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TAILS N-terminomics and proteomics reveal complex regulation of proteolytic cleavage by O-glycosylation.

ABSTRACT: Proteolytic processing is an irreversible post-translational modification functioning as a ubiquitous regulator of cellular activity. Protease activity is tightly regulated via control of gene expression, enzyme and substrate compartmentalization, zymogen activation, enzyme inactivation, and substrate availability. Emerging evidence suggests that proteolysis can also be regulated by substrate glycosylation and that glycosylation of individual sites on a substrate can decrease or, in rare cases, increase its sensitivity to proteolysis. Here, we investigated the relationship between site-specific, mucin-type (or GalNAc-type) O-glycosylation and proteolytic cleavage of extracellular proteins. Using in silico analysis, we found that O-glycosylation and cleavage sites are significantly associated with each other. We then used a positional proteomic strategy, terminal amine isotopic labeling of substrates (TAILS), to map the in vivo cleavage sites in HepG2 SimpleCells with and without one of the key initiating GalNAc transferases, GalNAc-T2, and after treatment with exogenous matrix metalloproteinase 9 (MMP9) or neutrophil elastase. Surprisingly, we found that loss of GalNAc-T2 not only increased cleavage, but also decreased cleavage across a broad range of other substrates, including key regulators of the protease network. We also found altered processing of several central regulators of lipid homeostasis, including apolipoprotein B and the phospholipid transfer protein, providing new clues to the previously reported link between GALNT2 and lipid homeostasis. In summary, we show that loss of GalNAc-T2 O-glycosylation leads to a general decrease in cleavage and that GalNAc-T2 O-glycosylation affects key regulators of the cellular proteolytic network, including multiple members of the serpin family.

SUBMITTER: King SL

PROVIDER: S-EPMC5961060 | biostudies-literature | 2018 May

REPOSITORIES: biostudies-literature

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TAILS N-terminomics and proteomics reveal complex regulation of proteolytic cleavage by <i>O</i>-glycosylation.

King Sarah L SL Goth Christoffer K CK Eckhard Ulrich U Joshi Hiren J HJ Haue Amalie D AD Vakhrushev Sergey Y SY Schjoldager Katrine T KT Overall Christopher M CM Wandall Hans H HH

The Journal of biological chemistry 20180328 20

Proteolytic processing is an irreversible post-translational modification functioning as a ubiquitous regulator of cellular activity. Protease activity is tightly regulated via control of gene expression, enzyme and substrate compartmentalization, zymogen activation, enzyme inactivation, and substrate availability. Emerging evidence suggests that proteolysis can also be regulated by substrate glycosylation and that glycosylation of individual sites on a substrate can decrease or, in rare cases, ...[more]

PMID: 29593093

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Project description:Proteolytic processing is an irreversible post-translational modification functioning as a ubiquitous regulator of cellular activity. Protease activity is tightly regulated by control of gene expression, compartmentalisation of enzyme and substrate, zymogen activation, enzyme inactivation, and substrate availability. Emerging evidence suggests that proteolysis can also be regulated by substrate glycosylation and that glycosylation of individual sites on a substrate can decrease, or in rare cases, increase its sensitivity to proteolysis. In the present study we investigated the relationship between site-specific O-glycosylation and proteolytic cleavage of extracellular proteins. By in silico analysis we found a significant association between O-glycosylation sites and cleavage sites. We then used a positional proteomic strategy, Terminal Amine Isotopic Labelling of Substrates (TAILS) to map in vivo cleavage sites in HepG2 cells with and without one of the key initiating GalNAc-transferases, GalNAc-T2. To reduce complexity, the comparison were performed in so-called SimpleCells. In these cells the Core 1 β3-galactosyltransferase-specific molecular chaperone (COSMC; C1GALT1C1) has been knocked out, resulting in global truncation of O-glycans leaving only the initial GalNAc. Surprisingly, we found that loss of GalNAc-T2 resulted in not only an increase in cleavage, but also a decrease in cleavage across a broad range of other substrates, including key regulators of the protease network. GALNT2 has previously been identified as a candidate gene for dyslipidaemia and has been shown to specifically glycosylate central regulators of lipid homeostasis, here we find altered processing of several of these regulators including Apolipoproteins B (ApoB) and the Phospholipid transfer protein (PLTP), providing new clues to the link between GALNT2 and lipid homeostasis. In contrast to the findings from the majority of previous studies, these results indicate that O-glycosylation can both decrease and increase substrate cleavage. We challenged this system with exogenous matrix metalloproteinase 9 (MMP9) and neutrophil elastase and observed substantial changes to the neutrophil elastase N-terminome, but no evidence for a similar role for MMP9. Overall, we show that loss of O-glycosylation leads to a general decrease in cleavage, that GalNAc-T2 O-glycosylation affects key regulators of the cellular proteolytic network, including multiple members of the Serpin family.

Project description:Enteroviruses encode proteinases that are essential for processing of the translated viral polyprotein. In addition, viral proteinases also target host proteins to manipulate cellular processes and evade innate antiviral responses to promote replication and infection. Although some host protein substrates of enterovirus proteinases have been identified, the full repertoire of targets remains unknown. We used a novel quantitative in vitro proteomics-based approach, termed terminal amine isotopic labeling of substrates (TAILS), to identify with high confidence 72 and 34 new host protein targets of poliovirus and coxsackievirus B3 (CVB3) 3C proteinases (3Cpros) in HeLa cell and cardiomyocyte HL-1 cell lysates, respectively. We validated a subset of candidate substrates that are targets of poliovirus 3Cproin vitro including three common protein targets, phosphoribosylformylglycinamidine synthetase (PFAS), hnRNP K, and hnRNP M, of both proteinases. 3Cpro-targeted substrates were also cleaved in virus-infected cells but not noncleavable mutant proteins designed from the TAILS-identified cleavage sites. Knockdown of TAILS-identified target proteins modulated infection both negatively and positively, suggesting that cleavage by 3Cpro promotes infection. Indeed, expression of a cleavage-resistant mutant form of the endoplasmic reticulum (ER)-Golgi vesicle-tethering protein p115 decreased viral replication and yield. As the first comprehensive study to identify and validate functional enterovirus 3Cpro substrates in vivo, we conclude that N-terminomics by TAILS is an effective strategy to identify host targets of viral proteinases in a nonbiased manner.IMPORTANCE Enteroviruses are positive-strand RNA viruses that encode proteases that cleave the viral polyprotein into the individual mature viral proteins. In addition, viral proteases target host proteins in order to modulate cellular pathways and block antiviral responses in order to facilitate virus infection. Although several host protein targets have been identified, the entire list of proteins that are targeted is not known. In this study, we used a novel unbiased proteomics approach to identify ?100 novel host targets of the enterovirus 3C protease, thus providing further insights into the network of cellular pathways that are modulated to promote virus infection.

Dataset Information

TAILS N-terminomics and proteomics reveal complex regulation of proteolytic cleavage by O-glycosylation.

Publications

TAILS N-terminomics and proteomics reveal complex regulation of proteolytic cleavage by <i>O</i>-glycosylation.

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