Francesca A. Mercuri

Matrix metalloproteinases 19 and 20 cleave aggrecan and cartilage oligomeric matrix protein (COMP)

Matrix metalloproteinase (MMP)‐19 and MMP‐20 (enamelysin) are two recently discovered members of the MMP family. These enzymes are involved in the degradation of the various components of the extracellular matrix (ECM) during development, haemostasis and pathological conditions. Whereas MMP‐19 mRNA is found widely expressed in body tissues, including the synovium of normal and rheumatoid arthritic patients, MMP‐20 expression is restricted to the enamel organ. In this study we investigated the ability of MMP‐19 and MMP‐20 to cleave two of the macromolecules characterising the cartilage ECM, namely aggrecan and the cartilage oligomeric matrix protein (COMP). Both MMPs hydrolysed aggrecan efficiently at the well‐described MMP cleavage site between residues Asn341 and Phe342, as shown by Western blotting using neo‐epitope antibodies. Furthermore, the two enzymes cleaved COMP in a distinctive manner, generating a major proteolytic product of 60 kDa. Our results suggest that MMP‐19 may participate in the degradation of aggrecan and COMP in arthritic disease, whereas MMP‐20, due to its unique expression pattern, may primarily be involved in the turnover of these molecules during tooth development.

Type I collagen abrogates the clathrin-mediated internalization of membrane type 1 matrix metalloproteinase (MT1-MMP) via the MT1-MMP hemopexin domain.

Type I collagen (Col I)-stimulated matrix metalloproteinase-2 (MMP-2) activation via membrane type 1 MMP (MT1-MMP) involves both a transcriptional increase in MT1-MMP expression and a nontranscriptional response mediated by preexisting MT1-MMP. In order to identify which MT1-MMP domains were required for the nontranscriptional response, MCF-7 cells that lack endogenous MT1-MMP were transfected with either wild type or domain mutant MT1-MMP constructs. We observed that mutant constructs lacking the MT1-MMP cytoplasmic tail were able to activate MMP-2 in response to Col I but not a construct lacking the MT1-MMP hemopexin domain. Col I did not alter total MT1-MMP protein levels; nor did it appear to directly induce MT1-MMP oligomerization. Col I did, however, redistribute preexisting MT1-MMP to the cell periphery compared with unstimulated cells that displayed a more diffuse staining pattern. In addition, Col I blocked the internalization of MT1-MMP in a dynamin-dependent manner via clathrin-coated pit-mediated endocytosis. This mechanism of impaired internalization is different from that reported for concanavalin A, since it is not mediated by the cytoplasmic tail of MT1-MMP but rather by the hemopexin domain. In summary, upon Col I binding to its cell surface receptor, MT1-MMP internalization via clathrin-coated pit-mediated endocytosis is impaired through interactions with the hemopexin domain, thereby regulating its function and ability to activate MMP-2.

Mutations in the Interglobular Domain of Aggrecan Alter Matrix Metalloproteinase and Aggrecanase Cleavage Patterns EVIDENCE THAT MATRIX METALLOPROTEINASE CLEAVAGE INTERFERES WITH AGGRECANASE ACTIVITY

We have expressed G1-G2 mutants with amino acid changes at the DIPEN341↓342FFGVG and ITEGE373↓374ARGSV cleavage sites, in order to investigate the relationship between matrix metalloproteinase (MMP) and aggrecanase activities in the interglobular domain (IGD) of aggrecan. The mutation DIPEN341 to DIGSA341 partially blocked cleavage by MMP-13 and MMP-8 at the MMP site, while the mutation 342FFGVG to342GTRVG completely blocked cleavage at this site by MMP-1, -2, -3, -7, -8, -9, -13, -14. Each of the MMP cleavage site mutants, including a four-amino acid deletion mutant lacking residues ENFF343, were efficiently cleaved by aggrecanase, suggesting that the primary sequence at the MMP site had no effect on aggrecanase activity in the IGD. The mutation 374ARGSV to374NVYSV completely blocked cleavage at the aggrecanase site by aggrecanase, MMP-8 and atrolysin C but had no effect on the ability of MMP-8 and MMP-13 to cleave at the Asn341↓Phe bond. Susceptibility to atrolysin C cleavage at the MMP site was conferred in the DIGSA341 mutant but absent in the wild-type,342GTRVG, 374NVYSV, and deletion mutants. To further explore the relationship between MMP and aggrecanase activities, sequential digest experiments were done in which MMP degradation products were subsequently digested with aggrecanase andvice versa. Aggrecanase-derived G1 domains with ITEGE373 C termini were viable substrates for MMPs; however, MMP-derived G2 fragments were resistant to cleavage by aggrecanase. A 10-mer peptide FVDIPENFFG, which is a substrate analogue for the MMP cleavage site, inhibited aggrecanase cleavage at the Glu373↓Ala bond. This study demonstrates that MMPs and aggrecanase have unique substrate recognition in the IGD of aggrecan and suggests that sequences at the C terminus of the DIPEN341 G1 domain may be important for regulating aggrecanase cleavage.

