Bone morphogenetic protein type II receptor mutations causing protein misfolding in heritable pulmonary arterial hypertension.

More than 70% of cases of heritable pulmonary arterial hypertension are due to heterozygous germline mutations in the gene encoding the bone morphogenetic protein type II receptor (BMPR-II), a receptor for the transforming growth factor-β/BMP superfamily. Among the many mutations identified, some involve substitution of cysteine residues in the ligand-binding domain or the kinase domains of BMPR-II. These mutants are characterized by retention within the endoplasmic reticulum. This retention causes loss of function in terms of phosphorylation of downstream Smad1, Smad5, and Smad8 and the transcription of BMP target genes. The retention has a dominant negative effect on BMP signaling because it also impairs trafficking of the associated type I receptor. Studies suggest a more severe phenotype in patients with this class of mutation. We have shown that trafficking of cysteine-substituted mutants can be partially restored in the presence of chemical chaperones. Restoration of cell surface expression of ligand-binding domain mutants leads to partial rescue of BMP signaling and suggests that small-molecule pharmacological chaperones may be a therapeutic option in these patients.