Transient aggregation of ubiquitinated proteins during dendritic cell maturation

Abstract

Dendritic cells (DCs) are antigen-presenting cells with the unique capacity to initiate primary immune responses. Dendritic cells have a remarkable pattern of differentiation (maturation) that exhibits highly specific mechanisms to control antigen presentation restricted by major histocompatibility complex (MHC). MHC class I molecules present to CD8(+) cytotoxic T cells peptides that are derived mostly from cytosolic proteins, which are ubiquitinated and then degraded by the proteasome. Here we show that on inflammatory stimulation, DCs accumulate newly synthesized ubiquitinated proteins in large cytosolic structures. These structures are similar to, but distinct from, aggresomes and inclusion bodies observed in many amyloid diseases. Notably, these dendritic cell aggresome-like induced structures (DALIS) are transient, require continuous protein synthesis and do not affect the ubiquitin-proteasome pathway. Our observations suggest the existence of an organized prioritization of protein degradation in stimulated DCs, which is probably important for regulating MHC class I presentation during maturation.

Differential use of autophagy by primary dendritic cells specialized in cross-presentation

“…Ubiquitinated protein aggregates are known to be targeted by autophagy 23,24 and are of particular interest given that dendritic cell aggresome-like inducible structures (DALIS) have been previously detected in bone marrow-derived and epidermal sheet DC following activation. 25 DALIS function as a reservoir for MHC I antigens and are putative substrates of autophagy. 26 Here, we detected ubiquitinated aggregates in the primary DC subsets using an antibody that recognizes poly-and mono-ubiquitinated proteins, but not free ubiquitin.…”

The identification of wadB, a new glycosyltransferase gene, confirms the branched structure and the role in virulence of the lipopolysaccharide core of Brucella abortus

“…Coverslips were processed for immunofluorescence staining as previously described [5,20]. BMDCs were labeled using an antibody (rabbit anti mouse Rivoli) against a conserved cytoplasmic domain of MHC-II I-A-β subunits [6,21], followed by the secondary antibody donkey anti-rabbit Cy5. Bacteria were visualized directly since they expressed the green fluorescence protein encoded by the pBBR1MCS-2 GFP plasmid.…”

Dendritic Cell Aggresome-Like-Induced Structure Formation and Delayed Antigen Presentation Coincide in Influenza Virus-Infected Dendritic Cells

“…Recently, it has been reported that during LPS-induced maturation, DCs accumulate newly synthesized ubiquitinated proteins in large cytosolic structures called DALIS (10). It was speculated that these structures play a role in the regulation of MHC class I Ag presentation.…”

“…The detection of several DALIS that are not associated with the nucleus distinguishes them from PODs and the MTOC. DALIS are Triton X-100 resistant and appear in the detergentinsoluble fraction (10). Therefore, we infected BMDCs again with influenza virus at different time points, followed by Triton X-100 extraction, SDS-PAGE, and FK2 Western blot.…”

“…Recently, a new feature of DCs was discovered that could represent a mechanism to enable coordinated maturation and Ag presentation in this cell type. After LPS-induced maturation, DCs transiently accumulate newly synthesized ubiquitinated proteins in an aggregated form in the cytosol (10,11). These protein aggregates are called DC aggresome-like-induced structures (DALIS) because they were observed initially in DCs and resemble aggresomes.…”