Lysosomal Sialidase (Neuraminidase-1) Is Targeted to the Cell Surface in a Multiprotein Complex That Facilitates Elastic Fiber Assembly

Abstract

We have established previously that the 67-kDa elastin-binding protein (EBP), identical to the spliced variant of ␤-galactosidase, acts as a recyclable chaperone that facilitates secretion of tropoelastin. (Hinek, A., Keeley, F. W., and Callahan, J. W. (1995) Exp. Cell Res. 220, 312-324). We now demonstrate that EBP also forms a cell surfacetargeted molecular complex with protective protein/cathepsin A and sialidase (neuraminidase-1), and provide evidence that this sialidase activity is a prerequisite for the subsequent release of tropoelastin. We found that treatment with sialidase inhibitors repressed assembly of elastic fibers in cultures of human skin fibroblasts, aortic smooth muscle cells, and ear cartilage chondrocytes and caused impaired elastogenesis in developing chick embryos. Fibroblasts derived from patients with congenital sialidosis (primary deficiency of neuraminidase-1) and galactosialidosis (secondary deficiency of neuraminidase-1) demonstrated impaired elastogenesis, which could be reversed after their transduction with neuraminidase-1 cDNA or after treatment with bacterial sialidase, which has a similar substrate specificity to human neuraminidase-1. We postulate that neuraminidase-1 catalyzes removal of the terminal sialic acids from carbohydrate chains of microfibrillar glycoproteins and other adjacent matrix glycoconjugates, unmasking their penultimate galactosugars. In turn, the exposed galactosugars interact with the galectin domain of EBP, thereby inducing the release of transported tropoelastin molecules and facilitating their subsequent assembly into elastic fibers.Mature elastic fibers and laminae present in the extracellular matrix of connective tissues of different organs and blood vessel walls are complex structures made of polymeric (insoluble) elastin in which polypeptide chains of tropoelastin are covalently cross-linked and assembled on a scaffold of 12-nm microfibrils consisting of several glycoproteins, e.g. fibrillins and microfibril-associated glycoproteins (1-11). Molecules of monomeric 70-kDa tropoelastin are synthesized by fibroblasts, chondrocytes, and smooth muscle cells and are secreted and properly aligned with one another for the subsequent lysyl oxidase-mediated cross-linking (12). The mechanisms governing tropoelastin secretion and assembly are not fully elucidated. The current data indicate that highly hydrophobic and non-glycosylated tropoelastin associates with several intracellular proteins that chaperone it through the intracellular compartments. Davis et al. (13) documented that, in the ergastoplasmic reticulum, tropoelastin binds to BiP and the peptidylprolyl cis,transisomerase FKPB65. Our immunohistochemical and biochemical studies have indicated that tropoelastin present in endosomal and Golgi compartments is escorted by the 67-kDa elastin-binding protein (EBP) 2 (14, 15), which protects tropoelastin from premature intracellular selfaggregation and an association with serine proteinases (16,17). We have established that, after delivering tropoelastin to...

Recombinant proteins produced into yolk of genetically manipulated chickens are partly sialylated in N-glycan

“…Ovarian follicular tissue expressed substantial level of NEU1, approximately 15 % of that in the liver. NEU1 is ubiquitously but differentially expressed in various cell types and its preferred substrates are both a2,3-and a2,6-sialyl linkage on glycoproteins, and the distribution of NEU1 is not restricted to lysosomes: it was detected on the cell surfaces of various cell types (Hinek et al 2006;Liang et al 2006). These are consistent with the notion that NEU1 decreased the sialic acid content of scFv/Fc during transfer to the yolk.…”

Contribution of sialidase NEU1 to suppression of metastasis of human colon cancer cells through desialylation of integrin β4

“…In addition to the glycoconjugate catabolism in lysosomes, recent reports revealed that NEU1 is involved in cellular signaling, including immune responses (Liang et al, 2006) and elastin receptor-mediated signal transduction through dynamical movement from lysosomes to cell-surface membranes (Hinek et al, 2006;Duca et al, 2007).…”

Interaction between the Elastin Peptide VGVAPG and Human Elastin Binding Protein

“…The elastin receptor complex is a critical actor of elastogenesis (9). In this highly regulated and coordinated phenomenon, it plays a dual role.…”

“…It is required for both elastin assembly (9) and elastin peptide signaling (20). Importantly, this activity requires the presence of EBP.…”