HRF20/CD59 complement regulatory protein expression is phenotype-dependent and inducible by the hypomethylating agent 5-azacytidine on Burkitt's lymphoma cell lines

Mechanisms by which the surface expression of the glycosyl-phosphatidylinositol-anchored complement regulatory proteins decay-accelerating factor (CD55) and CD59 is lost in human leukaemia cell lines

We have investigated the mechanisms of defects in the glycosyl-phosphatidylinositol (GPI)-anchored complement regulatory proteins delay-accelerating factor (DAF) and/or CD59 in a panel of human leukaemia cell lines that lack surface expression of these proteins: U937 (DAF+/CD59-), CEM (DAF-/CD59+), TALL (DAF-/CD59-) and a substrain of Ramos [Ramos(-)] (DAF-/CD59-). Northern blotting and reverse transcription-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 in Ramos(-) in which sufficient mRNA for DAF and CD59 was produced. U937, CEM and TALL cells were not defective in GPI anchor formation as assessed 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/or CD59 in these leukaemia cell lines except for Ramos(-) is virtually undetectable steady-state levels of the relevant mRNA, most likely attributable to lack of transcription in these cell lines. On the other hand, Ramos(-) cells failed to generate a GPI anchor, whereas they normally expressed DAF and CD59 transcripts. The transfection of phosphatidylinositol-glycan class A (PIG-A) cDNA into Ramos(-) cells restored DAF and CD59 expression, indicating that the defective mechanism in GPI anchor formation is similar to that in paroxysmal noctural haemoglobinuria (PNH) cells, i.e. a deficiency of the PIG-A gene product. Thus the mechanisms of the defects of DAF and/or CD59 in human leukaemia cell lines are not uniform, and in most cases are different from that proposed to cause PNH.

The influence of tumour necrosis factor-alpha, interleukin-1 beta and interferon-gamma on the expression and function of the complement regulatory protein CD59 on the human colonic adenocarcinoma cell line HT29

CD59 is a 18-25 kDa glycoprotein which, by inhibiting the formation of the membrane attack complex, protects homologous cells from complement mediated damage. We have described recently the expression and complement regulatory function of CD59 on colonic adenocarcinoma cells both in vivo and in vitro. In this study we have examined the influence of cytokines on the expression and complement regulatory function of CD59 on the colonic adenocarcinoma cell line HT29. CD59 expression on the HT29 cells was up-regulated after stimulation by mononuclear cells activated by mixed lymphocyte reaction and by culture supernatants from activated mononuclear cells. Similarly, a dose-dependent increase in CD59 expression was observed after stimulation with both tumour necrosis factor-alpha and interleukin-1 beta. A dose-dependent increase in the level of CD59 expression was also seen using low concentrations of interferon-gamma (IFN-gamma), while CD59 expression on cells cultured with high IFN-gamma concentrations was comparable to non-stimulated cells. Cytokine treated cells were more resistant to lysis by homologous complement than non-stimulated cells, and the increase in CD59 expression was shown to be partially responsible for this. The present data strengthen the role of CD59 as a possible participant in tumour escape.