Activin receptor-like kinase 2 and Smad6 regulate epithelial-mesenchymal transformation during cardiac valve formation.

Desgrosellier JS, Mundell NA, McDonnell MA, Moses HL, Barnett JV
Dev Biol. 2005 280 (1): 201-10

PMID: 15766759 · DOI:10.1016/j.ydbio.2004.12.037

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.

MeSH Terms (22)

Activin Receptors, Type I Activin Receptors, Type II Adenoviridae Alkaline Phosphatase Animals Chick Embryo DNA-Binding Proteins Endocardium Epithelium Gene Transfer Techniques Green Fluorescent Proteins Heart Valves In Situ Hybridization Mesoderm Morphogenesis Protein-Serine-Threonine Kinases Receptor, Transforming Growth Factor-beta Type I Receptors, Transforming Growth Factor beta Signal Transduction Smad6 Protein Trans-Activators Transforming Growth Factor beta

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