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

Paul B Yu,Hideyuki Beppu,Noriko Kawai,En Li,Kenneth D Bloch

doi:10.1074/jbc.m502825200

Paul B Yu, Hideyuki Beppu + Show 3 more

Open Access

https://doi.org/10.1074/jbc.m502825200

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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.

Highlights

Bone morphogenetic protein (BMP)1 signals regulate embryonic tissue patterning and organogenesis, as well as the remodeling of mature tissues [1]
RNA extracted from Bmpr2del/del cells was amplified by RT-PCR with primers specific for sequences in exons 3 and 8, and the product was sequenced to reveal direct splicing of exon 3 to exon 6, with stop codons in exon 6 resulting from a frameshift [35]
Because conventional gene targeting of both Bmpr2 alleles in mice results in embryonic lethality [33], both Bmpr2 alleles were disrupted in pulmonary arterial smooth muscle cells (PASMC) ex vivo using the Cre-lox system

Summary

Introduction

Bone morphogenetic protein (BMP) signals regulate embryonic tissue patterning and organogenesis, as well as the remodeling of mature tissues [1]. Three type II receptors, BMPR2 and the activin type II receptors ActRIIa and ActRIIb [12,13,14,15,16,17], 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]. In BMPR2deficient cells, BMP signals were transduced by receptor complexes consisting of the ActRIIa receptor and a set of type I co-receptors distinct from those utilized by BMPR2, resulting in the gain of signaling for certain BMP ligands

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