Caspases and nitric oxide broadly regulate dendritic cell maturation and surface expression of class II MHC proteins

Abstract

The passage of dendritic cells (DC) from immature to terminally differentiated antigen-presenting cells is accompanied by numerous morphological, phenotypic, and functional changes. These changes include, for example, expression of ''empty'' class II MHC proteins (MHCII) at the surface in immature DC, whereas a much larger amount of peptide-loaded MHCII is expressed at the surface in mature DC. Here we show that, in cultured immature DC derived from murine bone-marrow precursors, a number of molecules involved in intracellular trafficking were present in a cleaved form, degraded by caspase-like proteases. Cleavage was either inhibited or reduced significantly during maturation of DC induced by either LPS and TNF-␣ or by peptides that inhibit caspase activities. Inducible nitric oxide (NO) synthetase up-regulated by LPS was essential for inhibiting the caspase-like activity during the maturation of DC. Moreover, treatment with LPS or caspase inhibitor resulted in expression of MHCII͞peptide complexes at the cell surface. Thus, the alteration of the endosomal trafficking pathways during the development of DC that parallels the changes in surface expression of MHCII is regulated at least in part by the activities of caspases, inducible NO synthetase, and its product NO.antigen presentation ͉ endosomes ͉ LPS ͉ nitric oxide synthetase ͉ protease inhibitors

Apoptosis‐induced inhibition of CD1d‐mediated antigen presentation: different roles for caspases and signal transduction pathways

“…Caspases have been found to cleave the AP-1 and AP-2 proteins that play an important role in trafficking of MHC class II molecules, which traverse through at least some of the same endocytic compartments as CD1d molecules. 45 Interestingly, and similar to CD1d, we found that camptothecin treatment also inhibits MHC class II-mediated antigen presentation (data not shown). Furthermore, CD1d/LAMP-1 co-localization (%) * *** Figure 6.…”

A novel CARD containing splice-isoform of CIITA regulates nitric oxide synthesis in dendritic cells

“…NO then further inhibits caspases and enhances NOS2 expression and NO synthesis in mature DC. We have shown previously that inhibition of caspases by NO upregulates expression of CD74 (Huang et al, 2008) and other endosomal proteins (Wong et al, 2004;Santambrogio et al, 2005), which is essential for regulating the MHC IIrestricted antigen presentation pathway. This subsequently enhances the capability of DC in inducing T cell proliferation/ activation.…”

“…N9, a wellcharacterized murine microglial cell line was a kind gift from Dr. Ricciardi-Castagnoli. Bone marrow-derived DC from 6-to 7-week-old C57BL/6J mice was established by the bulk-culture method as previously described (Wong et al, 2004). Briefly, bone-marrow cells were harvested from the long bones and plated on dishes in complete DMEM with 10% FCS containing 20 ng/mL of mouse recombinant GM-CSF (R&D Systems, USA).…”

“…To prove this hypothesis, cell extracts from primary DC, which has high caspase activity (Wong et al, 2004), were incubated for 4 h with either GSTor a GST-DC-CASPIC protein, together with caspase-1 substrate (p-YVAD), caspase-3 substrate (p-DEVD) or caspase-8 substrate (p-IETD), respectively. Then caspase activity was analyzed using a fluorescence reader.…”

Forced Expression of HLA-DM at the Surface of Dendritic Cells Increases Loading of Synthetic Peptides on MHC Class II Molecules and Modulates T Cell Responses

“…This minor peptide loading pathway depends on the presence of extracellular proteases capable of processing Ags. In immature DCs, one can speculate that the caspase-mediated inactivation of AP-2, the adaptor protein complex that mediates internalization of proteins with tyrosine-based sorting motifs, causes the accumulation of DM at the plasma membrane (13). On maturation, internalization of DM to endocytic compartments resumes and most MHC II become filled with peptides (11).…”