Matrix Metalloproteinases and Tissue Inhibitors of Metalloproteinases in Echinoderms: Structure and Possible Functions

Echinoderms are one of the most ancient groups of invertebrates. The study of their genomes has made it possible to conclude that these animals have a wide variety of matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs). The phylogenetic analysis shows that the MMPs and TIMPs underwent repeated duplication and active divergence after the separation of Ambulacraria (Echinodermata+Hemichordata) from the Chordata. In this regard the homology of the proteinases and their inhibitors between these groups of animals cannot be established. However, the MMPs of echinoderms and vertebrates have a similar domain structure. Echinoderm proteinases can be structurally divided into three groups-archetypal MMPs, matrilysins, and furin-activatable MMPs. Gelatinases homologous to those of vertebrates were not found in genomes of studied species and are probably absent in echinoderms. The MMPs of echinoderms possess lytic activity toward collagen type I and gelatin and play an important role in the mechanisms of development, asexual reproduction and regeneration. Echinoderms have a large number of genes encoding TIMPs and TIMP-like proteins. TIMPs of these animals, with a few exceptions, have a structure typical for this class of proteins. They contain an NTR domain and 10-12 conservatively located cysteine residues. Repeated duplication and divergence of TIMP genes of echinoderms was probably associated with an increase in the functional importance of the proteins encoded by them in the physiology of the animals.

Proteases from the regenerating gut of the holothurian Eupentacta fraudatrix

Four proteases with molecular masses of 132, 58, 53, and 47 kDa were detected in the digestive system of the holothurian Eupentacta fraudatrix. These proteases displayed the gelatinase activity and characteristics of zinc metalloproteinases. The 58 kDa protease had similar protease inhibitor sensitivity to that of mammalian matrix metalloproteinases. Zymographic assay revealed different lytic activities of all four proteases during intestine regeneration in the holothurian. The 132 kDa protease showed the highest activity at the first stage. During morphogenesis (stages 2-4 of regeneration), the highest activity was measured for the 53 and 58 kDa proteases. Inhibition of protease activity exerts a marked effect on regeneration, which was dependent on the time when 1,10-phenanthroline injections commenced. When metalloproteinases were inhibited at the second stage of regeneration, the restoration rates were decreased. However, such an effect proved to be reversible, and when inhibition ceased, the previous rate of regeneration was recovered. When protease activity is inhibited at the first stage, regeneration is completely abolished, and the animals die, suggesting that early activation of the proteases is crucial for triggering the regenerative process in holothurians. The role of the detected proteases in the regeneration processes of holothurians is discussed.

Characterization and expression of two matrix metalloproteinase genes during sea urchin development

Matrix metalloproteinases (MMPs) play an essential role in a variety of processes in development that require extracellular matrix remodeling and degradation. In this study, we characterize two MMPs from the sea urchin Strongylocentrotus purpuratus. These clones can both be identified as MMPs based on the presence of conserved domains such as the cysteine switch, zinc-binding, and hemopexin domains. In addition, both of these genes contain consensus furin cleavage sites and putative transmembrane domains, classifying them as membrane-type MMPs. We have named these clones SpMMP14 and SpMMP16 based on the vertebrate MMPs with which they share the greatest similarity. SpMMP14 is expressed in all cells from the egg to mesenchyme blastula stage embryo. Expression of this gene is strongest in the animal and vegetal poles early in gastrulation and in the animal pole only later in gastrulation. SpMMP16 is expressed at low levels in eggs. Expression of SpMMP16 becomes more pronounced in the vegetal pole region at the blastula and mesenchyme blastula stages and becomes confined to vegetal pole descendants, such as pigment cells, later in development. In the future, we hope to learn more about the possible functions of these genes in sea urchin development.

