title: BMP4 induces HO-1 via a Smad-independent, p38MAPK-dependent pathway in pulmonary artery myocytes.
abstract: Bone morphogenetic proteins (BMPs) are multifunctional cytokines, which play a key role in vascular development and remodeling. Heme oxygenase-1 (HO-1), the rate-limiting enzyme in heme catabolism, has been shown to be protective against vascular and lung injury. In a microarray study, we identified HO-1 as a major target of BMP4 signaling in human pulmonary artery smooth muscle cells (PASMCs), and confirmed the induction of HO-1 mRNA and protein by RT-PCR and Western blotting, respectively. Immunoblotting demonstrated that incubation of PASMCs with BMP4 rapidly phosphorylated Smad1/5 and activated the mitogen-activated protein kinases, p38(MAPK) and ERK1/2, in PASMCs, but not JNK. Using pathway selective inhibitors, the induction of HO-1 mRNA and protein was shown to be dependent on activation of p38(MAPK). Induction was independent of Smad1/5 signaling, since HO-1 mRNA and protein induction was intact in PASMCs harboring mutations in the kinase domain of BMP type II receptor, with disrupted Smad signaling. In addition, adenoviral transfection of kinase-deficient BMPR-II also failed to inhibit BMP4-induced HO-1 expression. In functional studies, the HO-1 inhibitor, ZnPP-IX, partly reversed the growth-inhibitory effects of BMP4, and overexpression of HO-1 in PASMCs inhibited serum-stimulated [3H]-thymidine incorporation. Taken together, these findings show that HO-1 is an important Smad-independent target of BMP signaling in vascular smooth muscle. Inhibition of HO-1 function or expression will further increase the proproliferative capacity of BMPR-II-deficient PASMCs and may thus represent a potential "second hit" necessary for disease manifestation.
authors.affiliation: Department of Medicine, University of Cambridge, Addenbrooke's and Papworth Hospitals, Cambridge, United Kingdom.
authors.forename: Xudong
authors.initials: X
authors.lastname: Yang
authors.forename: Patty J
authors.initials: PJ
authors.lastname: Lee
authors.forename: Lu
authors.initials: L
authors.lastname: Long
authors.forename: Richard C
authors.initials: RC
authors.lastname: Trembath
authors.forename: Nicholas W
authors.initials: NW
authors.lastname: Morrell
mesh_terms: D000818:Animals; D055415:Bone Morphogenetic Protein 4; D019485:Bone Morphogenetic Proteins / Q000502:physiology*; D002417:Cattle; D049109:Cell Proliferation; D002478:Cells, Cultured; D004790:Enzyme Induction / Q000502:physiology; D051547:Heme Oxygenase-1 / Q000096:biosynthesis*; D006801:Humans; D032389:Myocytes, Smooth Muscle / Q000201:enzymology*; D011651:Pulmonary Artery / Q000166:cytology*; D011817:Rabbits; D015398:Signal Transduction / Q000502:physiology*; D051785:Smad Proteins / Q000502:physiology*; D048051:p38 Mitogen-Activated Protein Kinases / Q000502:physiology*
chemical_list: C525809:BMP4 protein, human; D055415:Bone Morphogenetic Protein 4; D019485:Bone Morphogenetic Proteins; D051785:Smad Proteins; C496541:HMOX1 protein, human; D051547:Heme Oxygenase-1; D048051:p38 Mitogen-Activated Protein Kinases