Proteoglycans are important components of cell plasma membranes and extracellular matrices of connective tissues. They consist of glycosaminoglycan chains attached to a core protein via a tetrasaccharide linkage, whereby the addition of the third residue is catalyzed by galactosyltransferase II (β3GalT6), encoded by B3GALT6. Homozygosity mapping and candidate gene sequence analysis in three independent families, presenting a severe autosomal-recessive connective tissue disorder characterized by skin fragility, delayed wound healing, joint hyperlaxity and contractures, muscle hypotonia, intellectual disability, and a spondyloepimetaphyseal dysplasia with bone fragility and severe kyphoscoliosis, identified biallelic B3GALT6 mutations, including homozygous missense mutations in family 1 (c.619G>C [p.Asp207His]) and family 3 (c.649G>A [p.Gly217Ser]) and compound heterozygous mutations in family 2 (c.323_344del [p.Ala108Glyfs(∗)163], c.619G>C [p.Asp207His]). The phenotype overlaps with several recessive Ehlers-Danlos variants and spondyloepimetaphyseal dysplasia with joint hyperlaxity. Affected individuals' fibroblasts exhibited a large decrease in ability to prime glycosaminoglycan synthesis together with impaired glycanation of the small chondroitin/dermatan sulfate proteoglycan decorin, confirming β3GalT6 loss of function. Dermal electron microcopy disclosed abnormalities in collagen fibril organization, in line with the important regulatory role of decorin in this process. A strong reduction in heparan sulfate level was also observed, indicating that β3GalT6 deficiency alters synthesis of both main types of glycosaminoglycans. In vitro wound healing assay revealed a significant delay in fibroblasts from two index individuals, pointing to a role for glycosaminoglycan defect in impaired wound repair in vivo. Our study emphasizes a crucial role for β3GalT6 in multiple major developmental and pathophysiological processes.

The heparan sulfate sulfotransferase 3-OST3A (HS3ST3A) is a novel tumor regulator and a prognostic marker in breast cancer Mao, X.; Gauche, C.; Coughtrie, M. W. H.; Bui, C.; Gulberti, S.; Merhi-Soussi, F. Citation for published version (APA):Mao, X., Gauche, C., Coughtrie, M. W. H., Bui, C., Gulberti, S., Merhi-Soussi, F., ... Fournel-Gigleux, S. (2016). The heparan sulfate sulfotransferase 3-OST3A (HS3ST3A) is a novel tumor regulator and a prognostic marker in breast cancer. Oncogene, 35, 5043-5055. DOI: 10.1038/onc.2016 General rights Copyright and moral rights for the publications made accessible in Discovery Research Portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from Discovery Research Portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain.• You may freely distribute the URL identifying the publication in the public portal. Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. Heparan sulfate (HS) proteoglycan chains are key components of the breast tumor microenvironment that critically influence the behavior of cancer cells. It is established that abnormal synthesis and processing of HS play a prominent role in tumorigenesis albeit mechanisms remain mostly obscure. HS function is mainly controlled by sulfotransferases, and here we report a novel cellular and pathophysiological significance for the 3--O--sulfotransferase 3--OST3A (HS3ST3A), catalyzing the final maturation step of HS, in breast cancer. We show that 3--OST3A is epigenetically repressed in all breast cancer cell lines of a panel representative of distinct molecular subgroups, except in HER2--positive (HER2+) SKBR3 cells. Epigenetic mechanisms involved both DNA methylation and histone modifications, producing different repressive chromatin environments depending on the cell molecular signature. Gain and loss of function experiments by cDNA and siRNA transfection revealed profound effects of 3--OST3A expression on cell behavior including apoptosis, proliferation, response to trastuzumab in vitro and tumor growth in xenografted mice. 3--OST3A exerted dual activities acting as tumor--suppressor in lumA--MCF--7 and triple negative--MDA--MB--231 cells, or as an oncogenic factor in HER2+--SKBR3 cells. Mechanistically, fluorescence--resonance energy transfer (FRET)--fluorescence--lifetime imaging microscopy (FLIM) experiments indicated that the effects of 3--OST3A in MCF--7 cells were mediated by altered interactions between HS and fibroblast growth factor--7 (FGF--7). Further, this interplay between HS and FGF--7 modulated downstream ERK, AKT and p38 cascades, suggesting that altering 3--O--sulfation affects FGFR...