Defining the altered glycoproteomic space of the early secretory pathway by class I mannosidase pharmacological inhibition.

N-glycosylation is a key process for various biological functions like protein folding, maturation and sorting for the conventional secretory compartment, cell-cell communication and immune response. This is usually accomplished by a complex system of mannosidases in which those from class I have an outstanding role, commonly involved in the early protein sorting associated to the Endoplasmic Reticulum (ER) in the N-glycan dependent quality control (ERQC) and ER-associated degradation (ERAD). Although these are vital processes in maintaining cellular homeostasis, large-scale analysis studies for this pool of molecules, further denoted as proteins from the early secretory pathway (ESP), were limited addressed. Here, using a custom workflow employing a combination of glycomics and deglycoproteomics analyses, using lectin affinity and selective Endoglycosidase H (Endo H) digestion, we scrutinize the steady-state oligomannosidic glycoprotein load and delineate ESP fraction in melanoma cells. All of these were assessed by applying our workflow for glycosite relative quantification of both the peptide chain and carbohydrate structure in cells with inhibited activity of class I mannosidases after kifunensine treatment. We found that most of the ESP are transient clients involved in cell communication via extracellular matrix, particularly integrin-mediated communication which adopt Man9 N-glycans in kifunensine-treated cells. Moreover, our results reveal that core-fucosylation is decreased subsequent inhibition of class I mannosidases and this could be explained by a general lower protein level of FUT8, the enzyme responsible for fucosylation. By comparing our data with results obtained following downregulation of a key mannosidase in misfolded protein degradation, we mapped both novel and previously suggested endogenous substrate candidates like PCDH2, HLA-B, LAMB2 or members of the integrin family of proteins such as ITGA1 and ITGA4, thus validating the findings obtained using our workflow regarding accumulation and characterization of ESP transitory members following mannosidase class I inhibition. This workflow and the associated dataset not only allowed us to investigate the oligomannosidic glycoprotein fraction but also to delineate differences mediated at glycosite-level upon kifunensine treatment and outline the potential associated cellular responses.

Dataset of human EDEM2 melanoma cells proteomics, affinity proteomics and deglycoproteomics.

EDEM2 (Endoplasmic reticulum Degradation-Enhancing alpha-Mannosidase-like protein 2) is one of the key-proteins suggested to be involved in the selection and degradation of misfolded proteins from the endoplasmic reticulum. The datasets discussed in this article are related to experiments covering affinity proteomics, label-free quantitative proteomics, deglycoproteomics and SILAC (Stable Isotope Labeling by Amino Acids in Cell Culture) proteomics data of A375 melanoma cells with modified expression of EDEM2. Our first aim was to affinity-enrich EDEM2 alongside its potential interaction partners and analyse the obtained samples by nanoLC-MS/MS to identify novel EDEM2 associated proteins. The dataset was substantiated by SDF (Sucrose Density Fractionation)-nanoLC-MS/MS experiments, in an integrated workflow to validate EDEM2 identified partners and corroborate these with previous data. Our second aim was to delineate novel EDEM2 substrate candidates using a two-step strategy. The first one refers to the deglycoproteomics dataset, which covers nanoLC-MS/MS analysis of Concanavalin A enriched glycopeptides released by endoglycosidase digestion from A375 melanoma cell lysates. This allowed us to map the fraction of glycoproteins with non-matured N-glycans from A375 melanoma cells and find or validate N-glycosylation sites of proteins from the secretory pathway. The same dataset was also used to define glycoproteins altered by the down-regulation of endogenous EDEM2, which should contain its candidate-substrates. In a second step we delineate the degradation kinetics of some of these proteins using a pulse SILAC strategy (pSILAC) thus complementing our initial findings with a fourth dataset. Beside nanoLC-MS/MS analysis our findings were also validated by various biochemical experiments. All the data described are associated with a research article published in Molecular and Cellular Proteomics [1].

Affinity Proteomics and Deglycoproteomics Uncover Novel EDEM2 Endogenous Substrates and an Integrative ERAD Network.

Various pathologies result from disruptions to or stress of endoplasmic reticulum (ER) homeostasis, such as Parkinson's disease and most neurodegenerative illnesses, diabetes, pulmonary fibrosis, viral infections, and cancers. A critical process in maintaining ER homeostasis is the selection of misfolded proteins by the ER quality-control system for destruction via ER-associated degradation (ERAD). One key protein proposed to act during the first steps of misfolded glycoprotein degradation is the ER degradation-enhancing α-mannosidase-like protein 2 (EDEM2). Therefore, characterization of the EDEM2-associated proteome is of great interest. We took advantage of using melanoma cells overexpressing EDEM2 as a cancer model system, to start documenting at the deglycoproteome level (N-glycosites identification) the emerging link between ER homeostasis and cancer progression. The dataset created for identifying the EDEM2 glyco clients carrying high mannose/hybrid N-glycans provides a comprehensive N-glycosite analysis mapping over 1000 N-glycosites on more than 600 melanoma glycoproteins. To identify EDEM2-associated proteins, we used affinity proteomics and proteome-wide analysis of sucrose density fractionation in an integrative workflow. Using intensity and spectral count-based quantification, we identify seven new EDEM2 partners, all of which are involved in ER quality-control system and ERAD. Moreover, we defined novel endogenous candidates for EDEM2-dependent ERAD by combining deglycoproteomics, stable isotope labeling with amino acids in cell culture-based proteomics, and biochemical methods. These included tumor antigens and several ER-transiting endogenous melanoma proteins, including integrin alpha-1 and protocadherin 2, the expression of which was negatively correlated with that of EDEM2. Tumor antigens are key in the antigen presentation process, whereas integrin alpha-1 and protocadherin 2 are involved in melanoma metastasis and invasion. EDEM2 could therefore have a regulatory role in melanoma through the modulation of degradation and trafficking in these glycoproteins. The data presented herein suggest that EDEM2 is involved in ER homeostasis to a greater extent than previously suggested.