Robertson, C. | bioRxiv Science

bioRxiv2019

The human UDP-galactose 4’-epimerase (GALE) is required for cell surface glycome structure and function

Glycan biosynthesis relies on nucleotide-sugars (NS), abundant metabolites that serve as monosaccharide donors for glycosyltransferases. In vivo, signal-dependent fluctuations in NS levels are required to maintain normal cell physiology and are dysregulated in disease, but how mammalian cells regulate NS levels and pathway flux remains largely uncharacterized. To address this knowledge gap, we examined uridine diphosphate (UDP)-galactose 4-epimerase (GALE), which interconverts two pairs of essential NSs. GALE deletion in human cells triggered major imbalances in its substrate NSs and consequent dramatic changes in glycolipids and glycoproteins, including a subset of integrins and the Fas death receptor. NS dysregulation also directly impacted cell signaling, as GALE-/- cells exhibit Fas hypoglycosylation and hypersensitivity to Fas ligand-induced apoptosis. Our results reveal a new role for GALE-mediated NS regulation in supporting death receptor signaling and may have implications for the molecular etiology of illnesses characterized by NS imbalances, including galactosemia and metabolic syndrome.

cell biology↗

bioRxiv2019

The microstructure of laminin-111 compensates for dystroglycan loss in functional differentiation of mammary epithelial cells

AbstractLaminin-111, an extracellular matrix (ECM) glycoprotein found in the basement membrane of mammary gland epithelia, is essential for lactation. In mammary epithelial cells, dystroglycan (Dg) is believed to be necessary for polymerization of laminin-111 into networks, thus we asked whether correct polymerization could compensate for Dg loss. Artificially polymerized laminin-111 and the laminin-glycoprotein mix Matrigel, both formed branching, spread networks with fractal dimensions from 1.7-1.8, whereas laminin-111 in media formed small aggregates without fractal properties (a fractal dimension of 2). In Dg knockout cells, either polymerized laminin-111 or Matrigel readily attached to the cell surface, whereas aggregated laminin-111 did not. In contrast, polymerized and aggregated laminin-111 bound similarly to Dg knock-ins. Both polymerized laminin-111 and Matrigel promoted cell rounding, clustering, formation of tight junctions, and expression of milk proteins, whereas aggregated Ln-1 did not attach to cells or promote functional differentiation. HighlightsO_LILaminin assembles into a fractal network when in presence of either the cell surface receptor dystroglycan or acidic glycoproteins or an acidic buffer. C_LIO_LIWhen this microstructure is recreated with an acidic treatment, laminin binds readily to dystroglycan null cells and induces functional differentiation of mammary epithelial cells. C_LI

bioengineering↗