A 35-kDa Protein Is the Basic Unit of the Core from the 2 × 104-kDa Aggregation Factor Responsible for Species-specific Cell Adhesion in the Marine Sponge Microciona prolifera

Xavier Fernàndez-Busquets,Richard A Kammerer,Max M Burger

doi:10.1074/jbc.271.38.23558

Xavier Fernàndez-Busquets, Richard A Kammerer + Show 1 more

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https://doi.org/10.1074/jbc.271.38.23558

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Abstract

Dissociated sponge cells quickly reaggregate in a species-specific manner, differentiate, and reconstruct tissue, providing a very handy system to investigate the molecular basis of more complex intercellular recognition processes. Species-specific cell adhesion in the marine sponge Microciona prolifera is mediated by a supramolecular complex with a Mr = 2 x 10(7), termed aggregation factor. Guanidinium hydrochloride/cesium chloride dissociative gradients and rhodamine B isothiocyanate staining indicated the presence of several proteins with different degrees of glycosylation. Hyaluronate has been found to be associated with the aggregation factor. Chemical deglycosylation revealed a main component accounting for nearly 90% of the total protein. The cDNA-deduced amino acid sequence predicts a 35-kDa protein (MAFp3), the first sponge aggregation factor core protein ever described. The open reading frame is uninterrupted upstream from the amino terminus of the mature protein, and the deduced amino acid sequence for this region has been found to contain a long stretch sharing homology with the Na+-Ca2+ exchanger protein. A putative hyaluronic acid binding domain and several putative N- and O-glycosylation signals are present in MAFp3, as well as eight cysteines, some of them involved in intermolecular disulfide bridges. Northern blot data suggest variable expression, and Southern blot analysis reveals the presence of other related gene sequences. According to the respective molecular masses, one aggregation factor molecule would contain about 300 MAFp3 units, suggesting that sponge cell adhesion might be based on the assembly of multiple small glycosylated protein subunits.

Highlights

Sponges have been traditionally used as models to study cell adhesion, since their rather loose and porous extracellular matrix allows a mild cell dissociation and the recovery of intercellular structures in virtually native state
Gation factors are proteoglycan-like molecules showing either a linear appearance (Halichondria, Haliclona, Terpios) or a closed, sunburst-like morphology (Microciona, Geodia). Their active participation in species-specific cell-cell and cell-matrix interactions (Gramzow et al, 1988a) is in contrast to the rather passive mechanical functions generally ascribed to proteoglycans, growing evidence is accumulating in favor of their relevant role in differentiation and proliferation of cells (Ruoslahti, 1988)
Variability in the glycosaminoglycan moiety of proteoglycans seems to correlate with changes in adhesiveness of the cells to other cells or to the substrate (Sanderson et al, 1994; Roughley et al, 1993), much in the same way as it has been described for the neural cell-adhesion molecule, where electrostatic interactions between charged glycosaminoglycan chains are thought to modulate the strength of cell-cell interaction (Rothbard et al, 1982)

Summary

Introduction

Sponges have been traditionally used as models to study cell adhesion, since their rather loose and porous extracellular matrix allows a mild cell dissociation and the recovery of intercellular structures in virtually native state. Gation factors are proteoglycan-like molecules showing either a linear appearance (Halichondria, Haliclona, Terpios) or a closed, sunburst-like morphology (Microciona, Geodia). Their active participation in species-specific cell-cell and cell-matrix interactions (Gramzow et al, 1988a) is in contrast to the rather passive mechanical functions generally ascribed to proteoglycans, growing evidence is accumulating in favor of their relevant role in differentiation and proliferation of cells (Ruoslahti, 1988). MAF-promoted, species-specific sponge cell adhesion involves 1) a Ca2ϩ-dependent MAF self-interaction site, and 2) a Ca2ϩindependent MAF-cell binding (Jumblatt et al, 1980). Polyvalent structures have been shown to be involved in both functional domains (Misevic and Burger, 1986; Misevic et al, 1987), and carbohydrate-carbohydrate interactions play a central role in MAF self-association activity (Misevic et al, 1987; Misevic and Burger, 1993). The nature of the main protein component of the aggregation factor core structure has remained elusive

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