No abstract

AQP3 is a water and glycerol channel present on human erythrocytes and in various tissues. By protein and molecular biology analysis, two unrelated probands who developed alloantibodies to the high frequency antigen GIL were found to be AQP3-deficient. The defect is caused by homozygous mutation affecting the 5 donor splice site of intron 5 of the AQP3 gene. This mutation causes the skipping of exon 5 and generates a frameshift and premature stop codon. Functional studies by 90°l ight scattering using a stopped-flow spectrometer revealed the absence of facilitated glycerol transport across red cell membranes from the probands, but the water and urea transports were normal. Expression studies into COS-7 cells followed by flow cytometry analysis showed that only cells transfected with AQP3 cDNA strongly reacted with anti-GIL antibodies. These findings represent the first reported cases of AQP3 deficiency in humans and provide the molecular basis of a new blood group system, GIL, encoded by the AQP3 protein.Integral membrane proteins that facilitate the transport of water or/and solutes belong to the major intrinsic protein (MIP) 1 family and are involved in many physiological processes and the pathophysiology of several clinical disorders (1-4). They are divided into three subgroups according to their sequences and function properties: (i) the aquaporins (AQP), permeable only to water; (ii) the glycerol facilitators, permeable only to glycerol (not present in mammals); and (iii) the aquaglyceroporins, which present a mixed selectivity. AQP1, the archetype of the MIP family selectively permeable to water (5), is present in various tissues including red blood cell (RBC) membranes from which it was first purified (6).The high glycerol permeability of human RBCs is due to aquaglyceroporin AQP3 (7,8), which is moderately permeable to water, highly permeable to glycerol, and to a lesser extent permeable to urea (9 -11). AQP3 is present in rat RBCs but absent from mouse RBCs (8). It is encoded by a single-copy gene composed of six exons distributed over 6 kilobases of DNA located on human chromosome 9p13 (12). The predicted protein of 292 residues is organized into six bilayer-spanning domains with the NH 2 -and COOH termini located intracellularly (13). On human RBCs, AQP3 presumably is glycosylated on all subunits at Asn-141, the putative N-glycosylation site located in loop "c" at the external face of the cell membrane (14).So far, AQP1 and AQP3 are the only two known proteins of the aquaporin family identified in human RBCs. As AQP1 express Colton blood group antigens (15, 16), the question was raised as to whether AQP3 might also be encoded by a blood group gene. We reasoned that if AQP3 carries a blood group specificity, the corresponding antigen should be of high frequency because AQP3 is a common protein of human RBCs. Accordingly, we performed an immunostaining analysis of human RBCs proteins from patients who had developed alloantibodies against high frequency antigens that caused delayed or severe hemolytic ...

No abstract

The Duffy (FY) blood group antigens are carried by the DARC glycoprotein, a widely expressed chemokine receptor. The molecular basis of the Fya/Fyb and Fy(a-b-) polymorphisms has been clarified, but little is known about the Fyxantigen and the FY*X allele associated with weak expression of Fyb, Fy3, Fy5, and Fy6 antigens. We analyzed here the structure and expression of the FY gene in 4 Fy(a-bweak) individuals. As compared with Fy(a-b+) controls, the Fy(a-bweak) red blood cell membranes contained residual amount of DARC polypeptide and these cells were poorly bound by anti-Fy antibodies and chemokines. The FY gene from Fy(a-b+) and Fy(a-bweak) individuals differed by one substitution, C286T. The resulting Arg89Cys amino acid change reduced the binding of anti-Fy antibodies and chemokines to DARC transfectants. We concluded that the Fybweak donors carried theFY*X allele at the FY locus and that the Fyxantigen corresponds to highly reduced expression of a grossly normal Fyb polypeptide caused by the Arg89Cys substitution. Because FY is a single copy gene, this defect should also affect DARC expression in nonerythroid cells. Because the Fyx phenotype is not associated with apparent clinical consequences, we discussed these findings in the light of the putative roles of DARC in various tissues. Finally, we developed a Fyx DNA typing assay that should be useful for genetic studies and clinical transfusion medicine. © 1998 by The American Society of Hematology.