The Role of the E3 Ligase Cbl-B in Murine Dendritic Cells

Abstract

Dendritic cells (DCs) are potent antigen-presenting cells with a promising potential in cancer immunotherapy. Cbl proteins are E3 ubiquitin ligases and have been implicated in regulating the functional activity of various immune cells. As an example, c-Cbl negatively affects DC activation. We here describe that another member of the Cbl-protein family (i.e. Cbl-b) is highly expressed in murine bone-marrow-derived DCs (BMDCs). Differentiation of cblb−/− bone marrow mononuclear cells into classical BMDCs is unaltered, except enhanced induction of DEC-205 (CD205) expression. When tested in mixed-lymphocyte reaction (MLR), cblb−/− BMDCs exhibit increased allo-stimulatory capacity in vitro. BMDCs were next in vitro stimulated by various toll like receptor (TLR)-agonists (LPS, Poly(I:C), CpG) and exposed to FITC-labeled dextran. Upon TLR-stimulation, cblb−/− BMDCs produce higher levels of proinflammatory cytokines (IL-1α, IL-6 and TNF-α) and exhibit a slightly higher level of FITC-dextran uptake. To further characterize the functional significance of cblb−/− BMDCs we tested them in antigen-specific T cell responses against ovalbumin (OVA) protein and peptides, activating either CD8+ OT-I or CD4+ OT-II transgenic T cells. However, cblb−/− BMDCs are equally effective in inducing antigen-specific T cell responses when compared to wildtype BMDCs both in vitro and in vivo. The migratory capacity into lymph nodes during inflammation was similarly not affected by the absence of Cbl-b. In line with these observations, cblb−/− peptide-pulsed BMDCs are equally effective vaccines against OVA-expressing B16 tumors in vivo when compared to wildtype BMDCs. We conclude that in contrast to c-Cbl, Cbl-b plays only a limited role in the induction of Ag-specific T cell responses by murine BMDCs in vitro and in vivo.

Ascophyllan Purified from Ascophyllum nodosum Induces Th1 and Tc1 Immune Responses by Promoting Dendritic Cell Maturation

“…Recently, studies have shown that various types of polysaccharides can activate DCs by combining with the TLRs [27,28,29]. Moreover, many lines of research showed that MyD88 signaling pathway is essential for DC maturation mediated by TLR ligands [27,30,31].…”

E3 ubiquitin ligase Cbl-b negatively regulates C-type lectin receptor–mediated antifungal innate immunity

“…Subsequently, Cbl-b was shown to target MyD88 and TRIF (Toll/IL-1 receptor domain–containing adapter inducing IFN-β; Han et al, 2010 ), which is potentiated by activating the tyrosine kinases Src and Syk in macrophages upon TLR stimulation. Furthermore, a recent study showed that Cbl-b–deficient BMDCs upon TLR stimulation can produce higher levels of proinflammatory cytokines including IL-1α, IL-6, and TNF and exhibit a slightly higher level of FITC-dextran uptake ( Wallner et al, 2013 ). It has been reported that Cbl-b targets CARMA1, a critical signaling molecule for NF-κB activation, for monoubiquitination in NKT cells ( Kojo et al, 2009 ) and regulates NK cell functions via TAM receptors ( Paolino et al, 2014 ).…”

The E3 Ubiquitin Ligase c‐Cbl Inhibits Microglia‐Mediated CNS Inflammation by Regulating PI3K/Akt/NF‐κB Pathway

“…So, inhibiting microglial activation is thought to be a promising therapeutic strategy in the treatment of chronic neurodegeneration [7]. Cbl proteins are E3 ubiquitin ligases and have been implicated in regulating the functional activity of various immune cells [26][27][28][29]. Previous study showed that Cbl-b is necessary to prevent the inappropriate activation of NF-jB in response to LPS and polymicrobial sepsis [30].…”

“…Cbl proteins are E3 ubiquitin ligases and have been implicated in regulating the functional activity of various immune cells . Previous study showed that Cbl‐b is necessary to prevent the inappropriate activation of NF‐ κ B in response to LPS and polymicrobial sepsis .…”