Receptor for activated C-kinase 1, a novel interaction partner of type II bone morphogenetic protein receptor, regulates smooth muscle cell proliferation in pulmonary arterial hypertension.
BACKGROUND
Pulmonary arterial hypertension (PAH) is characterized by selective elevation of pulmonary arterial pressure. The pathological hallmark of PAH is the narrowing of pulmonary arterioles secondary to endothelial cell dysfunction and smooth muscle cell proliferation. Heterozygous mutations in BMPR2, encoding the type II bone morphogenetic protein receptor (BMPRII), were identified in PAH, suggesting that alterations to BMPRII function are involved in disease onset and/or progression.


RESULTS
We identified the receptor for activated C-kinase (RACK1) as a novel interaction partner of BMPRII by yeast 2-hybrid analyses using the kinase domain of BMPRII as a bait. Glutathione-S-transferase pull-down and coimmunoprecipitation confirmed the interaction of RACK1 with BMPRII in vitro and in vivo. RACK1-BMPRII interaction was reduced when kinase domain mutations occurring in patients with PAH were introduced to BMPRII. Immunohistochemistry of lung sections from PAH and control patients and immunofluorescence analysis of primary pulmonary arterial smooth muscle cells demonstrated colocalization of BMPRII and RACK1 in vivo. Quantitative reverse-transcription polymerase chain reaction and Western blot analysis showed significant downregulation of RACK1 expression in the rat model of monocrotaline-induced PAH but not in pulmonary arterial smooth muscle cells from PAH patients. Abrogation of RACK1 expression in pulmonary arterial smooth muscle cells led to decreased Smad1 phosphorylation and increased proliferation, whereas overexpression of RACK1 led to increased Smad1 phosphorylation and decreased proliferation.


CONCLUSIONS
RACK1, a novel interaction partner of BMPRII, constitutes a new negative regulator of pulmonary arterial smooth muscle cell proliferation, suggesting a potential role for RACK1 in the pathogenesis of PAH.
Zakrzewicz
Anna
A
University of Giessen Lung Center, Department of Medicine II, Justus Liebig University Giessen, D-35392 Giessen, Germany.
Hecker
Matthias
M
Marsh
Leigh M
LM
Kwapiszewska
Grazyna
G
Nejman
Bozena
B
Long
Lu
L
Seeger
Werner
W
Schermuly
Ralph T
RT
Morrell
Nicholas W
NW
Morty
Rory E
RE
Eickelberg
Oliver
O
D000328:Adult; D000818:Animals; D052006:Bone Morphogenetic Protein Receptors, Type II / Q000235:genetics / Q000378:metabolism*; D049109:Cell Proliferation; D015536:Down-Regulation / Q000235:genetics; D005260:Female; D019204:GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D006801:Humans; D006976:Hypertension, Pulmonary / Q000473:pathology*; D008297:Male; D051379:Mice; D008875:Middle Aged; D009131:Muscle, Smooth, Vascular / Q000166:cytology; D009154:Mutation; D032389:Myocytes, Smooth Muscle / Q000473:pathology*; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D011485:Protein Binding; D051381:Rats; D000075370:Receptors for Activated C Kinase; D011956:Receptors, Cell Surface / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D051898:Smad1 Protein / Q000378:metabolism; D020798:Two-Hybrid System Techniques
D009363:Neoplasm Proteins; C419368:RACK1 protein, human; D000075370:Receptors for Activated C Kinase; D011956:Receptors, Cell Surface; D051898:Smad1 Protein; D052006:Bone Morphogenetic Protein Receptors, Type II; D019204:GTP-Binding Proteins