Metalloprotease-mediated shedding of enzymatically active mouse ecto-ADP-ribosyltransferase ART2.2 upon T cell activation

T cells proteolytically shed the ectodomains of several cell surface protei ns and, thereby, can alter their responsiveness and can release soluble int ercellular regulators. ART2.2 is a GPI-anchored ecto-ADP-ribosyltransferase (ART) related to ADP-ribosylating bacterial toxins. ART2.2 is expressed ex clusively by mature T cells. Here we show that ART2.2 is shed from the cell surface in enzymatically active form upon activation of T cells. Shedding of ART2.2 resembles that of L-selectin (CD62L) in dose response, kinetics o f release, and sensitivity to the metalloprotease inhibitor Immunex Compoun d 3, suggesting that ART2.2, like CD62L, is cleaved by TNF-alpha-converting enzyme or by another metalloprotease. ART2.2 shed from activated T cells m igrates slightly faster in SDS-PAGE analyses than does ART2.2 released upon cleavage of the GPI anchor. This indicates that shedding of ART2.2 is medi ated by proteolytic cleavage close to its membrane anchor. Shed ART2.2 is e nzymatically active and ADP-ribosylates several substrates in vitro. Thus, shedding of ART2.2 releases a potential intercellular regulator. Finally, u sing a new FAGS assay for monitoring ADP-ribosylation of cell surface prote ins, we demonstrate that shedding of ART2.2 correlates with a reduced sensi tivity of T cell surface proteins to ADP-ribosylation. Our findings suggest that by shedding ART2.2 the activated T cell not only releases a potential intercellular regulator but also may alter its responsiveness to immune re gulation by ART2.2-mediated ADP-ribosylation of cell surface proteins.