Inhibition of MHC Class II Expression and Immune Responses by c-MIR

Abstract

We previously reported a novel E3 ubiquitin ligase (E3), designated as c-MIR, which targets B7-2 to lysosomal degradation and down-regulates the B7-2 surface expression through ubiquitination of its cytoplasmic tail. B7-2 is well known as a costimulatory molecule for Ag presentation, suggesting that the manipulation of c-MIR expression modulates immune responses in vivo. To examine this hypothesis, we generated genetically modified mice in which c-MIR was expressed under an invariant chain (Ii) promoter. Dendritic cells derived from genetically engineered mice showed low ability to present Ags. In addition, these mice showed resistance to the onset of experimental autoimmune encephalomyelitis and an impaired development of CD4 T cells in the thymus and the periphery. These findings led us to conclude that MHC class II (MHC II) is an additional target for c-MIR. Indeed, forced expression of c-MIR in several B cell lines down-regulated the surface expression of MHC II, and down-regulation was found to depend on the presence of a single lysine residue in the cytoplasmic tail of the I-A β-chain. In a reconstitution system using 293T cells, we found that the lysine residue at position 225 in the I-A β-chain was ubiquitinated by c-MIR. To our knowledge, c-MIR is the first example of an E3 that is capable of inhibiting MHC II expression. Our findings suggest that c-MIR might potently regulate immune responses in vivo.

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

“…2A Upper). Surface HLA-DR levels were affected by the overexpression of MARCH I-eGFP and also, as expected, by MARCH VIII-eGFP (10). We thereby tested whether a single lysine residue in the cytoplasmic tail of the MHC-II ␤-chain was required by MARCH I to induce HLA-DR surface downregulation.…”

“…MARCH proteins are E3 ubiquitin ligases that have been reported to down-regulate several surface molecules including transferrin receptor (TfR), MHC class I and II, and CD86 (7,10). We evaluated the capacity of different human MARCH ligases to control HLA-DR surface expression through transfection of class II transactivator (CIITA)-expressing HeLa cells (14).…”

“…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)(7)(8)(9)(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).…”

“…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)(7)(8)(9)(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).…”

Dendritic cell preactivation impairs MHC class II presentation of vaccines and endogenous viral antigens

“…Mature DCs down-regulate macropinocytosis and phagocytosis, although they retain their micropinocytic activity (3,4). Mature DCs accumulate long-lived surface MHC II-peptide complexes, derived from antigens contained within the endosomal compartments at the time of activation (5)(6)(7)(8)(9)(10)55). Such antigens correspond to proteins captured from the extracellular medium (exogenous), or those synthesized by the DCs themselves (endogenous).…”