Bone Morphogenetic Protein (BMP) Type II Receptor Deletion Reveals BMP Ligand-specific Gain of Signaling in Pulmonary Artery Smooth Muscle Cells

Abstract

Bone morphogenetic protein (BMP) ligands signal by binding the BMP type II receptor (BMPR2) or the activin type II receptors (ActRIIa and ActRIIb) in conjunction with type I receptors to activate SMADs 1, 5, and 8, as well as members of the mitogen-activated protein kinase family. Loss-of-function mutations in Bmpr2 have been implicated in tumorigenesis and in the etiology of primary pulmonary hypertension. Because several different type II receptors are known to recognize BMP ligands, the specific contribution of BMPR2 to BMP signaling is not defined. Here we report that the ablation of Bmpr2 in pulmonary artery smooth muscle cells, using an ex vivo conditional knock-out (Cre-lox) approach, as well as small interfering RNA specific for Bmpr2, does not abolish BMP signaling. Disruption of Bmpr2 leads to diminished signaling by BMP2 and BMP4 and augmented signaling by BMP6 and BMP7. Using small interfering RNAs to inhibit the expression of other BMP receptors, we found that wild-type cells transduce BMP signals via BMPR2, whereas BMPR2-deficient cells transduce BMP signals via ActRIIa in conjunction with a set of type I receptors distinct from those utilized by BMPR2. These findings suggest that disruption of Bmpr2 leads to the net gain of signaling by some, but not all, BMP ligands via the activation of ActRIIa. Bone morphogenetic protein (BMP)1 signals regulate embryonic tissue patterning and organogenesis, as well as the remodeling of mature tissues (1). BMPs, like other transforming growth factor ␤ superfamily ligands, induce apposition of type I and type II receptors to cause phosphorylation of type I receptors. Activated BMP type I receptors phosphorylate the BMP-responsive SMAD proteins 1, 5, and 8, leading to their nuclear translocation and the regulation of target gene transcription. The Id (inhibitor of differentiation) gene family is an important target of BMP signals (2-5), serving to regulate the differentiation and proliferation of a variety of mature and embryonic cell lineages, including vascular smooth muscle and endothelium (2, 6 -8). BMP ligands may also trigger the activation of MAP kinases via SMAD-independent signaling pathways (9 -11).Three type II receptors, BMPR2 and the activin type II receptors ActRIIa and ActRIIb (12-17), can pair with three different type I receptors, ActRIa/ALK2, BMPRIa/ALK3, and BMPRIb/ALK6 (13, 18 -23), to transduce BMP signals. These various BMP receptors have distinct temporal and spatial expression in tissues and have varying affinities for each of more than 15 known BMP molecules (1, 24). Although BMPR2, ActRIIa, and ActRIIb can each bind BMP ligands (12-15, 21, 22, 25), the preferred ligand-receptor complexes used by cells for BMP signaling are not known.In this study, we examined the signaling mediated by two structurally distinct classes of BMP ligands that are known to be expressed in vascular smooth muscle and endothelial cells and that regulate their function (6, 26 -30). The first class of BMP ligands includes the 92% homologous BMP2 and BMP4, considere...

Nodal·Gdf1 Heterodimers with Bound Prodomains Enable Serum-independent Nodal Signaling and Endoderm Differentiation

“…In keeping with this result, deletion of Bmpr2 in early mouse embryos leads to increased pSmad2 activation by Acvr2b (42). These observations are compatible with a potential role for Bmpr2 as a decoy receptor of Acvr2 ligands as described in pulmonary smooth muscle cells (53). However, they do not explain why soluble Acvr2 selectively inhibits Nodal⅐Gdf1 but not Nodal.…”

Novel promoter and exon mutations of the BMPR2 gene in Chinese patients with pulmonary arterial hypertension

“…8 -10 All the defects of BMPR2 gene identified in patients, which include all major mutation classes, with single nucleotide substitutions resulting in nonsense, 6 33 -35 Earlier studies have shown that BMPR2 mutations lead to a loss of signaling through Smad1/5 in cells and animal models. 25,36 Thus, failure of BMP signaling through Smad1/5 in the vasculature can increase TGF-b/Smad2/3 signaling, which highlights the potential importance of a loss of Smad1/5 signaling as cause of pulmonary vascular remodeling in patients with genetic PAH. In our study, the mutation À669A in the promoter sequence of BMPR2 gene showed decreased transcriptional activity and may downregulate the expression of BMPR2 and weaken Smad1/5 signaling, similarly to BMPR2 coding region mutations.…”

Exon-based mapping of microarray probes: Recovering differential gene expression signal in underpowered hypoxia experiment

“…The biological relevance of 4 newly identified genes to hypoxia and pulmonary hypertension was suggested by an automated biomedical literature search. The subsequent manual evaluation of PubMatrix citations confirmed involvement of Mig6, F3, Bmp6, and Ndrg1 genes in hypoxia-triggered response [15][16][17][18][19]. Up-regulation of Mig6 expression was validated by real-time RT-PCR.…”

“…Transcriptional changes detected by 26 exon-sharing probe-sets ( Figure 1B) were compared to those detected by the rest of the target-sharing probe-sets (63 probe-sets, Figure 1C) and demonstrated higher correlation of transcriptional changes detected by the exon-sharing probe-sets. The PubMatrix automated biomedical literature search of 24 recovered ( Figure 1A) candidate genes identified several well-known hypoxia or pulmonary hypertension-related genes (Table 1), including Mig6, F3, Bmp6, and Ndrg1 [15][16][17][18][19]. The mouse Mig6 gene was selected for further validation.…”