Expression of silicatein and collagen genes in the marine sponge Suberites domuncula is controlled by silicate and myotrophin

Abstract

The major skeletal elements in the (Porifera) sponges, are spicules formed from inorganic material. The spicules in the Demospongiae class are composed of hydrated, amorphous silica. Recently an enzyme, silicatein, which polymerizes alkoxide substrates to silica was described from the sponge Tethya aurantia. In the present study the cDNA encoding silicatein was isolated from the sponge Suberites domuncula. The deduced polypeptide comprises 331 amino acids and has a calculated size of M r 36 306. This cDNA was used as a probe to study the potential role of silicate on the expression of the silicatein gene. For these studies, primmorphs, a special form of aggregates composed of proliferating cells, have been used. It was found that after increasing the concentration of soluble silicate in the seawater medium from around 1 mm to approximately 60 mm, this gene is strongly upregulated. Without additional silicate only a very weak expression could be measured. Because silica as well as collagen are required for the formation of spicules, the expression of the gene encoding collagen was measured in parallel. It was also found that the level of transcripts for collagen strongly increases in the presence of 60 mm soluble silicate. In addition, it is demonstrated that the expression of collagen is also upregulated in those primmorphs which were treated with recombinant myotrophin obtained from the same sponge. Myotrophin, however, had no effect on the expression of silicatein. From these data we conclude that silicate influences the expression of the enzyme silicatein and also the expression of collagen, (via the mediator myotrophin).

Identification of a silicatein(-related) protease in the giant spicules of the deep-sea hexactinellidMonorhaphis chuni

“…In the present study we found that the total extract as well as the extract from separated lamellae of these spicules contains a silicatein(-related) molecule, with respect to size, post-translation modification and enzyme activity. SDS-PAGE showed that characteristic lowmolecular mass protein(s) of 27·kDa exist in the spicules, which match in size with silicateins from demosponges (Cha et al, 1999;Krasko et al, 2000;Müller et al, 2007a) and correspond to the mature enzyme. As known from the different forms of the silicateins in T. aurantium (Cha et al, 1999) or S. domuncula (Krasko et al, 2000;Müller et al, 2003), these molecules are expressed/translated as a pro-enzyme (signal peptide-propeptidemature enzyme: 36.3·kDa) and processed via the 34.7·kDa form (propeptide-mature enzyme) to the 23·kDa mature enzyme.…”

“…The responsible enzyme, silicatein, was first described by the group of Morse in the marine demosponge Tethya aurantium (Cha et al, 1999) and subsequently also identified in other demosponges, most prominently in Suberites domuncula (Krasko et al, 2000). The genes of two isoforms of silicateins, silicatein-␣ and silicatein-␤ (Cha et al, 1999), have been identified in marine demosponges, and a third type, silicatein-␥, has been identified but not yet at the gene level (Shimizu et al, 1998).…”

“…The silicateins undergo post-translational modification, primarily phosphorylation (Müller et al, 2005). The polypeptide sequences of the silicateins share high sequence similarity with cathepsin L (Cha et al, 1999;Krasko et al, 2000); the active centre of silicatein differs from that of cathepsin L by only one amino acid (catalytic triad is Ser-HisAsn in silicatein and Cys-His-Asn in cathepsins). Cathepsins belong to the cysteine proteinases which can be effectively Silicatein-related enzyme activity inhibited by E-64 [L-trans-epoxysuccinyl-leucylamido(4-guanidino)butane] (Barrett et al, 1982) (reviewed in Barrett et al, 2002); E-64 does not affect cysteine residues in other enzymes, including the serine proteinases.…”

Magnetic resonance imaging of the siliceous skeleton of the demosponge Lubomirskia baicalensis

“…The center of these spicules is formed by an axial canal which contains an axial Wlament (Kaluzhnaya et al, 2005a) composed of silicatein (Kaluzhnaya et al, 2005b), the enzyme that is involved in the polymerization of silica (Cha et al, 1999;Krasko et al, 2000). An earlier study with the sponge Tethya aurantium (Weaver and Morse, 2003) reported that bifurcation of the axial Wlament precisely results in an unusual dichotomous morphology of the spicules.…”

“…Silicatein belongs to the family of cathepsin L proteases (Cha et al, 1999) and is involved in the condensation/polymerization reaction of silica (Cha et al, 1999;Krasko et al, 2000).…”