Human Molecular Genetics Advance Access originally published online on October 22, 2008
Human Molecular Genetics 2009 18(2):267-277; doi:10.1093/hmg/ddn354
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Defective cellular trafficking of missense NPR-B mutants is the major mechanism underlying acromesomelic dysplasia-type Maroteaux
1 Department of Pathology 2 Department of Pediatrics, Faculty of Medicine and Health Sciences, United Arab Emirates University, Al-Ain, United Arab Emirates 3 Molecular Medicine, National Heart and Lung Institute, Imperial College London, London SW7 2AZ, UK 4 Max Delbrück Center for Molecular Medicine, Berlin-Buch, Berlin, Germany 5 Medical Faculty of the Charité, Experimental and Clinical Research Center, Franz-Volhard-Clinic, Berlin, Germany
* To whom correspondence should be addressed at: Department of Pathology, Faculty of Medicine and Health Sciences, UAE University, PO Box 17666, Al-Ain, United Arab Emirates. Tel: +971 37137470; Fax: +971 37671966; Email: bassam.ali{at}uaeu.ac.ae or br_ali{at}hotmail.com
Received July 12, 2008; Revised October 9, 2008; Accepted October 20, 2008
Natriuretic peptides (NPs) comprise a family of structurally related but genetically distinct hormones that regulate a variety of physiological processes such as cardiac growth, blood pressure, axonal pathfinding and endochondral ossification leading to the formation of vertebrae and long bones. The biological actions of NPs are mediated by natriuretic peptide receptors (NPRs) A, B and C that are located on the cell surface. Mutations in NPR-B have been shown to cause acromesomelic dysplasia-type Maroteaux (AMDM), a growth disorder in humans and severe dwarfism in mice. We hypothesized that missense mutations of NPR-B associated with AMDM primarily affect NPR-B function by the arrest of receptor trafficking at the endoplasmic reticulum (ER), due to conformational change, rather than an impairment of ligand binding, transmission of signal through the membrane or catalytic activity. Twelve missense mutations found in AMDM patients and cn/cn mice were generated by site-directed mutagenesis and transiently overexpressed in HeLa cells. Confocal microscopy revealed that 11 out of 12 mutants were retained in the ER. Determination of the ligand-dependent cGMP response confirmed that ER-retained NPR-B mutants are non-functional. Meanwhile, the only cell surface-targeted NPR-B missense mutant (D176E) displayed greatly reduced enzymatic activity due to impaired ligand binding. Thus, in the majority of cases of AMDM associated with missense NPR-B mutation, disease appears to result from defects in the targeting of the ER receptor to the plasma membrane.