Human Molecular Genetics Advance Access originally published online on March 4, 2008
Human Molecular Genetics 2008 17(11):1683-1694; doi:10.1093/hmg/ddn059
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Stoichiometric imbalance in the receptor complex contributes to dysfunctional BMPR-II mediated signalling in pulmonary arterial hypertension
1 Department of Medical and Molecular Genetics, King’s College London, Guy’s Hospital, London SE1 9RT, UK 2 Department of Genetics, University of Leicester, Leicester LE1 7RH, UK 3 Department of Medicine, University of Cambridge, Cambridge, UK
* To whom correspondence should be addressed. Tel: +44 2071889505; Fax: +44 2071882585; Email: talat.nasim{at}genetics.kcl.ac.uk (T.N.); Tel: +44 2071887994; Fax: +44 2071888050; Email: richard.trembath{at}genetics.kcl.ac.uk (R.C.T.)
Received December 21, 2007; Accepted February 22, 2008
Heterozygous germline defects in a gene encoding a type II receptor for bone morphogenetic proteins (BMPR-II) underlie the majority of inherited cases of the vascular disorder known as pulmonary arterial hypertension (PAH). However, the precise molecular consequences of PAH causing mutations on the function of the receptor complex remain unclear. We employed novel enzymatic and fluorescence activity based techniques to assess the impact of PAH mutations on pre-mRNA splicing, nonsense-mediated decay (NMD) and receptor complex interactions. We demonstrate that nonsense and frameshift mutations trigger NMD, providing further evidence that haplo-insufficiency is a major molecular consequence of disease-related BMPR2 mutations. We identified heterogeneous functional defects in BMPR-II activity, including impaired type I receptor phosphorylation, receptor interactions and altered receptor complex stoichiometry leading to perturbation of downstream signalling pathways. Importantly, these studies demonstrate that the intracellular domain of BMPR-II is both necessary and sufficient for receptor complex interaction. Finally and to address the potential for resolution of stoichiometric balance, we investigated an agent that promotes translational readthrough of a BMPR2 nonsense reporter construct without interfering with the NMD pathway. We propose that stoichiometric imbalance, due to either haplo-insufficiency or loss of optimal receptor–receptor interactions impairs BMPR-II mediated signalling in PAH. Taken together, these studies have identified an important target for early therapeutic intervention in familial PAH.