Abstracts (complete list) - Wissenschaft Online

Sabrina Laing, Mareike Pilz, Michel Seman, Friedrich Koch-Nolte, Friedrich Haag
Human TNF&alpha is a substrate for modification by ADPribosyltransferase-1
(ART1)
Mono-ADP-ribosyltransferases (ARTs) are GPI-anchored ectoenzymes that covalently
modify cell surface or soluble target proteins by transferring ADP-ribose from NAD+ to
arginine residues. In the mouse, ART2, expressed on resting T lymphocytes, plays an
immunoregulatory role by ADP-ribosylating the P2X7 purinoreceptor, thereby initiating
rapid apoptosis in T-cells. ART2 is shed from the cell surface in an enzymatically active
form upon T-cell activation. However, ART2 is a pseudogene in man, and the question
as to whether ADP-ribosylation plays an immunoregulatory role in the human immune
system is open. We asked whether in humans the immunoregulatory function of ART2
might be carried out by ART1. We identified ART1 transcripts in human peripheral blood
leukocytes, as well as in heart and skeletal muscle, by RT-PCR analysis. We
hypothesized that ART1, like ART2, might be released from cells and be present in the
circulation in a soluble form. We thus asked whether soluble ART1 could modify small
messenger proteins such as cytokines. Indeed, soluble ART1, released from the surface
of transfected cells by PI-PLC, modified recombinant human TNF&alpha in vitro.
Furthermore, co-transfection of HEK293 cells with ART1 and human TNF&alpha resulted
in modification of TNF&alpha at at least 2 distinct sites, i.e. one within the domain shed
from the cell surface by the action of the metalloproteinase TNF&alpha Converting
Enzyme (TACE), and one on the stalk that remains connected with the cell membrane
after cleavage by TACE. Experiments to investigate the functional consequences of ADPribosylation
of TNF&alpha as well as to identify the ADP-ribosylation sites are currently
in progress.