MOLECULAR CHARACTERIZATION OF A GLYCOSYLPHOSPHATIDYLINOSITOL-LINKED ADP-RIBOSYLTRANSFERASE FROM LYMPHOCYTES

Mono-ADP-ribosyltransferases catalyze the transfer of the ADP-ribose m oiety of nicotinamide adenine dinucleotide (NAD) to proteins. It was r eported by Wang et al (J Immunol 153:4048, 1994) that incubation of mo use cytotoxic T lymphocytes (CTL) with NAD resulted in the ADP-ribosyl ation of membrane proteins and inhibition of cell proliferation and cy totoxicity. Treatment of CTL with phosphatidylinositol-specific phosph olipase C (PI-PLC) before incubation with NAD prevented the inhibitory effects of NAD on the cells, consistent with the removal of a glycosy lphosphatidylinositol (GPI)-anchored ADP-ribosyltransferase on the lym phocyte surface. We have identified and cloned a GPI-linked ADP-ribosy ltransferase from Yac-l mouse T-cell lymphoma cells. The deduced amino acid sequence of the Yac-l transferase was 70% and 41% identical to t hose of the rabbit skeletal muscle and chicken heterophil, respectivel y, it contained three noncontiguous sequences similar to those found i n several of the bacterial toxin and vertebrate ADP-ribosyltransferase s. Based on crystallography of the bacterial toxins, these regions are believed to form, in part, the catalytic site consistent with a commo n mechanism for the ADP-ribose transfer reaction, In rat mammary adeno carcinoma (NMU) cells transformed with the Yac-l transferase cDNA, tra nsferase activity was present on the cell surface and was released int o the medium by treatment of cells with PI-PLC, Thus, we have cloned a novel gene that has properties identical to the transferase detected in CTL, and may be involved in the NAD-dependent regulation of prolife ration and cytotoxicity.