Human Molecular Genetics Advance Access published online on July 21, 2008
Human Molecular Genetics, doi:10.1093/hmg/ddn214
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FAILURE OF BONE MORPHOGENETIC PROTEIN RECEPTOR TRAFFICKING IN PULMONARY ARTERIAL HYPERTENSION: POTENTIAL FOR RESCUE
1 From Department of Medicine, University of Cambridge School of Clinical Medicine, Box 157, Addenbrooke's Hospital, Hills Road, Cambridge, Cambridgeshire, CB2 2QQ, UK 2 Kings College London, Strand, London WC2R 2LS, UK
* Address correspondence to: Nicholas W. Morrell, Department of Medicine, University of Cambridge School of Clinical Medicine, Box 157, Addenbrooke's Hospital, Hills Road, Cambridge, Cambridgeshire, CB2 2QQ. UK. Telephone: 44 1223 762007 Fax: 44 1223 762007:E-mail: nwm23{at}cam.ac.uk
Received June 3, 2008; Revised July 19, 2008; Accepted July 19, 2008
Heterozygous germline mutations in the gene encoding the bone morphogenetic protein type II receptor cause familial pulmonary arterial hypertension. We previously demonstrated that substitution of cysteine residues in the ligand binding domain of this receptor prevent receptor trafficking to the cell membrane. Here we demonstrate the potential for chemical chaperones to rescue cell surface expression of mutant BMPR-II and restore function. HeLa cells were transiently transfected with BMPR-II wild type or mutant (C118W) receptor constructs. Immunolocalisation studies confirmed retention of the cysteine mutant receptor mainly in the endoplasmic reticulum. Co-immunoprecipitation studies of Myc-tagged BMPR-II confirmed that the cysteine-substituted ligand binding domain mutation, C118W, is able to associate with BMP type I receptors. Furthermore, following treatment with a panel of chemical chaperones (thapsigargin, glycerol or sodium 4-phenylbutyrate) we demonstrated a marked increase in cell surface expression of mutant C118W BMPR-II by FACS analysis and confocal microscopy. These agents also enhanced the trafficking of wild type BMPR-II, though to a lesser extent. Increased cell surface expression of mutant C118W BMPR-II was associated with enhanced Smad1/5 phosphorylation in response to BMPs. These findings demonstrate the potential for rescue of mutant BMPR-II function from the endoplasmic reticulum. For the C118W mutation in the ligand binding domain of BMPR-II, cell surface rescue leads to at least partial restoration of BMP signalling. We conclude that enhancement of cell surface trafficking of mutant and wild type BMPR-II may have therapeutic potential in familial pulmonary arterial hypertension.
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