Vanja Karamatic Crew

Epigenetic Silencing of the Chaperone Cosmc in Human Leukocytes Expressing Tn Antigen

Background: Tn4 B cells from a patient with Tn antigen-positive leukocytes lack transcripts of Cosmc. Results: The Cosmc promoter in Tn4 cells is methylated and 5-aza-2′-deoxycytidine treatment restores Cosmc transcription and normal O-glycans. Conclusion: Methylation-dependent epigenetic silencing of Cosmc occurs in Tn4 cells and results in Tn antigen expression. Significance: These findings provide a novel mechanism underlying aberrant expression of Tn antigen in human diseases. Cosmc is the specific molecular chaperone in the endoplasmic reticulum for T-synthase, a Golgi β3-galactosyltransferase that generates the core 1 O-glycan, Galβ1–3GalNAcα-Ser/Thr, in glycoproteins. Dysfunctional Cosmc results in the formation of inactive T-synthase and consequent expression of the Tn antigen (GalNAcα1-Ser/Thr), which is associated with several human diseases. However, the molecular regulation of expression of Cosmc, which is encoded by a single gene on Xq24, is poorly understood. Here we show that epigenetic silencing of Cosmc through hypermethylation of its promoter leads to loss of Cosmc transcripts in Tn4 cells, an immortalized B cell line from a male patient with a Tn-syndrome-like phenotype. These cells lack T-synthase activity and express the Tn antigen. Treatment of cells with 5-aza-2′-deoxycytidine causes restoration of Cosmc transcripts, restores T-synthase activity, and reduces Tn antigen expression. Bisulfite sequencing shows that CG dinucleotides in the Cosmc core promoter are hypermethylated. Interestingly, several other X-linked genes associated with glycosylation are not silenced in Tn4 cells, and we observed no correlation of a particular DNA methyltransferase to aberrant methylation of Cosmc in these cells. Thus, hypermethylation of the Cosmc promoter in Tn4 cells is relatively specific. Epigenetic silencing of Cosmc provides another mechanism underlying the abnormal expression of the Tn antigen, which may be important in understanding aberrant Tn antigen expression in human diseases, including IgA nephropathy and cancer.

A KEL gene encoding serine at position 193 of the Kell glycoprotein results in expression of KEL1 antigen

BACKGROUND: The KEL2/KEL1 (k/K) blood group polymorphism represents 578C>T in the KEL gene and Thr193Met in the Kell glycoprotein. Anti‐KEL1 can cause severe hemolytic disease of the fetus and newborn. Molecular genotyping for KEL*1 is routinely used for assessing whether a fetus is at risk. Red blood cells (RBCs) from a KEL:1 blood donor (D1) were found to have abnormal KEL1 expression during evaluation of anti‐KEL1 reagents.

Different inactivating mutations in the LU genes of three individuals with the Lutheran-null phenotype

BACKGROUND: The null phenotype of the Lutheran blood group system, Lunull or Lu(a–b–), is characterized by the lack of all Lutheran system antigens. It can arise from three genetic backgrounds: recessive, dominant, or X‐linked. Lunull of the recessive type appears to result from homozygosity for an inactive LU gene.

Two MER2‐negative individuals with the same novel CD151 mutation and evidence for clinical significance of anti‐MER2

BACKGROUND: MER2 (RAPH1), the only antigen of the RAPH blood group system, is located on the tetraspanin CD151. Only four examples of alloanti‐MER2 are known. We report here two new examples of alloanti‐MER2, in women of Pakistani and Turkish origin, one of whom showed signs of a hemolytic transfusion reaction (HTR) after transfusion of 3 units of red cells (RBCs).

Acquired and transient RBC CD55 deficiency (Inab phenotype) and anti-IFC

BACKGROUND: Antigens of the Cromer blood group system reside on the glycoprotein CD55 (decay‐accelerating factor). The Inab phenotype is the null phenotype of this system. So far, only five propositi have been described who exhibit this phenotype, and single‐nucleotide substitutions in the CD55 gene have been found in three of them. This report describes the first example of a patient with an acquired and transient form of the Inab phenotype.

Molecular bases of the antigens of the Lutheran blood group system

BACKGROUND: Lutheran is a complex blood group system consisting of 18 identified antigens. There are four pairs of allelic antigens, whereas others are independently expressed antigens of a high frequency. Lutheran antigens are carried by the Lutheran glycoproteins, which are a product of a single gene LU.