The human peptidylarginine deiminases type 2 and type 4 have distinct substrate specificities.

Human peptidylarginine deiminases (hPADs) have been implicated in several diseases, particularly in rheumatoid arthritis. Since hPAD2 and hPAD4 are the isotypes expressed in the inflamed joints of RA patients and protein citrullination by PADs has been proposed to play a pathophysiological role, they represent unique therapeutic targets. To facilitate the development of substrate-based PAD inhibitors the substrate specificity of hPAD2 and hPAD4 was determined. Recombinant hPADs were expressed in bacteria or mammalian cell lines and allowed to citrullinate proteins in cell lysates, as well as a series of synthetic peptides. The citrullinated residues in proteins and the efficiency of peptide citrullination were determined by mass spectrometry. In total 320 hPAD2 and 178 hPAD4 citrullination sites were characterized. Amino acid residues most commonly found in citrullination sites for both isotypes are Gly at +1 and Tyr at +3 relative to the target arginine. For hPAD4 several additional amino acids were observed to be preferred at various positions from -4 to +4. The substrate motifs determined by amino acid substitution analysis partially confirmed these preferences, although peptide context dependent differences were also observed. Taken together, our data show that the enzyme specificity for cellular substrates and synthetic peptides differs for hPAD2 and hPAD4. hPAD4 shows more restrictive substrate specificity compared to hPAD2. Consensus sequences, which can be used as the basis for the development of PAD inhibitors, were derived for the citrullination sites of both hPAD2 and hPAD4.

A CD40-CD95L fusion protein interferes with CD40L-induced prosurvival signaling and allows membrane CD40L-restricted activation of CD95.

We analyzed a novel bifunctional fusion protein, CD40ed-CD95Led, consisting amino-terminally of the extracellular domain of CD40 and carboxy-terminally of the extracellular domain of CD95L. On cells lacking CD40L, this fusion protein is poorly active with respect to CD95 activation [median effective dose (ED50)>1 microg/ml], but it stimulates CD95 signaling with high efficiency upon binding to membrane-expressed CD40L (ED50<1 ng/ml). Thus, cell surface immobilization mediated by the CD40 part of the molecule unmasks the high-latent, CD95-stimulating capacity of the otherwise poorly active CD95L fusion protein. Moreover, interaction of the CD40 part of CD40ed-CD95Led with CD40L prevents the activation of cellular CD40. The CD40ed-CD95Led fusion protein therefore simultaneously blocks antiapoptotic CD40 activation and induces CD95-mediated apoptosis. Indeed, T47D cells displaying an antiapoptotic autocrine CD40-CD40L signaling loop were significantly more sensitive toward CD40ed-CD95Led than toward soluble CD95L artificially activated by crosslinking. Fusion proteins of RANK and CD95L (RANKed-CD95Led) and CD40 and tumor necrosis factor-related apoptosis inducing ligand (TRAIL) (CD40ed-TRAILed), with domain architectures similar to CD40ed-Cd95Led, displayed RANKL-dependent CD95 and CD40L-dependent TRAILR2 activation, respectively, indicating the principle feasibility of this fusion protein design.

A three base pair gene variation within the distal 5'-flanking region of the interleukin-10 (IL-10) gene is related to the in vitro IL-10 production capacity of lipopolysaccharide-stimulated peripheral blood mononuclear cells.

Interleukin-10 (IL-10) is an important multifunctional immunmodulator. There is evidence that IL-10 secretion is associated with certain genetic elements of the proximal IL-10 gene 5'-flanking region. The allelic and genotypic comparison of IL-10 expression by lipopolysaccharide (LPS)- stimulated leukocytes (PBMC) with a recently discovered distal "indel" DNA-sequence variation at - 7400 bp revealed significant inter-individual differences in the IL-10 in vitro production capacity. Homozygotes lacking the three base pairs "GGA" (- 7400del) at this gene locus are characterised by high expression of IL-10 with a median of 1690pg/ml (P

Generation of a FasL-based proapoptotic fusion protein devoid of systemic toxicity due to cell-surface antigen-restricted Activation.

We describe the construction of a FasL fusion protein devoid of systemic toxicity, inducing apoptosis only on cell-surface antigen-positive cells. The fusion protein consists carboxyl-terminally of the extracellular domain of FasL and amino-terminally of a fibroblast activation protein (FAP)-specific single chain antibody fragment (sc40-FasL). The latter allows immobilization-dependent conversion of the inactive soluble FasL fusion protein into an entity with membrane FasL-like activity. Thus, sc40-FasL efficiently induced apoptosis only in FAP-expressing cells. In accordance with a strict target-selective activity of sc40-FasL, the intravenous application of this reagent in mice revealed no signs of systemic toxicity and prevented growth of xenotransplanted FAP-positive (but not FAP-negative) tumor cells. The principle described here for the first time, in which cell-surface antigen-mediated activation of Fas permits local activation of Fas in vivo, opens novel avenues for the use of Fas signaling in cancer therapy.