ABO blood group A transferases catalyze the biosynthesis of FORS blood group FORS1 antigen upon deletion of exon 3 or 4

Abstract

Key Points• ABO blood group A transferases possess intrinsic FS activity upon deletion of exon 3 or 4 of A transferase messenger RNAs.• Cointroduction of exon 3 or 4 deletion and GlyGlyAla substitution synergistically confers human A transferases with strong FS activity. (B3GALNT1) cells, and cell-surface expression of FORS1 was immunologically monitored. To our surprise, the deletion of exon 3 or 4, but not of exon 2 or 5, of human AT transcripts bestowed moderate FS activity, indicating that the A allele is inherently capable of producing a protein with FS activity. Because RNA splicing is frequently altered in cancer, this mechanism may explain, at least partially, the appearance of FORS1 in human cancer. Furthermore, strong FS activity was attained, in addition to AT and BT activities, by cointroducing 1 of those deletions and the GlyGlyAla substitution, possibly by the synergistic effects of altered intraGolgi localization/conformation by the former and modified enzyme specificity by the latter.

Blood group ABO gene–encoded A transferase catalyzes the biosynthesis of FORS1 antigen of FORS system upon Met69Thr/Ser substitution

“…The current study showed that this construct also exhibited weak FS activity and that the Met69Thr substitution was responsible for the FS activity. Together with our previous finding that the GlyGlyAla substitution at codons 266 to 268 of human AT and the deletion of exon 3 or 4 of AT mRNAs also endowed FS activity, 14,16 it is evident that multiple molecular mechanisms exist allowing the crosstalk between ABO and FORS systems. The fact that FS activity was enhanced by the cointroduction of GlyGlyAla tripeptide and Met69Thr substitutions suggests 2 different synergistic mechanisms.…”

“…Human AT and derivatives having GlyGlyAla or MetGlyAla tripeptide, mouse cis-AB transferase, and mouse FS constructs H_ABO-A, H_ABO-A(GlyGlyAla), H_ABO-A(MetGlyAla), M_ABO-AB, and M_GBGT1, respectively, were prepared in the pSG5 eukaryotic expression plasmid vector as previously described. 7,14,16 Additional amino acid substitution constructs were prepared by in vitro mutagenesis, employing the 2-round primermediated polymerase chain reaction strategy using primers with nucleotide substitutions. 7,16 DNA transfection…”

“…7,14,16 Additional amino acid substitution constructs were prepared by in vitro mutagenesis, employing the 2-round primermediated polymerase chain reaction strategy using primers with nucleotide substitutions. 7,16 DNA transfection…”

“…In recent years, we have been interested in another blood group system: Forssman (FORS). [13][14][15][16] The Forssman antigen (FORS1) was initially recognized as an antigen in guinea pig and sheep, but not in rabbit. 17 Using antibodies against this antigen, species were categorized into FORS1 antigen-positive and antigen-negative species.…”

“…Surprisingly, we discovered that the deletion of exons 3 or 4 of human AT cDNA, but not of exons 2 or 5, granted the encoded proteins with moderate FS activity. 16 This crosstalk between ABO and GBGT1 genes may explain, at least partially, why some FORS1-negative individuals express FORS1 in malignant cells/tissues as alterations in messenger RNA (mRNA) splicing are frequent in cancer. [24][25][26] We also observed an enhanced FS activity by cointroducing the GlyGlyAla substitution with the deletion of exons 3 or 4.…”