Melanoma cells present high levels of HLA‐A2‐tyrosinase in association with instability and aberrant intracellular processing of tyrosinase

Abstract

Short-lived protein translation products are proposed to be a major source of substrates for major histocompatibility complex (MHC) class I antigen processing and presentation; however, a direct link between protein stability and the presentation level of MHC class I-peptide complexes has not been made. We have recently discovered that the peptide Tyr (369-377) , derived from the tyrosinase protein is highly presented by HLA-A2 on the surface of melanoma cells. To examine the molecular mechanisms responsible for this presentation, we compared characteristics of tyrosinase in melanoma cells lines that present high or low levels of HLA-A2-Tyr (369-377) complexes. We found no correlation between mRNA levels and the levels of HLA-A2-Tyr (369-377) presentation. Co-localization experiments revealed that, in cell lines presenting low levels of HLA-A2-Tyr (369-377) complexes, tyrosinase co-localizes with LAMP-1, a melanosome marker, whereas in cell lines presenting high HLA-A2-Tyr (369-377) levels, tyrosinase localizes to the endoplasmic reticulum. We also observed differences in tyrosinase molecular weight and glycosylation composition as well as major differences in protein stability (t 1/2 ). By stabilizing the tyrosinase protein, we observed a dramatic decrease in HLA-A2-tyrosinase presentation. Our findings suggest that aberrant processing and instability of tyrosinase are responsible for the high presentation of HLA-A2-Tyr (369-377) complexes and thus shed new light on the relationship between intracellular processing, stability of proteins, and MHC-restricted peptide presentation.Keywords: Class I MHC processing and presentation r TCR-like antibody r Tumor antigens r Tumor immunology r Tyrosinase IntroductionThe source of major histocompatibility complex (MHC) class I peptides has been extensively investigated. The major source of MHC class I peptides are proteins that are never folded correctly due to errors in transcriptional, translational, or posttranslational processes and as such include defective ribosome products (DRiPs) [1]. The MHC class I Ag processing pathway mainly samples newly synthesized proteins as adding Correspondence: Dr. Yoram Reiter e-mail: reiter@tx.technion.ac.il protein synthesis inhibitor to cells almost abolishes the binding of peptides to the transporter associated with antigen presentation (TAP) [2]. Sampling newly synthesized proteins is important for rapid presentation to the immune system that may be critical when cells are infected with a virus; indeed, even though most viral proteins are very stable, presentation of viral-derived peptides on MHC class I molecules and lysis of viral-infected cells is observed within approximately 1 h postinfection [3,4].Proteasomes create antigenic peptides from distinct proteins at different efficiencies: rapidly degraded newly synthesized proteins which represent the DRiPs, the major substrate for MHC class I peptide presentation, which are typically degraded within 10 min of synthesis, and a slower degraded pool of proteins thatwww.eji-journal....

Epitope located N‐glycans impair the MHC‐I epitope generation and presentation

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