RECOMBINANT HUMAN AGGRECAN G1-G2 EXHIBITS NATIVE BINDING PROPERTIES AND SUBSTRATE SPECIFICITY FOR MATRIX METALLOPROTEINASES AND AGGRECANASE

A recombinant human aggrecan G1-G2 fragment comprising amino acids Val1-Arg656 has been expressed in Sf21 cells using a baculovirus expression system. The recombinant G1-G2 (rG1-G2) was purified to homogeneity by hyaluronan-Sepharose affinity chromatography followed by high performance liquid chromatography gel filtration, and gave a single band of M r 90,000–95,000 by silver stain or immunoblotting with monoclonal antibody 1-C-6. The expressed G1-G2 bound to both hyaluronan and link protein indicating that the immunoglobulin-fold motif and proteoglycan tandem repeat loops of the G1 domain were correctly folded. Further analysis of secondary structure by rotary shadowing electron microscopy confirmed a double globe appearance, but revealed that the rG1-G2 was more compact than its native counterpart. The size of rG1-G2 by SDS-polyacrylamide gel electorphoresis was unchanged following digestion with keratanase and keratanase II and reduced by only 2–5 kDa following digestion with either O-glycosidase or N-glycosidase F. Recombinant G1-G2 was digested with purified matrix metalloproteinases (MMP), isolated aggrecanase, purified atrolysin C, or proteinases present in conditioned medium from cartilage explant cultures, and the products analyzed on SDS gels by silver stain and immunoblotting. Neoepitope antibodies recognizing the N-terminal F342FGVG or C-terminal DIPEN341 sequences were used to confirm MMP cleavage at the Asn341 ↓ Phe bond, while neoepitope antibodies recognizing the N-terminal A374RGSV or C-terminal ITEGE373 sequences were used to confirm aggrecanase cleavage at the Glu373 ↓ Ala bond. Cleavage at the authentic MMP and aggrecanase sites revealed that these proteinases have the same specificity for rG1-G2 as for native aggrecan. Incubation of rG1-G2 with conditioned medium from porcine cartilage cultures revealed that active soluble aggrecanase but no active MMPs, was released following stimulation with interleukin-1α or retinoic acid. Atrolysin C, which cleaves native bovine aggrecan at both the aggrecanase and MMP sites, efficiently cleaved rG1-G2 at the aggrecanase site but failed to cleave at the MMP site. In contrast, native glycosylated G1-G2 with or without keratanase treatment was cleaved by atrolysin C at both the aggrecanase and MMP sites. The results suggest that the presence or absence per se of keratan sulfate on native G1-G2 does not affect the activity of atrolysin C toward the two sites.

Inactivated Influenza Vaccine That Provides Rapid, Innate-Immune-System-Mediated Protection and Subsequent Long-Term Adaptive Immunity

ABSTRACT The continual threat to global health posed by influenza has led to increased efforts to improve the effectiveness of influenza vaccines for use in epidemics and pandemics. We show in this study that formulation of a low dose of inactivated detergent-split influenza vaccine with a Toll-like receptor 2 (TLR2) agonist-based lipopeptide adjuvant (R4Pam2Cys) provides (i) immediate, antigen-independent immunity mediated by the innate immune system and (ii) significant enhancement of antigen-dependent immunity which exhibits an increased breadth of effector function. Intranasal administration of mice with vaccine formulated with R4Pam2Cys but not vaccine alone provides protection against both homologous and serologically distinct (heterologous) viral strains within a day of administration. Vaccination in the presence of R4Pam2Cys subsequently also induces high levels of systemic IgM, IgG1, and IgG2b antibodies and pulmonary IgA antibodies that inhibit hemagglutination (HA) and neuraminidase (NA) activities of homologous but not heterologous virus. Improved primary virus nucleoprotein (NP)-specific CD8+ T cell responses are also induced by the use of R4Pam2Cys and are associated with robust recall responses to provide heterologous protection. These protective effects are demonstrated in wild-type and antibody-deficient animals but not in those depleted of CD8+ T cells. Using a contact-dependent virus transmission model, we also found that heterologous virus transmission from vaccinated mice to naive mice is significantly reduced. These results demonstrate the potential of adding a TLR2 agonist to an existing seasonal influenza vaccine to improve its utility by inducing immediate short-term nonspecific antiviral protection and also antigen-specific responses to provide homologous and heterologous immunity. IMPORTANCE The innate and adaptive immune systems differ in mechanisms, specificities, and times at which they take effect. The innate immune system responds within hours of exposure to infectious agents, while adaptive immunity takes several days to become effective. Here we show, by using a simple lipopeptide-based TLR2 agonist, that an influenza detergent-split vaccine can be made to simultaneously stimulate and amplify both systems to provide immediate antiviral protection while giving the adaptive immune system time to implement long-term immunity. Both types of immunity induced by this approach protect against vaccine-matched as well as unrelated virus strains and potentially even against strains yet to be encountered. Conferring dual functionality to influenza vaccines is beneficial for improving community protection, particularly during periods between the onset of an outbreak and the time when a vaccine becomes available or in scenarios in which mass vaccination with a strain to which the population is immunologically naive is imperative. The innate and adaptive immune systems differ in mechanisms, specificities, and times at which they take effect. The innate immune system responds within hours of exposure to infectious agents, while adaptive immunity takes several days to become effective. Here we show, by using a simple lipopeptide-based TLR2 agonist, that an influenza detergent-split vaccine can be made to simultaneously stimulate and amplify both systems to provide immediate antiviral protection while giving the adaptive immune system time to implement long-term immunity. Both types of immunity induced by this approach protect against vaccine-matched as well as unrelated virus strains and potentially even against strains yet to be encountered. Conferring dual functionality to influenza vaccines is beneficial for improving community protection, particularly during periods between the onset of an outbreak and the time when a vaccine becomes available or in scenarios in which mass vaccination with a strain to which the population is immunologically naive is imperative.