Augustin Amour

TNF‐α converting enzyme (TACE) is inhibited by TIMP‐3

TNF‐α converting enzyme (TACE; ADAM‐17) is a membrane‐bound disintegrin metalloproteinase that processes the membrane‐associated cytokine proTNF‐α to a soluble form. Because of its putative involvement in inflammatory diseases, TACE represents a significant target for the design of specific synthetic inhibitors as therapeutic agents. In order to study its inhibition by tissue inhibitors of metalloproteinases (TIMPs) and synthetic inhibitors of metalloproteinases, the catalytic domain of mouse TACE (rTACE) was overexpressed as a soluble Ig fusion protein from NS0 cells. rTACE was found to be well inhibited by peptide hydroxamate inhibitors as well as by TIMP‐3 but not by TIMP‐1, ‐2 and ‐4. These results suggest that TIMP‐3, unlike the other TIMPs, may be important in the modulation of pathological events in which TNF‐α secretion is involved.

The in vitro activity of ADAM-10 is inhibited by TIMP-1 and TIMP-3

A recombinant soluble form of the catalytic domain of human ADAM‐10 was expressed as an Fc fusion protein from myeloma cells. The ADAM‐10 was catalytically active, cleaving myelin basic protein and peptides based on the previously described ‘metallosheddase’ cleavage sites of tumour necrosis factor α, CD40 ligand and amyloid precursor protein. The myelin basic protein degradation assay was used to demonstrate that hydroxamate inhibitors of matrix metalloproteinases (MMPs) were also inhibitors of ADAM‐10. The natural MMP inhibitors, TIMP‐2 and TIMP‐4 were unable to inhibit ADAM‐10, but TIMP‐1 and TIMP‐3 were inhibitory. Using a quenched fluorescent substrate assay and ADAM‐10 we obtained approximate apparent inhibition constants of 0.1 nM (TIMP‐1) and 0.9 nM (TIMP‐3). The TIMP‐1 inhibition of ADAM‐10 could therefore prove useful in distinguishing its activity from that of TACE, which is only inhibited by TIMP‐3, in cell based assays.

Heparan sulfate regulates amyloid precursor protein processing by BACE1, the Alzheimer's β-secretase

Cleavage of amyloid precursor protein (APP) by the Alzheimers β-secretase (BACE1) is a key step in generating amyloid β-peptide, the main component of amyloid plaques. Here we report evidence that heparan sulfate (HS) interacts with β-site APP-cleaving enzyme (BACE) 1 and regulates its cleavage of APP. We show that HS and heparin interact directly with BACE1 and inhibit in vitro processing of peptide and APP substrates. Inhibitory activity is dependent on saccharide size and specific structural characteristics, and the mechanism of action involves blocking access of substrate to the active site. In cellular assays, HS specifically inhibits BACE1 cleavage of APP but not alternative cleavage by α-secretase. Endogenous HS immunoprecipitates with BACE1 and colocalizes with BACE1 in the Golgi complex and at the cell surface, two of its putative sites of action. Furthermore, inhibition of cellular HS synthesis results in enhanced BACE1 activity. Our findings identify HS as a natural regulator of BACE1 and suggest a novel mechanism for control of APP processing.

The enzymatic activity of ADAM8 and ADAM9 is not regulated by TIMPs

The ADAM family of proteases are type I transmembrane proteins with both metalloproteinase and disintegrin containing extracellular domains. ADAMs are implicated in the proteolytic processing of membrane‐bound precursors and involved in modulating cell–cell and cell–matrix interactions. ADAM8 (MS2, CD156) has been identified in myeloid and B cells. In this report we demonstrate that soluble ADAM8 is an active metalloprotease in vitro and is able to hydrolyse myelin basic protein and a variety of peptide substrates based on the cleavage sites of membrane‐bound cytokines, growth factors and receptors which are known to be processed by metalloproteinases. Interestingly, although ADAM8 was inhibited by a number of peptide analogue hydroxamate inhibitors, it was not inhibited by the tissue inhibitors of metalloproteinases (TIMPs). We also demonstrate that the activity of recombinant soluble ADAM9 (meltrin‐γ, MDC9) lacks inhibition by the TIMPs, but can be inhibited by hydroxamate inhibitors. The lack of TIMP inhibition of ADAM8 and 9 contrasts with other membrane‐associated metalloproteinases characterised to date in this respect (ADAM10, 12, 17, and the membrane‐type metalloproteinases) which have been implicated in protein processing at the cell surface.

Localization of the Death Domain of Tissue Inhibitor of Metalloproteinase-3 to the N Terminus METALLOPROTEINASE INHIBITION IS ASSOCIATED WITH PROAPOPTOTIC ACTIVITY

The tissue inhibitors of metalloproteinases (TIMPs) are a family of four secreted inhibitors of matrix metalloproteinases (MMPs). Recently, additional functions have been attributed to the TIMPs, including cell growth and inhibition of angiogenesis. In particular, we demonstrated that TIMP-3 overexpression using gene transfer induces apoptosis in a variety of cell types and can inhibit vascular neointima formation in vivo. However, little is know about the mechanisms underlying TIMP-3-mediated apoptosis. Here, using both purified recombinant proteins and novel adenoviral vectors we demonstrate that the prodeath domain of TIMP-3 is located within the N-terminal three loops of TIMP-3. Although both wild type and N-terminal TIMP-3 proteins promoted apoptosis, a T-2/T-3 chimera, in which the N-terminal three loops of TIMP-3 are replaced by those of TIMP-2, failed to induce cell death. Furthermore, a point mutation at residue 1 of TIMP-3 totally abolished MMP-inhibitory activity of TIMP-3 and also failed to promote apoptosis. This study demonstrates, using multiple apoptosis assays, that the prodeath function of TIMP-3 is located within the N-terminal three loops and the presence of functional metalloproteinase-inhibitory activity is associated with the induction of apoptosis.

