A blood group-related polymorphism of CD44 abolishes a hyaluronan-binding consensus sequence without preventing hyaluronan binding.
CD44 is a widely expressed integral membrane protein that acts as a receptor for hyaluronan (HA) and is proposed to be important to cell-extracellular matrix interaction. The Indian (In) blood group antigens reside on CD44, and most individuals express the Inb antigen. Homozygosity for the Ina allele occurs as a rare event and is associated with production of alloantibody to the common Inb antigen after transfusion or pregnancy. The present study demonstrates that a single point mutation (G252 --> C) causes an Arg46 --> Pro substitution, which is responsible for the Inb/Ina polymorphism. Additional mutations were found in In(a+b-) cDNA but were not necessary to the antigenic phenotype as determined in site-directed mutagenesis studies. In studies using CD44 chimeric constructs, Arg46 has previously been shown to be crucial for maintenance of HA-binding ability to a CD44 peptide. However, the present study demonstrates that the Arg46 --> Pro substitution does not reduce HA binding to the intact CD44 protein, which contains two proposed extracellular HA-binding motifs. Down-regulation of HA binding to In(a+b-) CD44 by anti-CD44 monoclonal antibody (mAb) ligands, however, was weakened, although all mAbs tested bound In(a+b-) and In(a-b+) CD44 equally well. Competitive inhibition studies using human anti-Inb also showed that some mAbs that inhibit HA binding to CD44 may do so by interacting with a domain separate from, but affecting the structure of, the Inb epitope.
Telen
M J
MJ
Department of Medicine, Duke University Medical Center, Durham, North Carolina 27710, USA.
Udani
M
M
Washington
M K
MK
Levesque
M C
MC
Lloyd
E
E
Rao
N
N
D000595:Amino Acid Sequence; D000911:Antibodies, Monoclonal / Q000276:immunology; D000937:Antigen-Antibody Reactions; D001483:Base Sequence; D001789:Blood Group Antigens / Q000276:immunology*; D002461:Cell Line, Transformed; D016384:Consensus Sequence; D018076:DNA, Complementary; D006801:Humans; D018960:Hyaluronan Receptors / Q000235:genetics* / Q000276:immunology / Q000378:metabolism; D006820:Hyaluronic Acid / Q000378:metabolism*; D008969:Molecular Sequence Data; D011110:Polymorphism, Genetic; D011485:Protein Binding; D014162:Transfection
D000911:Antibodies, Monoclonal; D001789:Blood Group Antigens; D018076:DNA, Complementary; D018960:Hyaluronan Receptors; D006820:Hyaluronic Acid