MHC class II stabilization at the surface of human dendritic cells is the result of maturation-dependent MARCH I down-regulation

Abstract

In response to Toll-like receptor ligands, dendritic cells (DCs) dramatically enhance their antigen presentation capacity by stabilizing at the cell-surface MHC II molecules. We demonstrate here that, in human monocyte-derived DCs, the RING-CH ubiquitin E3 ligase, membrane-associated RING-CH I (MARCH I), promotes the ubiquitination of the HLA-DR ␤-chain. Thus, in nonactivated DCs, MARCH I induces the surface internalization of mature HLA-DR complexes, therefore reducing their stability and levels. We further demonstrate that the maturation-dependent down-regulation of MARCH I is a key event in MHC class II up-regulation at the surface of LPS-activated DCs. MARCH I is, therefore, a major regulator of HLA-DR traffic, and its loss contributes to the acquisition of the potent immunostimulatory properties of mature human DCs.antigen presentation ͉ ubiquitin ligase ͉ endocytosis ͉ LPS ͉ TLR A ctivation of dendritic cells (DCs) by invading pathogens involves a process of maturation that converts an immature DC (iDC) to a mature DC (mDC) and a subsequent Toll-like receptor (TLR)-mediated immune response. This process is accompanied by a marked cellular reorganization (1, 2). Redistribution of MHC class II molecules (MHC class II) from late endosomal compartments to the plasma membrane (3) represents one of the major functional events observed during the acquisition of the immunostimulatory function by mDCs. Recently in mouse DCs, ubiquitination of lysine-225 in the cytoplasmic tail of MHC II ␤-chain has been shown to be determinant for the targeting and accumulation of the mature form of MHC II in the lysosomes of iDCs (4, 5). Interestingly, ubiquitination of MHC II in murine DCs ceases on maturation, thus contributing to the increased level of MHC II at the cell surface (4, 5). Membrane-associated RING-CH (MARCH) proteins represent a family of E3 ubiquitin ligases, which all contain a variant catalytical RING-finger domain (RING-CH domain, C4HC3) located at the N terminus (6-10). It has been recently reported that transgenic overexpression of MARCH VIII/c-MIR in mouse splenic antigen-presenting cells (APCs) leads to internalization of surface CD86/B7-2 and MHC II, and subsequent lysosomal degradation (10). Furthermore, deletion of MARCH I, another E3 ubiquitin ligase, promoted an increase of surface MHC II levels in mouse B cells, although a direct implication of this ligase in the process of MHC II internalization was excluded (11). We identify here human MARCH I as a potent regulator of HLA-DR surface expression and explore its role during human monocyte-derived DC (MoDC) activation. We further show that MARCH I expression is lost at late stages of DC maturation and thereby participates in the stabilization of peptideloaded HLA-DR at the cell surface. Our observations suggest that MARCH I is essential to coordinate MHC II-restricted antigen presentation during human DC activation by TLR ligands. Results MHC Class II Ubiquitination Is Regulated in MoDCs.The subcellular localization of MHC class II (HLA-DR) in CD14 ϩ M...

Tolerogenicity is not an absolute property of a dendritic cell

“…Transcription of MARCH1 and MARCH8 was, however, essentially unchanged in all of the populations (B6 data not shown). This contrasts with previous studies using human monocyte-derived DC where downregulation of MARCH1 followed maturation, and a pronounced increase in MARCH1 was seen in response to IL-10 [22,23].…”

“…The E3 ubiquitin ligases MARCH1 and MARCH8 are known to be involved in regulating MHC class II and CD86, with maturationinduced loss of ubiquitination promoting cell surface expression [19][20][21]. Pronounced changes previously reported in the level of MARCH1 mRNA in human monocyte-derived DC, 20-fold on maturation and 40-fold in response to IL-10 [22,23], were not evident in our data (Supporting Information Fig. 2A).…”

MHC Class II Antigen Presentation by Dendritic Cells Regulated through Endosomal Sorting

“…Activation of conventional DCs (cDCs) strongly reduces ubiquitination of MHCII, intervening with its targeting to ILVs (Shin et al 2006;van Niel et al 2006;De Gassart et al 2008;Walseng et al 2010b). Reduction in ILV targeting leads to rerouting of pMHCII to the cell surface, possibly by default (see above), therewith elevating expression levels at the plasma membrane.…”

“…Ubiquitination of MHCII is largely driven by MARCH1 (Matsuki et al 2007;De Gassart et al 2008), a member of the family of MARCH E3 ligases (Nathan and Lehner 2009). Besides MHCII, the costimulatory molecule CD86 is also targeted by MARCH1-driven ubiquitination to lysosomes (Baravalle et al 2011).…”

Autoregulation of MARCH1 Expression by Dimerization and Autoubiquitination

“…Although MARCH8 appears to be expressed in many different cell types, MARCH1 is mainly found in secondary lymphoid organs, more specifically in the endocytic pathway of dendritic cells (DCs) and B cells (11)(12)(13)(14)(15). MARCH1 reduces the half-life of peptide/MHC II complexes by causing their redistribution from recycling endosomes to lysosomes (12,16).…”