Analysis of ALK-1 and endoglin in newborns from families with hereditary hemorrhagic telangiectasia type 2.
ALK-1 (activin receptor-like kinase-1), a type I receptor of the transforming growth factor (TGF)-beta superfamily, is the gene mutated in hereditary hemorrhagic telangiectasia type 2 (HHT2) while endoglin is mutated in HHT1. Using a novel polyclonal antibody to ALK-1, we measured ALK-1 expression on human umbilical vein endothelial cells (HUVEC) of newborns from HHT families whose affected members had normal endoglin levels. ALK-1 levels were specifically reduced in three HUVEC with ALK-1 missense mutant codons, and normal in two newborns not carrying the missense mutations present in the clinically affected relatives. Levels were also normal in a HUVEC with deletion of S232 in the ATP binding site of ALK-1. Thus HHT2 appears to be associated with a loss of function of the mutant allele due to a reduction in either protein level or activity. We also report three new ALK-1 missense mutations leading to G48E/A49P, C344Y and E407D substitutions. In COS-1 transfected cells, ALK-1 was found in the TGF-beta1 and -beta3 receptor complexes in association with endoglin and TbetaRII, but not in activin receptor complexes containing endoglin. In HUVEC, ALK-1 was not detectable in the TGF-beta1 or -beta3 receptor complexes. However, in the absence of ligand, ALK-1 and endoglin interactions were observed by immunoprecipitation/western blot in HUVEC from normal as well as HHT1 and HHT2 patients. Our data suggest a transient association between these two proteins of the TGF-beta superfamily, both required at a critical level to ensure vessel wall integrity.
Abdalla
S A
SA
Cancer and Blood Research Programme, The Hospital for Sick Children, and Department of Immunology, University of Toronto, Toronto M5G 1X8, Canada.
Pece-Barbara
N
N
Vera
S
S
Tapia
E
E
Paez
E
E
Bernabeu
C
C
Letarte
M
M
D029404:Activin Receptors; D019943:Amino Acid Substitution; D015703:Antigens, CD; D001483:Base Sequence; D002478:Cells, Cultured; D000071063:Endoglin; D004730:Endothelium, Vascular / Q000502:physiology; D005190:Family; D005260:Female; D018392:Genomic Imprinting; D006801:Humans; D007231:Infant, Newborn; D020125:Mutation, Missense; D010920:Placenta / Q000502:physiology; D011247:Pregnancy; D017346:Protein Serine-Threonine Kinases / Q000235:genetics*; D011956:Receptors, Cell Surface; D018125:Receptors, Transforming Growth Factor beta / Q000235:genetics; D017384:Sequence Deletion; D013683:Telangiectasia, Hereditary Hemorrhagic / Q000235:genetics*; D014471:Umbilical Veins; D019010:Vascular Cell Adhesion Molecule-1 / Q000235:genetics*
D015703:Antigens, CD; C064206:ENG protein, human; D000071063:Endoglin; D011956:Receptors, Cell Surface; D018125:Receptors, Transforming Growth Factor beta; D019010:Vascular Cell Adhesion Molecule-1; D017346:Protein Serine-Threonine Kinases; D029404:Activin Receptors