title: Expression of LA45 reactive beta 2-microglobulin free HLA class I alpha-chains on activated T-cells is regulated by internalization, constitutive and protein kinase C inducible release.
abstract: HLA Class I molecules on activated T cells are expressed as mAb W6/32 reactive heterodimers associated with beta 2-microglobulin (beta 2-m) and also as mAb LA45 reactive beta 2-m free HLA Class I alpha-chains. However, the regulation of free alpha-chain expression remained enigmatic. Here we show, that the amount of cell surface expressed free heavy chains is influenced by two distinct mechanisms. Firstly, a proportion of expressed molecules are cleaved and give rise to a soluble pool of HLA Class I molecules. We provide evidence that, besides the previously described constitutive release of free alpha chains, a second phorbol ester inducible release mechanism involving activation of protein kinase C (PKC) does exist. We demonstrate that both the constitutive and the enhanced release of LA45 reactive HLA Class I alpha-chains are the consequence of a cell membrane bound proteolytic activity with the characteristics of a 1, 10 phenanthroline sensitive metalloprotease. Secondly, we report that a distinct fraction of mAb tagged free alpha-chains is internalized via an n-ethylmaleimide sensitive pathway. Together, this data suggests that the expression of free alpha-chains is regulated by pathways governing release and internalization.
authors.affiliation: Institute for Immunology, University of Vienna, Austria.
authors.forename: W F
authors.initials: WF
authors.lastname: Pickl
authors.forename: W
authors.initials: W
authors.lastname: Holter
authors.forename: J
authors.initials: J
authors.lastname: Stöckl
authors.forename: O
authors.initials: O
authors.lastname: Majdic
authors.forename: W
authors.initials: W
authors.lastname: Knapp
mesh_terms: D000911:Antibodies, Monoclonal; D002460:Cell Line; D015536:Down-Regulation / Q000187:drug effects; D004492:Edetic Acid / Q000494:pharmacology; D005033:Ethylmaleimide / Q000494:pharmacology; D019084:Fluorescent Antibody Technique, Indirect; D015395:Histocompatibility Antigens Class I / Q000096:biosynthesis* / Q000187:drug effects; D006801:Humans; D008666:Metalloendopeptidases / Q000187:drug effects / Q000502:physiology; D010618:Phenanthrolines / Q000494:pharmacology; D010703:Phorbol Esters / Q000494:pharmacology; D011480:Protease Inhibitors / Q000494:pharmacology; D011493:Protein Kinase C / Q000187:drug effects / Q000378:metabolism; D019311:Staurosporine / Q000494:pharmacology; D013601:T-Lymphocytes / Q000378:metabolism*
chemical_list: D000911:Antibodies, Monoclonal; D015395:Histocompatibility Antigens Class I; C063959:LA45 antigen; D010618:Phenanthrolines; D010703:Phorbol Esters; D011480:Protease Inhibitors; D004492:Edetic Acid; D011493:Protein Kinase C; D008666:Metalloendopeptidases; D019311:Staurosporine; D005033:Ethylmaleimide; C025205:1,10-phenanthroline