ADP-Ribosylation Regulates the Signaling Function of IFN-γ

Murine T cells express the GPI-anchored ADP-ribosyltransferase 2.2 (ARTC2.2) on the cell surface. In response to T cell activation or extracellular NAD(+) or ATP-mediated gating of the P2X7 ion channel ARTC2.2 is shed from the cell surface as a soluble enzyme. Shedding alters the target specificity of ARTC2.2 from cell surface proteins to secreted proteins. Here we demonstrate that shed ARTC2.2 potently ADP-ribosylates IFN-gamma in addition to other cytokines. Using mass spectrometry, we identify arginine 128 as the target site of ADP-ribosylation. This residue has been implicated to play a key role in binding of IFN-gamma to the interferon receptor 1 (IFNR1). Indeed, binding of IFN-gamma to IFNR1 blocks ADP-ribosylation of IFN-gamma. Moreover, ADP-ribosylation of IFN-gamma inhibits the capacity of IFN-gamma to induce STAT1 phosphorylation in macrophages and upregulation of the proteasomal subunit ss5i and the proteasomal activator PA28-alpha in podocytes. Our results show that ADP-ribosylation inhibits the signaling functions of IFN-gamma and point to a new regulatory mechanism for controlling signaling by IFN-gamma.

Automated summary

The shedding of ARTC2.2 from murine T cells leads to potent ADP-ribosylation of IFN-gamma, affecting its binding to the interferon receptor and subsequently inhibiting its signaling functions. This study highlights a new regulatory mechanism for controlling signaling by IFN-gamma through ADP-ribosylation.