Characterization of the histo-blood group O(2) gene and its protein product.
OBJECTIVE
This study aimed to show the full sequence and function of the O(2) allele, and investigate whether it accounts for the incompatible expression of A antigens in gastric carcinomas of blood group O persons.


METHODS
By PCR, we determined the ABO genotype of group O subjects (76 gastric carcinoma patients and 165 blood donors). Two expression constructs, encoding either the putative soluble or full-length O(2) protein, were used to transfect Sf9 cells. The expression and the activity of the O(2) protein were analysed by immunohistochemistry and enzymatic assays, respectively.


RESULTS
No significant difference was detectable between the O(2) allele frequency in gastric carcinoma patients (3.9%) and blood donors (4.2%). Sequencing analysis of the O(2) allele revealed an intact reading frame identical to that of A transferase except for four nucleotide substitutions. O(2)-transfected Sf9 cells and gastric carcinomas genotyped as O(1)O(2) both expressed a protein recognized by anti-A/B transferase monoclonal antibodies. In enzymatic assays, the O(2) protein failed to show measurable A transferase activity.


CONCLUSIONS
The O(2) allele has an intact reading frame encoding a protein immunologically related to A/B transferases and enzymatically inactive. Further, our data gave no indication that the O(2) allele is related to the phenomenon of incompatible A antigen expression in gastric cancer.
Amado
M
M
Institute of Molecular Pathology and Immunology of University of Porto, IPATIMUP, Porto, Portugal.
Bennett
E P
EP
Carneiro
F
F
Clausen
H
H
D000017:ABO Blood-Group System / Q000235:genetics* / Q000378:metabolism; D000483:Alleles; D000911:Antibodies, Monoclonal; D001782:Blood Donors; D005753:Gastric Mucosa / Q000201:enzymology / Q000378:metabolism; D005787:Gene Frequency; D006801:Humans; D007150:Immunohistochemistry; D016366:Open Reading Frames; D017354:Point Mutation; D012334:RNA, Neoplasm / Q000032:analysis; D017423:Sequence Analysis, RNA; D013274:Stomach Neoplasms / Q000097:blood / Q000201:enzymology / Q000473:pathology; D014166:Transferases / Q000235:genetics / Q000276:immunology / Q000378:metabolism
D000017:ABO Blood-Group System; D000911:Antibodies, Monoclonal; D012334:RNA, Neoplasm; D014166:Transferases