Dataset Information

O-fucosylation of Thrombospondin Type I Repeats on Thrombospondin 1 is dispensable for trafficking to Platelets

ABSTRACT: Thrombospondin 1 (THBS1) is a secreted extracellular matrix glycoprotein that regulates a variety of cellular and physiological processes. THBS1’s diverse functions are attributed to interactions between the modular domains of THBS1 with an array of proteins found in the extracellular matrix. THBS1’s three Thrombospondin Type 1 Repeats (TSRs) domains are modified with O-linked glucose-fucose disaccharide and C-mannose. It is unknown whether these modifications impact trafficking and/or function of THBS1 in vivo. The O-fucose is added by Protein O-fucosyltransferase 2 (POFUT2) and is sequentially extended to the disaccharide by β3glucosyltransferase (B3GLCT). The C-mannose is added by one or more of four C-mannosyltransferases. O-fucosylation by POFUT2/B3GLCT in the endoplasmic reticulum has been proposed to play a role in quality control by locking TSR domains into their 3-dimensional fold, allowing for proper secretion of many O-fucosylated substrates. Prior studies showed the siRNA knockdown of POFUT2 in HEK293T cells blocked secretion of TSRs 1-3 from THBS1. Here we demonstrated that secretion of THBS1 TSRs 1-3 was not reduced by CRISPR-Cas9-mediated knockout of POFUT2 in HEK293T cells and demonstrated that knockout of Pofut2 or B3glct in mice did not reduce trafficking of endogenous THBS1 to platelet secretory granules, a major site of THBS1 expression. Additionally, we demonstrated that all three TSRs from platelet THBS1 were highly C-mannosylated, which has been shown to stabilize TSRs in vitro. Combined these results suggested that POFUT2 substrates with TSRs that are also modified by C-mannose may be less susceptible to trafficking defects resulting from loss of the glucose-fucose disaccharide.

INSTRUMENT(S): Q Exactive HF

ORGANISM(S): Mus Musculus (mouse)

TISSUE(S): Blood Platelet

SUBMITTER: Steven Berardinelli

LAB HEAD: Robert S. Haltiwanger

PROVIDER: PXD037158 | Pride | 2023-02-02

REPOSITORIES: Pride

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O-fucosylation of thrombospondin type I repeats is dispensable for trafficking thrombospondin 1 to platelet secretory granules.

Berardinelli Steven J SJ Sillato Andrew R AR Grady Richard C RC Neupane Sanjiv S Ito Atsuko A Haltiwanger Robert S RS Holdener Bernadette C BC

Glycobiology 20230501 4

Thrombospondin 1 (THBS1) is a secreted extracellular matrix glycoprotein that regulates a variety of cellular and physiological processes. THBS1's diverse functions are attributed to interactions between the modular domains of THBS1 with an array of proteins found in the extracellular matrix. THBS1's three Thrombospondin type 1 repeats (TSRs) are modified with O-linked glucose-fucose disaccharide and C-mannose. It is unknown whether these modifications impact trafficking and/or function of THBS1 ...[more]

PMID: 36721988

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Project description:A disintegrin-like and metalloprotease domain with thrombospondin type 1 repeats-like 2 (ADAMTSL2) is a matricellular protein that interacts with latent TGF-b binding protein 1 and fibrillin-1. ADAMTSL2 mutations cause an autosomal recessive connective tissue disorder named geleophysic dysplasia 1 (GPHYSD1, OMIM #231050), which is characterized by short stature, small hands and feet, and cardiac defects. ADAMTSL2 contains seven thrombospondin type-1 repeats (TSRs), six of which contain the consensus sequence for serine or threonine glycosylation by protein O-fucosyltransferase 2 (POFUT2). O-fucose modified TSRs are subsequently elongated to a Glucose1-3Fucose (GlcFuc) disaccharide by b3-glucosyltransferase (B3GLCT). B3GLCT mutations cause Peters Plus Syndrome (PTRPLS, OMIM #261540), which is characterized by skeletal defects similar to those of GPHYSD1. Several ADAMTSL2 TSRs have consensus sequences for C-mannosylation, and one TSR contains a sequon for N-glycosylation that overlaps with an O-fucosylation site. Six reported GPHYSD1 mutations occur within the TSRs and two lie near O-fucosylation sites. To investigate the effects of TSR glycosylation on ADAMTSL2 function, we used mass spectrometry to identify glycan modifications at the predicted consensus sequences. We found that most TSRs were modified with the GlcFuc disaccharide at high stoichiometry at O-fucosylation sites and variable mannose stoichiometry at C-mannosylation sites. Loss of ADAMTSL2 secretion in POFUT2 knockout but not in B3GLCT knockout cells suggested that impaired ADAMTSL2 secretion is not responsible for skeletal defects in PTRPLS patients lacking B3GLCT. In contrast, secretion of mouse ADAMTSL2 carrying GPHYSD1 mutations (S641L in TSR3 and G817R in TSR6) was significantly reduced in HEK293T cells. Moreover, S641L eliminated O-fucosylation of TSR3. Combined these results provide strong evidence that developmental abnormalities in GPHYSD1 patients with this mutation are caused by loss of O-fucosylation on TSR3 and impaired ADAMTSL2 secretion.

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