title: MHC class II presentation of gp100 epitopes in melanoma cells requires the function of conventional endosomes and is influenced by melanosomes.
abstract: Many human solid tumors express MHC class II (MHC-II) molecules, and proteins normally localized to melanosomes give rise to MHC-II-restricted epitopes in melanoma. However, the pathways by which this response occurs have not been defined. We analyzed the processing of one such epitope, gp100(44-59), derived from gp100/Pmel17. In melanomas that have down-regulated components of the melanosomal pathway, but constitutively express HLA-DR*0401, the majority of gp100 is sorted to LAMP-1(high)/MHC-II(+) late endosomes. Using mutant gp100 molecules with altered intracellular trafficking, we demonstrate that endosomal localization is necessary for gp100(44-59) presentation. By depletion of the AP-2 adaptor protein using small interfering RNA, we demonstrate that gp100 protein internalized from the plasma membrane to such endosomes is a major source for gp100(44-59) epitope production. The gp100 trapped in early endosomes gives rise to epitopes that are indistinguishable from those produced in late endosomes but their production is less sensitive to inhibition of lysosomal proteases. In melanomas containing melanosomes, gp100 is underrepresented in late endosomes, and accumulates in stage II melanosomes devoid of MHC-II molecules. The gp100(44-59) presentation is dramatically reduced, and processing occurs entirely in early endosomes or stage I melanosomes. This occurrence suggests that melanosomes are inefficient Ag-processing compartments. Thus, melanoma de-differentiation may be accompanied by increased presentation of MHC-II restricted epitopes from gp100 and other melanosome-localized proteins, leading to enhanced immune recognition.
authors.affiliation: Department of Microbiology and Carter Immunology Center, University of Virginia School of Medicine, Charlottesville, VA 22908, USA.
authors.forename: Valentina
authors.initials: V
authors.lastname: Robila
authors.forename: Marina
authors.initials: M
authors.lastname: Ostankovitch
authors.forename: Michelle L
authors.initials: ML
authors.lastname: Altrich-Vanlith
authors.forename: Alexander C
authors.initials: AC
authors.lastname: Theos
authors.forename: Sheila
authors.initials: S
authors.lastname: Drover
authors.forename: Michael S
authors.initials: MS
authors.lastname: Marks
authors.forename: Nicholas
authors.initials: N
authors.lastname: Restifo
authors.forename: Victor H
authors.initials: VH
authors.lastname: Engelhard
mesh_terms: D033962:Adaptor Protein Complex 2 / Q000276:immunology; D017951:Antigen Presentation / Q000276:immunology*; D000951:Antigens, Neoplasm / Q000276:immunology*; D015816:Cell Adhesion Molecules, Neuronal / Q000276:immunology; D054337:Cell Dedifferentiation / Q000276:immunology; D045744:Cell Line, Tumor; D011992:Endosomes / Q000276:immunology*; D018984:Epitopes, T-Lymphocyte / Q000276:immunology*; D058851:GPI-Linked Proteins; D006684:HLA-DR Antigens / Q000276:immunology*; D006801:Humans; D008545:Melanoma / Q000276:immunology*; D020460:Melanosomes / Q000276:immunology*; D008562:Membrane Glycoproteins / Q000276:immunology*; D021381:Protein Transport / Q000276:immunology; D034741:RNA, Small Interfering / Q000276:immunology; D058951:gp100 Melanoma Antigen
chemical_list: D033962:Adaptor Protein Complex 2; D000951:Antigens, Neoplasm; D015816:Cell Adhesion Molecules, Neuronal; D018984:Epitopes, T-Lymphocyte; D058851:GPI-Linked Proteins; D006684:HLA-DR Antigens; D008562:Membrane Glycoproteins; C548637:PMEL protein, human; D034741:RNA, Small Interfering; D058951:gp100 Melanoma Antigen; C095362:limbic system-associated membrane protein