Zymogen activation and characterization of a major gelatin-cleavage activity localized to the sea urchin extraembryonic matrix

The hyaline layer (HL) is an apically located extracellular matrix (ECM) which surrounds the sea urchin embryo from the time of fertilization until metamorphosis occurs. While gelatin-cleavage activities were absent from freshly prepared hyaline layers, a dynamic pattern of activities developed in layers incubated at 15 or 37 degrees C in Millipore-filtered sea water (MFSW). Cleavage activities at 90, 55, 41, and 32 kDa were evident following incubation at either temperature. The activation pathway leading to the appearance of these species was examined to determine the minimum salt conditions required for processing and to establish precursor-product relationships. In both qualitative and quantitative assays, the purified 55 kDa gelatinase activity was inhibited by 1,10-phenanthroline (a zinc-specific chelator) and ethylenebis (oxyethylenenitrilo) tetraacetic acid (EGTA). Calcium reconstituted the activity of the EGTA-inhibited enzyme with an apparent dissociation constant (calcium) of 1.2 mM. Developmental substrate gel analysis was performed using various stage embryos. The 55 and 32 kDa species comigrated with gelatin-cleavage activities present in sea urchin embryos. Collectively, the results reported here document a zymogen activation pathway which generates a 55 kDa, gelatin-cleaving activity within the extraembryonic HL. This species displayed characteristics of the matrix metalloproteinase class of ECM modifying enzymes.

Characterization of matrix metalloprotease activities induced in the sea urchin extraembryonic matrix, the hyaline layer

Hyaline layers, freshly prepared from one-hour-old embryos, were devoid of gelatin-cleavage activity. However, upon storage at 4°C, gelatin-cleavage activities appeared; three species of apparent mol mass 94[Formula: see text]117-, 90-, and 45-kDa were seen. All three species required zinc for activity. Using gel-exclusion chromatography we separated the 94[Formula: see text]117-, and 90-kDa species from the 45-kDa activity. The two higher mol mass species were inhibited by ethylenebis (oxyethylenenitrilo) tetraacetic acid and the lost activity was restored by calcium. Reconstitution of activity occurred with an apparent dissociation constant (calcium) of 5 µM. The presence of millimolar concentrations of magnesium had a minimal inhibitory effect on activity. The thermal denaturation profile of the higher mol mass gelatin-cleavage activity was significantly different in the presence and absence of calcium. Stabilization of these activities against thermal denaturation at 60°C occurred with an apparent dissociation constant (calcium) of 0.6 mM. Magnesium had no significant effect on the thermal denaturation profile. Collectively, these results suggest at least two different modes of interaction between calcium and the higher mol mass gelatinases. These conclusions are discussed in the context of the high calcium and magnesium concentrations present in the sea water environment of the sea urchin embryo.Key words: sea urchin, embryo, matrix metalloprotease, calcium.

Effects of calcium and magnesium on a 41-kDa serine-dependent protease possessing collagen-cleavage activity

We report here the continued characterization of a 41-kDa protease expressed in the early stage of the sea urchin embryo. This protease was previously shown to possess both a gelatin-cleavage activity and an echinoderm-specific collagen-cleavage activity. In the experiments reported here, we have explored the biochemical nature of this proteolytic activity. Pepstatin A (an acidic protease inhibitor), 1,10-phenanthroline (a metalloprotease inhibitor), and E-64 (a thiol protease inhibitor) were without effect on the gelatin-cleavage activity of the 41-kDa species. Using a gelatin substrate gel zymographic assay, the serine protease inhibitors phenylmethylsulfonyl fluoride and benzamide appeared to partially inhibit gelatin-cleavage activity. This result was confirmed in a quantitative gelatin-cleavage assay using the water soluble, serine protease inhibitor [4-(2-aminoethyl)benzenesulfonylfluoride]. The biochemical character of this protease was further explored by examining the effects of calcium and magnesium, the major divalent cations present in sea water, on the gelatin-cleavage activity. Calcium and magnesium competed for binding to the 41-kDa collagenase/gelatinase, and prebound calcium was displaced by magnesium. Cleavage activity was inhibited by magnesium, and calcium protected the protease against this inhibition. These results identify calcium and magnesium as antagonistic agents that may regulate the proteolytic activity of the 41-kDa species.