Regulation of cytotoxic T cells by ecto-nicotinamide adenine dinucleotide (NAD) correlates with cell surface GPI-anchored/arginine ADP- ribosyltransferase

This report demonstrates that incubation of cytotoxic T cells with NAD causes suppression of their ability to proliferate in response to stimulator cells or to lyse targets. Effects are evident after incubation for 3 h with concentrations of NAD as low as 1 μM and are sustained for many hours after removal of NAD from culture media. Suppression is a result of the failure of CTL to form specific conjugates with targets as well as a lower level of activation in response to TCR-mediated stimulation, although TCR-mediated transmembrane signaling is demonstrable. Metabolites of NAD such as nicotinamide, ADP-ribose, and cyclic-ADP-ribose have no detectable effect, indicating that NAD-glycohydrolase or ADP-ribose cyclase do not mediate suppression. Incubation of intact CTL with [³²P]NAD leads to incorporation of ³²P into a particulate, subcellular fraction, a reaction that is not inhibitable by ADP-ribose. Hydroxylamine, but not mercuric ion releases [³²P]ADP-ribose, whereas phosphodiesterase releases [³²P]AMP from the particulate subcellular fraction, suggesting that labeling is a result of enzymatic mono-ADP-ribosylation of arginines. In support of this, treatment of intact CTL with phosphatidylinositol-specific phospholipase C releases an arginine-specific ADP-ribosyltransferase and causes insensitivity to ecto- NAD suppression. These results suggest that a GPI-anchored ADP- ribosyltransferase uses ecto-NAD to ADP-ribosylate proteins that regulate CTL function.