Dataset Information

The effect of proteasome inhibition on the HLA peptidome

ABSTRACT: The Major histocompatibility complex (MHC) class I peptidome is thought to be generated mostly through proteasomal degradation of cellular proteins, a notion that is based on the alterations in presentation of selected peptides following proteasome inhibition. We evaluated the effects of proteasome inhibitors, epoxomicin and bortezomib, on human cultured cancer cells. Since the inhibitors did not reduce the level of presentation of the cell surface human leukocyte antigen (HLA) molecules, we followed their effects on the rates of synthesis of both HLA peptidome and proteome of the cells, using dynamic stable isotope labeling in tissue culture (dynamic-SILAC). The inhibitors reduced the rates of synthesis of most cellular proteins and HLA peptides, yet the synthesis rates of some of the proteins and HLA peptides was not decreased by the inhibitors and of some even increased. Therefore, we concluded that the inhibitors affected the production of the HLA peptidome in a complex manner, including modulation of the synthesis rates of the source proteins of the HLA peptides in addition to their effect on their degradation. The collected data may suggest that the current reliance on proteasome inhibition may overestimate the centrality of the proteasome in the generation of the MHC peptidome. It is therefore suggested that the relative contribution of the proteasomal and non-proteasomal pathways to the production of the MHC peptidome should be revaluated in accordance with the inhibitors effects on the synthesis rates of the source proteins of the MHC peptides. Bioinformatics & data processing: Peptides were identified and the dynamic-SILAC data were quantified using the MaxQuant and the Proteome Discoverer software tools. Graphical representation of the bioinformatics results was performed with Perseus, version 1.3.0.4. MaxQuant [54] version 1.3.0.5 was used with the Andromeda search engine [55] and the human section of Nov 2011 of UniProt containing 20257 entries and mass tolerance of 6 ppm for the precursor masses and 0.5 Da for the fragments. Methionine oxidation was accepted as variable modification for both tryptic and HLA peptides. Carbamidomethyl cysteine and n-acetylation were accepted as modification for the proteomics analyses. Minimal peptide length was set to 7 amino acids and a maximum of two missed cleavages was allowed for tryptic peptides. The false discovery rate (FDR) was set for tryptic peptides to 0.01 for protein identifications, and 0.05 for the MHC peptides. The resulting identified protein tables were filtered to eliminate the identifications derived from the reverse database, as well as common contaminants. Proteome Discoverer version 1.3 (Thermo-Fisher) was used with UniProt of April 2012 for the Sequest search (containing 20220 entries) and July 2012 for the Mascot search (containing 20306 entries). Masses tolerance was set to 6 ppm for the precursors and 0.5 Da for the fragments. Methionine oxidation and n-acetylation were accepted as variable modification for both tryptic and HLA peptides. Carbamidomethyl cysteine was set as fixed modification for the proteomics analyses. Mass range of 350-5000 Da was used for tryptic peptides and mass range of 750-2500 Da was used for the MHC peptides. For both tryptic and MHC peptides the PSMs were filtered with at least 0.05 FDR (medium confidence), peptide maximum rank was set to 1. Minimal number of identified peptides per proteins was set to 2.

INSTRUMENT(S): LTQ Orbitrap

ORGANISM(S): Homo Sapiens (human)

SUBMITTER: Arie Admon

LAB HEAD: Arie Admon

PROVIDER: PXD000171 | Pride | 2018-11-27

REPOSITORIES: Pride

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The effect of proteasome inhibition on the generation of the human leukocyte antigen (HLA) peptidome.

Milner Elena E Gutter-Kapon Lilach L Bassani-Strenberg Michal M Barnea Eilon E Beer Ilan I Admon Arie A

Molecular & cellular proteomics : MCP 20130328 7

The Major histocompatibility complex (MHC) class I peptidome is thought to be generated mostly through proteasomal degradation of cellular proteins, a notion that is based on the alterations in presentation of selected peptides following proteasome inhibition. We evaluated the effects of proteasome inhibitors, epoxomicin and bortezomib, on human cultured cancer cells. Because the inhibitors did not reduce the level of presentation of the cell surface human leukocyte antigen (HLA) molecules, we f ...[more]

