available only to institutional subscribers and current ASPET members, or through the article purchase feature at the bottom of the page.
|