title: A protein kinase C/Ras/ERK signaling pathway activates myeloid fibronectin receptors by altering beta1 integrin sialylation.
abstract: Here we report that myeloid cells differentiating along the monocyte/macrophage lineage down-regulate the ST6Gal-I sialyltransferase via a protein kinase C/Ras/ERK signaling cascade. In consequence, the beta1 integrin subunit becomes hyposialylated, which stimulates the ligand binding activity of alpha5beta1 fibronectin receptors. Pharmacologic inhibitors of protein kinase C, Ras, and MEK, but not phosphoinositide 3-kinase, block ST6Gal-I down-regulation, integrin hyposialylation, and fibronectin binding. In contrast, constitutively active MEK stimulates these same events, indicating that ERK is both a necessary and sufficient activator of hyposialylation-dependent integrin activation. Consistent with the enhanced activity of hyposialylated cell surface integrins, purified alpha5beta1 receptors bind fibronectin more strongly upon enzymatic desialylation, an effect completely reversed by resialylation of these integrins with recombinant ST6Gal-I. Finally, we have mapped the N-glycosylation sites on the beta1 integrin to better understand the potential effects of differential sialylation on integrin structure/function. Notably, there are three N-glycosylated sites within the beta1 I-like domain, a region that plays a crucial role in ligand binding. Our collective results suggest that variant sialylation, induced by a specific signaling cascade, mediates the sustained increase in cell adhesiveness associated with monocytic differentiation.
authors.affiliation: Department of Pathology, University of Alabama at Birmingham, 35294, USA.
authors.forename: Eric C
authors.initials: EC
authors.lastname: Seales
authors.forename: Faheem M
authors.initials: FM
authors.lastname: Shaikh
authors.forename: Alencia V
authors.initials: AV
authors.lastname: Woodard-Grice
authors.forename: Pooja
authors.initials: P
authors.lastname: Aggarwal
authors.forename: Alexis C
authors.initials: AC
authors.lastname: McBrayer
authors.forename: Kristin M
authors.initials: KM
authors.lastname: Hennessy
authors.forename: Susan L
authors.initials: SL
authors.lastname: Bellis
mesh_terms: D015536:Down-Regulation; D048049:Extracellular Signal-Regulated MAP Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D015971:Gene Expression Regulation, Enzymologic; D006801:Humans; D039081:Integrin alpha5beta1 / Q000378:metabolism*; D019012:Integrin beta1 / Q000378:metabolism*; D020930:MAP Kinase Kinase Kinases / Q000235:genetics / Q000378:metabolism; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000378:metabolism*; D012799:Sialyltransferases / Q000378:metabolism; D015398:Signal Transduction; D013755:Tetradecanoylphorbol Acetate; D020298:U937 Cells; D018631:ras Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000094802:beta-D-Galactoside alpha 2-6-Sialyltransferase
chemical_list: D039081:Integrin alpha5beta1; D019012:Integrin beta1; D012799:Sialyltransferases; D011493:Protein Kinase C; D048049:Extracellular Signal-Regulated MAP Kinases; D020930:MAP Kinase Kinase Kinases; D018631:ras Proteins; D013755:Tetradecanoylphorbol Acetate; D000094802:beta-D-Galactoside alpha 2-6-Sialyltransferase