PMID: 23538226

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Project description:Human leukocyte antigen (HLA) - B*51:01 and endoplasmic reticulum aminopeptidase 1 (ERAP1) are two strong predisposing genetic factors to Behçet's disease (BD). Previous studies have focused on two subgroups of HLA-B*51 peptidome containing Proline (Pro) or Alanine (Ala) at position 2 (P2). Little is known about the unconventional non-Pro/Ala2 HLA-B*51-bound peptides. We aimed to study the features of this novel sub-peptidome, and investigate its regulation by ERAP1. CRISPR-Cas9 was used to generate an HLA-ABC-knockout HeLa cell line (HeLa.ABC-KO), which was subsequently transduced to express HLA-B*51:01 (HeLa.ABC-KO.B51). ERAP1 was silenced using lentiviral shRNA. Peptides bound to HLA-B*51:01 were eluted and analyzed by Mass Spectrometry. The characteristics of non-Pro/Ala2, Pro2 and Ala2 peptides, and their alteration by ERAP1 silencing were investigated. Effects of ERAP1 silencing on cell surface expression of HLA-B*51:01 were studied using flow cytometry. More than 20% of peptides eluted from HLA-B*51:01 lacked Proline or Alanine at P2. This unconventional group of HLA-B*51:01-bound peptides was enriched for 8-mers (with fewer 9-mers) compared to Pro2 and Ala2 sub-peptidomes, and had similar N-terminal and C-terminal residue usages to Ala2 peptides with the exception of the less abundant Leucine at position Ω. Knockdown of ERAP1 increased the percentage of non-Pro/Ala2 to approximately 40%, increased the percentage of longer (10-mer and 11-mer) peptides eluted from HLA-B*51:01 complexes, and abrogated the predominance of Leucine at P1. Interestingly knockdown of ERAP1 altered the length and N-terminal residue usage of non-Ala2&Pro2 and Ala2 but not the Pro2 peptides. Finally, ERAP1 silencing regulated the expression levels of cell surface HLA-B*51 in a cell type - dependent manner. The HLA-B*51:01 peptidome includes a surprisingly high proportion of unconventional non-Pro/Ala2 peptides which are increased by ERAP1 silencing, mimicking the loss-of-function BD risk variant.

Project description:Treatment of cancer cells with anti-cancer drugs often fails to achieve complete remission. Yet, such drug treatments may induce alteration in the tumorâs gene expression patterns, including those of Cancer/Testis Antigens (CTA). The degradation products of such antigens can be presented as HLA peptides on the surface of the tumor cells and be developed into anti-cancer immunotherapeutics. For example, the DNA methyl transferase inhibitor, 5-aza-2'-deoxycytidine (Decitabine) has limited anti-tumor efficacy, yet it induces the expression of many genes, including CTAs that are normally silenced in the healthy adult tissues. In this study, the presentation of many new HLA peptides derived from CTAs and induced by Decitabine was demonstrated in three human Glioblastoma cell lines. Such presentation of CTA-derived HLA peptides can be exploited for development of new treatment modalities, combining drug treatment with anti-CTA targeted immunotherapy. The Decitabine-induced HLA peptidomes include many CTAs that are not normally detected in healthy tissues or in cancer cells, unless treated with the drug. In addition, the study included large-scale analyses of the simultaneous effects of Decitabine on the transcriptomes, proteomes and HLA peptidomes of the human Glioblastoma cells. It demonstrates the poor correlations between these three levels of gene expression, both in their total levels and in their response to the drug. The transcriptomes, proteomes and HLA peptidomes of the U-87, T98G and LNT-229 GBM human cell lines were analyzed before and after treatment with Decitabine. Overall, the RNA-Seq transcriptome analyses resulted in the identification of above 26000 transcripts, the proteome analyses identified about 7500 proteins and the HLA class I peptidome analyses resulted in above 25000 identified HLA peptides. Two biological repetitions of the transcriptome, three of the proteome and three of the HLA peptidome were performed with each of the cell lines and treatment, resulting in highly reproducible datasets.

Project description:Background: Patient derived organoids (PDOs) can be established from colorectal cancers as in vitro models to interrogate cancer biology and its clinical relevance. We applied mass spectrometry (MS) immunopeptidomics to investigate neoantigen presentation and whether this can be augmented through interferon gamma (IFN) or MEK-inhibitors. Methods: Four PDOs from chemotherapy refractory and one from a treatment naïve CRC were expanded to replicates with 100 million cells each, and HLA class I and class II peptide ligands were analysed by MS. Results: We identified an average of 9,936 unique peptides per PDO which compares favourably against published immunopeptidomics studies, suggesting high sensitivity. Loss of heterozygosity of the HLA locus was associated with low peptide diversity in one PDO. Peptides from genes without detectable expression by RNA-sequencing were rarely identified by MS. Only 3 out of 612 non-silent mutations encoded for neoantigens that were detected by MS. Treatment of four PDOs with IFN upregulated HLA class I expression and qualitatively changed the immunopeptidome, with increased presentation of IFN-inducible genes. HLA class II presented peptides increased on average 16-fold with IFN treatment. MEK-inhibitor treatment showed no consistent effect on class I or II HLA expression or the peptidome. Importantly, no additional HLA class I or II presented neoantigens became detectable with any treatment. Conclusions: Only 3 out of 612 non-synonymous mutations encoded for neoantigens that were detectable by MS. Although MS has sensitivity limits and biases, and likely underestimated the true neoantigen burden, this established a lower bound of the percentage of non-silent mutations that encode for presented neoantigens, which may be as low as 0.5%. This could be a reason for the poor responses of non-hypermutated CRCs to immune checkpoint inhibitors. MEK-inhibitors recently failed to improve checkpoint-inhibitor efficacy in CRC and the observed lack of HLA upregulation or improved peptide presentation may explain this.

Dataset Information

The effect of proteasome inhibition on the HLA peptidome

Publications

The effect of proteasome inhibition on the generation of the human leukocyte antigen (HLA) peptidome.

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