| Research Abstract |
We investigated the mechanisms of defects of glycosyl-phosphatidylinositol (GPI) -anchored complement regulatory proteins, DAF and/or CD59, in a panel of human leukemia cell lines that lack surface expression of these proteins : U937 (DAF^+/CD59^-), CEM (DAF^<-E1S1+>), TALL (DAF^-/CD59^-), and a substrains of Ramos [Ramos (-)] (DAF^-/CD59^-), Northe blot and reverse transcriptase-polymerase chain reaction (RT-PCR) revealed that the main cause of the DAF and/or CD59 deficiency is the failure of mRNA expression in most of the cell lines except for Ramos (-) which allowed the generation of the sufficient mRNA of DAF and CD59 U937, CEM,and TALL cells were not defective in GPI anchor formation as assesse by the detection of other GPI-anchored proteins. No gene abnormality corresponding to DAF or CD59 was detected by Southern blotting. Thus, the cause of the defects of DAF and/CD59 in these leukemia cell lines except for Ramos (-) is virtually undetectable steady state levels of the relevant mRNA,most likely, is attributable to aberrance at the transcription steps in these cell lines. On the other hand, Ramos (-) cells failed to generate a GPI anchor, whereas it normally expressed DAF and CD59 transcripts. The transfection of PIGA cDNA to Ramos (-) cells restored the DAF and CD59 expression, indicating that the mechanism defective in GPI-anchor formation is similar to that of paroxysmal nocturnal hemoglobinuria (PNH) cells, a deficiency of the PIG-A gene product. Thus, the mechanisms of the defects of DAF and/or CD59 in human leukemia cell lines are not uniform and are mostly different from that proposed to cause PNH.
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