title: A protein disulfide isomerase/thioredoxin-1 complex is physically attached to exofacial membrane tumor necrosis factor receptors: overexpression in chronic lymphocytic leukemia cells.
abstract: OBJECTIVE
  The 3D structures and functions of cysteine-rich receptors such as tumor necrosis factor receptors (TNFRs) are redox-modulated by dithiol-disulfide exchange. TNFR superfamily members participate in growth regulation in B-cell chronic lymphocytic leukemia (CLL), and tissue stromal cells interact with leukemia cells, profoundly affecting their viability via release of redox-active components, including cysteine, thioredoxin-1 (Trx1), and Trx reductase. Trx1 was previously shown to enhance release of TNF, which acts as an autocrine/paracrine growth factor in CLL. The nature of the mechanism is not known, however. Here, we investigated whether Trx1 and protein disulfide isomerase (PDI), a chaperone and Trx-family member, may interact with TNFRs.
  
  
  RESULTS
  We found direct physical association between PDI and TNFR1 or TNFR2 by coclustering and affinity isolation. PDI (57 kDa) formed covalent/reduction-sensitive 69-kDa complexes with Trx1 (12 kDa) in a majority of CLL cell samples, detected at low levels only in control B-cells. Functionally, the TNF/TNFR signaling via the nuclear factor kappa B-driven autocrine loop was disrupted in a dose-dependent fashion by PDI-inhibitors bacitracin, anti-PDI, or anti-Trx1 antibodies, resulting in reduced viability. PDI was significantly overexpressed in immunoglobulin heavy-chain variable (IGHV) unmutated versus mutated CLL (p=0.0102), and amplified TNF release was observed in the former group.
  
  
  METHODS
  This study points out a previously unrecognized physical and functional association of TNFRs with the redox-active proteins PDI and Trx1.
  
  
  CONCLUSIONS
  We describe here a new level of TNF regulation, in which membrane TNFRs are redox controlled at the exofacial surface by PDI/Trx1. These findings shed new light on the observed survival benefit in CLL B-cells exerted by TNFR-superfamily ligands and point at potential therapeutic strategies.
authors: Division of Cell Biology, Department of Clinical and Experimental Medicine, Linköping University, Linköping, Sweden.
authors: Anita
authors: A
authors: Söderberg
authors: Akter
authors: A
authors: Hossain
authors: Anders
authors: A
authors: Rosén
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019898:Autocrine Communication; D002462:Cell Membrane / Q000378:metabolism*; D016764:Cell Polarity; D002470:Cell Survival; D002846:Chromatography, Affinity; D005260:Female; D006801:Humans; D015451:Leukemia, Lymphocytic, Chronic, B-Cell; D008297:Male; D008875:Middle Aged; D046912:Multiprotein Complexes / Q000302:isolation & purification / Q000378:metabolism; D010084:Oxidation-Reduction; D011485:Protein Binding; D019704:Protein Disulfide-Isomerases / Q000302:isolation & purification / Q000378:metabolism*; D021381:Protein Transport; D047888:Receptors, Tumor Necrosis Factor, Type I / Q000378:metabolism*; D047889:Receptors, Tumor Necrosis Factor, Type II / Q000378:metabolism*; D015398:Signal Transduction; D059010:Single-Cell Analysis; D013879:Thioredoxins / Q000302:isolation & purification / Q000378:metabolism* / Q000502:physiology; D014407:Tumor Cells, Cultured; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism
chemical_list: D046912:Multiprotein Complexes; D047888:Receptors, Tumor Necrosis Factor, Type I; D047889:Receptors, Tumor Necrosis Factor, Type II; C491203:TXN protein, human; D014409:Tumor Necrosis Factor-alpha; D013879:Thioredoxins; D019704:Protein Disulfide-Isomerases