title: Activin receptor-like kinase 2 and Smad6 regulate epithelial-mesenchymal transformation during cardiac valve formation.
abstract: Epithelial-mesenchymal transformation (EMT) occurs during both development and tumorigenesis. Transforming growth factor beta (TGFbeta) ligands signal EMT in the atrioventricular (AV) cushion of the developing heart, a critical step in valve formation. TGFbeta signals through a complex of type I and type II receptors. Several type I receptors exist although activin receptor-like kinase (ALK) 5 mediates the majority of TGFbeta signaling. Here, we demonstrate that ALK2 is sufficient to induce EMT in the heart. Both ALK2 and ALK5 are expressed throughout the heart with ALK2 expressed abundantly in endocardial cells of the outflow tract (OFT), ventricle, and AV cushion. Misexpression of constitutively active (ca) ALK2 in non-transforming ventricular endocardial cells induced EMT, while caALK5 did not, thus demonstrating that ALK2 activity alone is sufficient to stimulate EMT. Smad6, an inhibitor of Smad signaling downstream of ALK2, but not ALK5, inhibited EMT in AV cushion endocardial cells. These data suggest that ALK2 activation may stimulate EMT in the AV cushion and that Smad6 may act downstream of ALK2 to negatively regulate EMT.
authors.affiliation: Department of Pharmacology, Vanderbilt University Medical Center, Room 476 RRB, 2220 Pierce Avenue, Nashville, TN 37232-6600, USA.
authors.forename: Jay S
authors.initials: JS
authors.lastname: Desgrosellier
authors.forename: Nathan A
authors.initials: NA
authors.lastname: Mundell
authors.forename: Maureen A
authors.initials: MA
authors.lastname: McDonnell
authors.forename: Harold L
authors.initials: HL
authors.lastname: Moses
authors.forename: Joey V
authors.initials: JV
authors.lastname: Barnett
mesh_terms: D030201:Activin Receptors, Type I / Q000235:genetics / Q000378:metabolism; D030301:Activin Receptors, Type II / Q000235:genetics / Q000378:metabolism*; D000256:Adenoviridae / Q000235:genetics / Q000378:metabolism; D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D002642:Chick Embryo; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004699:Endocardium / Q000378:metabolism; D004848:Epithelium / Q000502:physiology*; D018014:Gene Transfer Techniques; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D006351:Heart Valves / Q000166:cytology / Q000196:embryology*; D017403:In Situ Hybridization; D008648:Mesoderm / Q000502:physiology*; D009024:Morphogenesis / Q000502:physiology*; D017346:Protein Serine-Threonine Kinases; D000077293:Receptor, Transforming Growth Factor-beta Type I; D018125:Receptors, Transforming Growth Factor beta / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D051905:Smad6 Protein; D015534:Trans-Activators / Q000378:metabolism*; D016212:Transforming Growth Factor beta / Q000378:metabolism
chemical_list: D004268:DNA-Binding Proteins; D018125:Receptors, Transforming Growth Factor beta; D051905:Smad6 Protein; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; D049452:Green Fluorescent Proteins; D017346:Protein Serine-Threonine Kinases; D030201:Activin Receptors, Type I; D030301:Activin Receptors, Type II; D000077293:Receptor, Transforming Growth Factor-beta Type I; D000469:Alkaline Phosphatase