Functional interaction between BMPR-II and Tctex-1, a light chain of Dynein, is isoform-specific and disrupted by mutations underlying primary pulmonary hypertension

Diverse heterozygous mutations of bone morphogenetic receptor type II (BMPR-II) underlie the inherited form of the vascular disorder primary pulmonary hypertension (PPH). As yet, the molecular detail of how such defects contribute to the pathogenesis of PPH remains unclear. BMPR-II is a member of the transforming growth factor-beta cell signalling superfamily. Ligand binding induces cell surface receptor complex formation and activates a cascade of phosphorylation events of intracellular intermediaries termed Smads, which initiate transcriptional regulation. Some 30% of PPH-causing mutations localize to exon 12, which may be spliced out forming an isoform depleted of the unusually long BMPR-II cytoplasmic tail. To further elucidate the consequences of BMPR2 mutation, we sought to characterize aspects of the cytoplasmic domain function by seeking intracellular binding partners. We now report that Tctex-1, a light chain of the motor complex dynein, interacts with the cytoplasmic domain of BMPR-II and demonstrate that Tctex-1 is phosphorylated by BMPR-II, a function disrupted by PPH disease causing mutations within exon 12. Finally we show that BMPR-II and Tctex-1 co-localize to endothelium and smooth muscle within the media of pulmonary arterioles, key sites of vascular remodelling in PPH. Taken together, these data demonstrate a discrete function for the cytoplasmic domain of BMPR-II and justify further investigation of whether the interaction with and phosphorylation of Tctex-1 contributes to the pathogenesis of PPH.