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Articles by John R. Horton
Total Records ( 2 ) for John R. Horton
  Patricia A. Spears , M. Mitsu Suyemoto , Angela M. Palermo , John R. Horton , Terri S. Hamrick , Edward A. Havell and Paul E. Orndorff
  A Listeria monocytogenes bacteriophage was used to identify a phage-resistant Tn917 insertion mutant of the mouse-virulent listerial strain F6214-1. The mutant was attenuated when it was inoculated orally into female A/J mice and failed to replicate efficiently in cultured mouse enterocytes. Phage binding studies indicated that the mutant had a cell surface alteration that precluded phage attachment. All phenotypes associated with the mutation could be complemented in trans by a single open reading frame (ORF) that corresponded to the ORF interrupted by the Tn917 insertion. The complementation effected was, in all cases, at a level indistinguishable from that of the parent. The Tn917 insertion interrupted a gene that is predicted to encode a group 2 glycosyl transferase (provisionally designated glcV). A similar glcV gene is present in Listeria welshimeri and Listeria innocua and in some serotypes of L. monocytogenes. We speculate that the loss of the glcV product results in a defective phage receptor and that this alteration coincidentally influences a feature of the normal host-pathogen interaction required for virulence. Interestingly, the glcV lesion, while preventing phage attachment, did not alter the mutant`s ability to bind to cultured mouse enterocyte monolayers. Rather, the mutation appeared to alter a subsequent step in intracellular replication measured by a reduction in plaque-forming efficiency and plaque size. In vivo, the mutant was undetectable in the liver and spleen 48 h after oral inoculation. The mutation is significant in part because it is one of the few that produce attenuation when the mutant is delivered orally.
  Sean R. Stowell , Connie M. Arthur , Kristin A. Slanina , John R. Horton , David F. Smith and Richard D. Cummings
  Human galectins have distinct and overlapping biological roles in immunological homeostasis. However, the underlying differences among galectins in glycan binding specificity regulating these functions are unclear. Galectin-8 (Gal-8), a tandem repeat galectin, has two distinct carbohydrate recognition domains (CRDs) that may cross-link cell surface counter receptors. Here we report that each Gal-8 CRD has differential glycan binding specificity and that cell signaling activity resides in the C-terminal CRD. Full-length Gal-8 and recombinant individual domains (Gal-8N and Gal-8C) bound to human HL60 cells, but only full-length Gal-8 signaled phosphatidylserine (PS) exposure in cells, which occurred independently of apoptosis. Although desialylation of cells did not alter Gal-8 binding, it enhanced cellular sensitivity to Gal-8-induced PS exposure. By contrast, HL60 cell desialylation increased binding by Gal-8C but reduced Gal-8N binding. Enzymatic reduction in surface poly-N-acetyllactosamine (polyLacNAc) glycans in HL60 cells reduced cell surface binding by Gal-8C but did not alter Gal-8N binding. Cross-linking and light scattering studies showed that Gal-8 is dimeric, and studies on individual subunits indicate that dimerization occurs through the Gal-8N domain. Mutations of individual domains within full-length Gal-8 showed that signaling activity toward HL60 cells resides in the C-terminal domain. In glycan microarray analyses, each CRD of Gal-8 showed different binding, with Gal-8N recognizing sulfated and sialylated glycans and Gal-8C recognizing blood group antigens and polyLacNAc glycans. These results demonstrate that Gal-8 dimerization promotes functional bivalency of each CRD, which allows Gal-8 to signal PS exposure in leukocytes entirely through C-terminal domain recognition of polyLacNAc glycans.
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