title: Regulation of ALK-1 signaling by the nuclear receptor LXRbeta.
abstract: The transforming growth factor beta (TGF-beta) receptor, ALK-1, is expressed specifically on endothelial cells and is essential for angiogenesis, as demonstrated by its targeted deletion in mice and its mutation in the human disease hereditary hemorrhagic telangiectasia. Although ALK-1 and another endothelial-specific TGF-beta receptor, endoglin, both bind TGF-beta with identical isoform specificity and form a complex together, neither has been shown to signal in response to TGF-beta, and the mechanism by which these receptors signal in endothelial cells remains unknown. Here we report the identification of the nuclear receptor liver X receptor beta (LXRbeta) as a modulator/mediator of ALK-1 signaling. The cytoplasmic domain of ALK-1 specifically binds to LXRbeta in vitro and in vivo. Expression of activated ALK-1 results in translocation of LXRbeta from the nuclear compartment to the cytoplasmic compartment. The interaction of activated ALK-1 with LXRbeta in the cytoplasmic compartment results in the specific phosphorylation of LXRbeta by ALK-1, primarily on serine residues. LXRbeta subsequently modulates signaling by ALK-1 and the closely related TGF-beta receptor, ALK-2, as demonstrated by specific and potent inhibition of ALK-1- and ALK-2-mediated transcriptional responses, establishing LXRbeta as a potential modulator/mediator of ALK-1/ALK-2 signaling.
authors.affiliation: Department of Medicine, Howard Hughes Medical Institute, Duke University Medical Center, Durham, North Carolina 27710, USA.
authors.forename: Jinyao
authors.initials: J
authors.lastname: Mo
authors.forename: Shijing J
authors.initials: SJ
authors.lastname: Fang
authors.forename: Wei
authors.initials: W
authors.lastname: Chen
authors.forename: Gerard C
authors.initials: GC
authors.lastname: Blobe
mesh_terms: D030201:Activin Receptors, Type I / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D030301:Activin Receptors, Type II; D000595:Amino Acid Sequence; D000596:Amino Acids / Q000032:analysis; D000818:Animals; D001665:Binding Sites; D019556:COS Cells; D002460:Cell Line; D002522:Chlorocebus aethiops; D004268:DNA-Binding Proteins; D005260:Female; D015723:Gene Library; D006801:Humans; D000071518:Liver X Receptors; D008168:Lung / Q000502:physiology; D008297:Male; D008969:Molecular Sequence Data; D009928:Organ Specificity; D057093:Orphan Nuclear Receptors; D010766:Phosphorylation; D021381:Protein Transport; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D011994:Recombinant Proteins / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics; D015398:Signal Transduction; D014162:Transfection
chemical_list: D000596:Amino Acids; D004268:DNA-Binding Proteins; D000071518:Liver X Receptors; D057093:Orphan Nuclear Receptors; D018160:Receptors, Cytoplasmic and Nuclear; D011994:Recombinant Proteins; C425364:ACVRL1 protein, human; D030201:Activin Receptors, Type I; D030301:Activin Receptors, Type II