title: Ligand of Numb proteins LNX1p80 and LNX2 interact with the human glycoprotein CD8α and promote its ubiquitylation and endocytosis.
abstract: E3 ubiquitin ligases give specificity to the ubiquitylation process by selectively binding substrates. Recently, their function has emerged as a crucial modulator of T-cell tolerance and immunity. However, substrates, partners and mechanism of action for most E3 ligases remain largely unknown. In this study, we identified the human T-cell co-receptor CD8 α-chain as binding partner of the ligand of Numb proteins X1 (LNX1p80 isoform) and X2 (LNX2). Both LNX mRNAs were found expressed in T cells purified from human blood, and both proteins interacted with CD8α in human HPB-ALL T cells. By using an in vitro assay and a heterologous expression system we showed that the interaction is mediated by the PDZ (PSD95-DlgA-ZO-1) domains of LNX proteins and the cytosolic C-terminal valine motif of CD8α. Moreover, CD8α redistributed LNX1 or LNX2 from the cytosol to the plasma membrane, whereas, remarkably, LNX1 or LNX2 promoted CD8α ubiquitylation, downregulation from the plasma membrane, transport to the lysosomes, and degradation. Our findings highlight the function of LNX proteins as E3 ligases and suggest a mechanism of regulation for CD8α localization at the plasma membrane by ubiquitylation and endocytosis.
authors: Dipartimento di Biochimica e Biotecnologie Mediche, University of Naples Federico II, Via S. Pansini 5, 80131 Naples, Italy.
authors: Massimo
authors: M
authors: D'Agostino
authors: Giusy
authors: G
authors: Tornillo
authors: Maria Gabriella
authors: MG
authors: Caporaso
authors: Maria Vittoria
authors: MV
authors: Barone
authors: Eric
authors: E
authors: Ghigo
authors: Stefano
authors: S
authors: Bonatti
authors: Giovanna
authors: G
authors: Mottola
mesh_terms: D016827:CD8 Antigens / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D002462:Cell Membrane / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D004705:Endocytosis; D006801:Humans; D054731:PDZ Domains; D011485:Protein Binding; D044767:Ubiquitin-Protein Ligases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D054875:Ubiquitination
chemical_list: D016827:CD8 Antigens; D002352:Carrier Proteins; D044767:Ubiquitin-Protein Ligases; C409469:CD8 antigen, alpha chain; C570847:LNX2 protein, human; C484733:LNX1 protein, human