title: Promiscuous binding of invariant chain-derived CLIP peptide to distinct HLA-I molecules revealed in leukemic cells.
abstract: Antigen presentation by HLA class I (HLA-I) and HLA class II (HLA-II) complexes is achieved by proteins that are specific for their respective processing pathway. The invariant chain (Ii)-derived peptide CLIP is required for HLA-II-mediated antigen presentation by stabilizing HLA-II molecules before antigen loading through transient and promiscuous binding to different HLA-II peptide grooves. Here, we demonstrate alternative binding of CLIP to surface HLA-I molecules on leukemic cells. In HLA-II-negative AML cells, we found plasma membrane display of the CLIP peptide. Silencing Ii in AML cells resulted in reduced HLA-I cell surface display, which indicated a direct role of CLIP in the HLA-I antigen presentation pathway. In HLA-I-specific peptide eluates from B-LCLs, five Ii-derived peptides were identified, of which two were from the CLIP region. In vitro peptide binding assays strikingly revealed that the eluted CLIP peptide RMATPLLMQALPM efficiently bound to four distinct HLA-I supertypes (-A2, -B7, -A3, -B40). Furthermore, shorter length variants of this CLIP peptide also bound to these four supertypes, although in silico algorithms only predicted binding to HLA-A2 or -B7. Immunization of HLA-A2 transgenic mice with these peptides did not induce CTL responses. Together these data show a remarkable promiscuity of CLIP for binding to a wide variety of HLA-I molecules. The found participation of CLIP in the HLA-I antigen presentation pathway could reflect an aberrant mechanism in leukemic cells, but might also lead to elucidation of novel processing pathways or immune escape mechanisms.
authors.affiliation: Department of Hematology, VU Institute for Cancer and Immunology, VU University Medical Center, Amsterdam, The Netherlands. m.luijn@vumc.nl
authors.forename: Marvin M
authors.initials: MM
authors.lastname: van Luijn
authors.forename: Arjan A
authors.initials: AA
authors.lastname: van de Loosdrecht
authors.forename: Margit H
authors.initials: MH
authors.lastname: Lampen
authors.forename: Peter A
authors.initials: PA
authors.lastname: van Veelen
authors.forename: Adri
authors.initials: A
authors.lastname: Zevenbergen
authors.forename: Michel G D
authors.initials: MG
authors.lastname: Kester
authors.forename: Arnoud H
authors.initials: AH
authors.lastname: de Ru
authors.forename: Gert J
authors.initials: GJ
authors.lastname: Ossenkoppele
authors.forename: Thorbald
authors.initials: T
authors.lastname: van Hall
authors.forename: S Marieke
authors.initials: SM
authors.lastname: van Ham
mesh_terms: D000483:Alleles; D000595:Amino Acid Sequence; D000818:Animals; D017951:Antigen Presentation / Q000276:immunology; D000944:Antigens, Differentiation, B-Lymphocyte / Q000737:chemistry / Q000378:metabolism*; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000378:metabolism; D015789:HLA-A2 Antigen / Q000235:genetics / Q000378:metabolism; D015793:HLA-B7 Antigen / Q000235:genetics / Q000378:metabolism; D015395:Histocompatibility Antigens Class I / Q000235:genetics / Q000378:metabolism*; D000949:Histocompatibility Antigens Class II / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D007938:Leukemia / Q000473:pathology*; D051379:Mice; D008822:Mice, Transgenic; D011485:Protein Binding
chemical_list: D000944:Antigens, Differentiation, B-Lymphocyte; D015789:HLA-A2 Antigen; D015793:HLA-B7 Antigen; D015395:Histocompatibility Antigens Class I; D000949:Histocompatibility Antigens Class II; C045084:invariant chain