Mice lacking the Raf-1 kinase inhibitor protein exhibit exaggerated hypoxia-induced pulmonary hypertension

• Published in: British journal of pharmacology Vol. 163; no. 5; pp. 948 - 963
• Main Authors: MORECROFT, I, DOYLE, B, NILSEN, M, KOLCH, W, MAIR, K, MACLEAN, M. R
• Format: Journal Article
• Language: English
• Published: Basingstoke Nature Publishing Group 01.07.2011; Blackwell Publishing Ltd; Blackwell Science Inc
• Subjects: Animals; Biological and medical sciences; Blotting, Western; Cell Line; Cell Proliferation; Chronic Disease; Cricetinae; Cricetulus; Fibroblasts - enzymology; Fibroblasts - pathology; Gene Deletion; Hypertension; Hypertension, Pulmonary - enzymology; Hypertension, Pulmonary - etiology; Hypoxia; Hypoxia - complications; Hypoxia - enzymology; Immunohistochemistry; Kinases; Lung - enzymology; Lung - pathology; Medical sciences; Mice; Mice, Inbred C57BL; Mice, Knockout; Mitogen-Activated Protein Kinase 1 - biosynthesis; Pharmacology. Drug treatments; Phosphatidylethanolamine Binding Protein - deficiency; Phosphatidylethanolamine Binding Protein - genetics; Phosphorylation; Pneumology; Proteins; Proto-Oncogene Proteins c-raf - antagonists & inhibitors; Pulmonary arteries; Pulmonary hypertension. Acute cor pulmonale. Pulmonary embolism. Pulmonary vascular diseases; Research Papers; Rodents; Up-Regulation; Veins & arteries; 5-HT2A serotonin receptor; Protein inhibitor; Oxygen; 5-HT transporter; Serotonin; Enzyme; Respiratory disease; Transferases; Non-specific serine/threonine protein kinase; RKIP; Rodentia; Cardiovascular disease; Pulmonary hypertension; Vertebrata; Mammalia; receptor; Mouse; Animal; Neurotransmitter; Hypoxia; 5-HT; Carrier protein
• ISSN: 0007-1188; 1476-5381
• DOI: 10.1111/j.1476-5381.2011.01305.x

Increased pulmonary vascular remodelling, pulmonary arterial pressure and pulmonary vascular resistance characterize the development of pulmonary arterial hypertension (PAH). Activation of the Raf/mitogen-activated protein kinase/extracellular signal-regulated kinase (ERK)1/2 is thought to play an important role in PAH and Raf-1 kinase inhibitor protein (RKIP), negatively regulates this pathway. This study investigated whether genetic deletion of RKIP (and hence ERK1/2 up-regulation) resulted in a pulmonary hypertensive phenotype in mice and investigated a role for RKIP in mitogen-regulated proliferative responses in lung fibroblasts. Pulmonary vascular haemodynamics and remodelling were assessed in mice genetically deficient in RKIP (RKIP-/-) after 2 weeks of either normoxia or hypoxia. Immunoblotting and immunohistochemistry were used to examine phosphorylation of Raf-1, RKIP and ERK1/2 in mouse pulmonary arteries. In vitro, RKIP inhibition of mitogen signalling was analysed in CCL39 hamster lung fibroblasts. RKIP-/- mice demonstrated elevated indices of PAH and ERK1/2 phosphorylation compared with wild-type (WT) mice. Hypoxic RKIP-/- mice exhibited exaggerated PAH indices. Hypoxia increased phosphorylation of Raf-1, RKIP and ERK1/2 in WT mouse pulmonary arteries and Raf-1 phosphorylation in RKIP-/- mouse pulmonary arteries. In CCL39 cells, inhibition of RKIP potentiated mitogen-induced proliferation and phosphorylation of RKIP, and Raf-1. The lack of RKIP protein resulted in a pulmonary hypertensive phenotype, exaggerated in hypoxia. Hypoxia induced phosphorylation of RKIP signalling elements in WT pulmonary arteries. RKIP inhibition potentiated mitogen-induced proliferation in lung fibroblasts. These results provide evidence for the involvement of RKIP in suppressing the development of hypoxia-induced PAH in mice.