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.
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ABSTRACT: Prostate cancer cell lines have been used in the search for biomarkers that are suitable for prostate cancer diagnosis. Unfortunately, many cell line studies have only involved single cell lines, partially characterized cell lines or were performed without controls, and this may have been detrimental to effective biomarker discovery. We have analyzed a panel of prostate cancer and nonmalignant control cell lines using current biomarkers and then investigated a set of prospective endosomal and lysosomal proteins to search for new biomarkers. Western blotting was used to define the amount of protein and specific molecular forms in cell extracts and culture media from a panel of nonmalignant (RWPE-1, PNT1a, PNT2) and prostate cancer (22RV1, CaHPV10, DU-145, LNCaP) cell lines. Gene expression was determined by qRT-PCR. HPV-18 transfected cell lines displayed a different pattern of protein and gene expression when compared to the other cell lines examined, suggesting that these cell lines may not be the most optimal for prostate cancer biomarker discovery. There was an increased amount of prostatic acid phosphatase and kallikrein proteins in LNCaP cell extracts and culture media, but variable amounts of these proteins in other prostate cancer cell lines. There were minimal differences in the amounts of lysosomal proteins detected in prostate cancer cells and culture media, but two endosomal proteins, cathepsin B and acid ceramidase, had increased gene and protein expression, and certain molecular forms showed increased secretion from prostate cancer cells (P ≤ 0.05). LIMP-2 gene and protein expression was significantly increased in prostate cancer compared to nonmalignant cell lines (P ≤ 0.05). While the existing prostate cancer biomarkers and lysosomal proteins investigated here were not able to specifically differentiate between a panel of nonmalignant and prostate cancer cell lines, endosomal proteins showed some discriminatory capacity. LIMP-2 is a critical regulator of endosome biogenesis and the increased expression observed in prostate cancer cells indicated that other endosome related proteins may also be upregulated and could be investigated as novel biomarkers. Prostate © 2014 Wiley Periodicals, Inc.The Prostate 01/2014; · 3.84 Impact Factor