title: Latency-associated peptide of transforming growth factor-β1 is not subject to physiological mannose phosphorylation.
abstract: Latent TGF-β1 was one of the first non-lysosomal glycoproteins reported to bear mannose 6-phosphate (Man-6-P) residues on its N-glycans. Prior studies have suggested that this sugar modification regulates the activation of latent TGF-β1 by allowing it to bind cell surface-localized Man-6-P receptors. Man-6-P has also been proposed as an anti-scarring therapy based on its ability to directly block the activation of latent TGF-β1. A complete understanding of the physiological relevance of latent TGF-β1 mannose phosphorylation, however, is still lacking. Here we investigate the degree of mannose phosphorylation on secreted latent TGF-β1 and examine its Man-6-P-dependent activation in primary human corneal stromal fibroblasts. Contrary to earlier reports, minimal to no Man-6-P modification was found on secreted and cell-associated latent TGF-β1 produced from multiple primary and transformed cell types. Results showed that the inability to detect Man-6-P residues was not due to masking by the latent TGF-β1-binding protein (LTBP). Moreover, the efficient processing of glycans on latent TGF-β1 to complex type structures was consistent with the lack of mannose phosphorylation during biosynthesis. We further demonstrated that the conversion of corneal stromal fibroblast to myofibroblasts, a well known TGF-β1-dependent process, was not altered by Man-6-P addition when latent forms of this growth factor were present. Collectively, these findings indicate that Man-6-P-dependent effects on latent TGF-β1 activation are not mediated by direct modification of its latency-associated peptide.
authors.affiliation: Complex Carbohydrate Research Center, University of Georgia, Athens, Georgia 30602, USA.
authors.forename: Jarrod
authors.initials: J
authors.lastname: Barnes
authors.forename: Debra
authors.initials: D
authors.lastname: Warejcka
authors.forename: Jennifer
authors.initials: J
authors.lastname: Simpliciano
authors.forename: Sally
authors.initials: S
authors.lastname: Twining
authors.forename: Richard
authors.initials: R
authors.lastname: Steet
mesh_terms: D000818:Animals; D016466:CHO Cells; D003315:Cornea / Q000166:cytology / Q000378:metabolism*; D006224:Cricetinae; D003412:Cricetulus; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D020014:K562 Cells; D053779:Latent TGF-beta Binding Proteins / Q000235:genetics / Q000378:metabolism*; D008358:Mannose / Q000235:genetics / Q000378:metabolism*; D008360:Mannosephosphates / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation / Q000502:physiology; D053773:Transforming Growth Factor beta1 / Q000235:genetics / Q000378:metabolism*
chemical_list: D053779:Latent TGF-beta Binding Proteins; D008360:Mannosephosphates; D053773:Transforming Growth Factor beta1; C027693:mannose-6-phosphate; D008358:Mannose