ADAM28 is overexpressed in human non-small cell lung carcinomas and correlates with cell proliferation and lymph node metastasis

ADAM (a disintegrin and metalloproteinases) are a recently discovered gene family of proteins with sequence similarity to the reprolysin family of snake venom metalloproteinases, and about one‐third of the family members have the catalytic site consensus sequence in their metalloproteinase domains. We screened the mRNA expression of 11 different ADAM species with putative metalloproteinase activity in human non‐small cell lung carcinomas by RT‐PCR, and found that prototype membrane‐anchored ADAM28 (ADAM28m) and secreted ADAM28 (ADAM28s) are predominantly expressed in the carcinoma tissues. Real‐time quantitative PCR demonstrated that the expression levels of ADAM28m and ADAM28s are significantly 16.8‐fold and 9.0‐fold higher in the carcinomas than in the non‐carcinoma tissues, respectively. In addition, the expression levels of ADAM28m and ADAM28s were significantly higher in the carcinomas with >30 mm in diameter than in those ≦30 mm. The expression levels were also significantly higher in the carcinomas with lymph node metastasis than in those without metastasis. MIB1‐positive cell index of the carcinomas had a direct correlation with the expression levels of ADAM28m and ADAM28s (r = 0.667, p < 0.001 and r = 0.535, p < 0.01, respectively). In situ hybridization and immunohistochemistry demonstrated that ADAM28 is expressed predominantly in the carcinoma cells. Immunoblot analysis showed the activated form of ADAM28 in the carcinoma tissues. These data demonstrate for the first time that ADAM28 is overexpressed and activated in human non‐small cell lung carcinomas, and suggest the possibility that ADAM28 plays a role in cell proliferation and progression of the human lung carcinomas.

Synthesis and evaluation of δ-lactams (piperazones) as elastase inhibitors

A series of monocyclic δ-lactams (piperazones) was prepared and analysed as inhibitors of porcine pancreatic elastase and human neutrophil elastase.

Enzyme Accessibility and Solid Supports: Which Molecular Weight Enzymes Can Be Used on Solid Supports? An Investigation Using Confocal Raman Microscopy

The accessibility of various solid supports (TentaGel, PEGA 1900, and beaded controlled pore glasses (CPGs)) to a range of enzymes was investigated. The different beaded materials were loaded with the peptide 4-cyanobenzamide-Gly-Pro-Leu-Gly-Leu-Phe-Ala-Arg-OH and incubated with the enzymes MMP-12 (22 kDa), thermolysin (35 kDa), MMP-13 (42.5 kDa), clostridium collagenase (68 kDa), and NEP (90 kDa). The absence/presence of the cyano stretching frequency was measured by means of confocal Raman microscopy. It was found that none of the investigated enzymes could enter the polymer matrices of TentaGel. PEGA 1900 was compatible only with the two smallest enzymes, while beaded CPG was successful even with NEP (90 kDa), proving its superiority over other materials in terms of bio-compatibility.

TIMP-3 Inhibition of ADAMTS-4 (Aggrecanase-1) Is Modulated by Interactions between Aggrecan and the C-terminal Domain of ADAMTS-4

ADAMTS-4 (aggrecanase-1) is a glutamyl endopeptidase capable of generating catabolic fragments of aggrecan analogous to those released from articular cartilage during degenerative joint diseases such as osteoarthritis. Efficient aggrecanase activity requires the presence of sulfated glycosaminoglycans attached to the aggrecan core protein, implying the contribution of substrate recognition/binding site(s) to ADAMTS-4 activity. In this study, we developed a sensitive fluorescence resonance energy transfer peptide assay with a Km in the 10 μm range and utilized this assay to demonstrate that inhibition of full-length ADAMTS-4 by full-length TIMP-3 (a physiological inhibitor of metalloproteinases) is enhanced in the presence of aggrecan. Our data indicate that this interaction is mediated largely through the binding of glycosaminoglycans (specifically chondroitin 6-sulfate) of aggrecan to binding sites in the thrombospondin type 1 motif and spacer domains of ADAMTS-4 to form a complex with an improved binding affinity for TIMP-3 over free ADAMTS-4. The results of this study therefore indicate that the cartilage environment can modulate the function of enzyme-inhibitor systems and could have relevance for therapeutic approaches to aggrecanase modulation.

The C-terminal domains of TACE weaken the inhibitory action of N-TIMP-3

Tumor necrosis factor‐α converting enzyme (TACE) is an ADAM ( isintegrin nd etalloproteinases) that comprises an active catalytic domain and several C‐terminal domains. We compare the binding affinity and association rate constants of the N‐terminal domain form of wild‐type tissue inhibitor of metalloproteinase (TIMP‐3; N‐TIMP‐3) and its mutants against full‐length recombinant TACE and the truncated form of its catalytic domain. We show that the C‐terminal domains of TACE substantially weaken the inhibitory action of N‐TIMP‐3. Further probing with hydroxamate inhibitors indicates that both forms of TACE have similar active site configurations. Our findings highlight the potential role of the C‐terminal domains of ADAM proteinases in influencing TIMP interactions.