Defective glycosylation of decorin and biglycan, altered collagen structure, and abnormal phenotype of the skin fibroblasts of an Ehlers–Danlos syndrome patient carrying the novel Arg270Cys substitution in galactosyltransferase I (β4GalT-7)

Abstract

The Ehlers-Danlos syndrome (EDS) is a heterogeneous group of connective tissue disorders affecting skin and joint function. Molecular defects in extracellular matrix proteins, including collagen (type I, III, and V) and tenascin X are associated with different forms of EDS. Compound heterozygous mutations in the B4GALT7 gene, resulting in aberrant glycosylation of the dermatan sulfate proteoglycan decorin, had been described in a single patient affected with the progeroid form of EDS. We have studied the molecular phenotype of decorin, biglycan, and collagen type I containing fibrils in skin fibroblasts of a patient carrying the novel homozygous C808T point mutation in the B4GALT7 gene, which causes an Arg270Cys substitution in beta4GalT-7. Compared to control fibroblasts, galactosyltransferase activity in beta4GalT-7(Arg270Cys) cells was approximately three times reduced over a temperature range of 25-41 degrees C. Pulse-chase experiments and confocal microscopy demonstrated that synthesis and secretion of decorin were normal in beta4GalT-7(Arg270Cys) cells. However, about 50% of decorin were synthesized as a protein core in addition to its proteoglycan form. Biglycan was found in a monoglycanated form in addition to its mature form. Glycosaminoglycan chains were of the dermatan/chondroitin sulfate type both in beta4GalT-7(Arg270Cys) and control cells, and epimerization was reduced for decorin and biglycan. Compared to control cells, beta4GalT-7(Arg270Cys) cells showed altered, highly spread or stretched phenotypes and decreased proliferation rates. At the ultrastructural level, an intracellular accumulation of multiple secondary lysosomes and degenerative vacuoles was seen in beta4GalT-7(Arg270Cys) cells. Furthermore, the collagen suprastructures were altered in the beta4GalT-7(Arg270Cys) cells. The reduced beta4GalT-7 activity resulting in defective glycosylation of decorin and biglycan may be responsible for the complex molecular pathology in beta4GalT-7 deficient EDS patients, given the role of these proteoglycans in bone formation, collagen fibrillogenesis, and skeletal muscle development.

HER-2/neu-mediated Down-regulation of Biglycan Associated with Altered Growth Properties

“…The molecular and functional reasons are unknown until now. We suppose that this isoform is the same as the previously described monoglycanated isoform in skin fibroblasts of a patient with Ehlers-Danlos syndrome, whereas healthy control fibroblasts lack this isoform (42). Transgenic overexpression of Bgn inhibited the HER-2/neuinduced cell proliferation, anchorage-independent growth on poly-Heme-coated cell culture dishes, and migration.…”

Bone Dysplasia as a Key Feature in Three Patients with a Novel Congenital Disorder of Glycosylation (CDG) Type II Due to a Deep Intronic Splice Mutation in TMEM165

“…Skeletal manifestations are an important/predominant part of the phenotype in only about 20 % of the known CDG: EXT1/EXT2-CDG (Jennes et al 2009), B4GALT7 (Seidler et al 2006), B3GAT3-CDG (Baasanjar et al 2011), GALNT3-CDG (Chefetz and Sprecher 2009), SLC35D1-CDG (Hiraoka et al 2007), LFNG-CDG (Sparrow et al 2006), PIGV-CDG (Horn et al 2011), autosomal recessive cerebrocostomandibular like syndrome due to COG1-CDG (Zeevaert et al 2009), and ATP6V0A2-CDG (Guillard et al 2009). The spectrum of these skeletal manifestations is very broad which can be explained by the fact that glycosylation is an important posttranslational modification of numerous proteins, including extracellular matrix proteins and proteins involved in bone metabolism, for example, collagen I (Coman et al 2007) and FGFR-3 (Winterpacht et al 2000).…”

miR-145-dependent targeting of Junctional Adhesion Molecule A and modulation of fascin expression are associated with reduced breast cancer cell motility and invasiveness

“…Cell proliferation was determined by MTT assay as described previously (Seidler et al, 2006). 48, 72 or 96 h after microRNA precursor transfection, 10 000 MDA-MB-231 cells were seeded in 96-well plates and cultured for 24 h, followed by 24 h incubation in the presence of MTT, lysis and optical density measurement at 595 nm in a microplate reader.…”