These two isoforms selleck screening library are related closely in structure, but functionally distinct. In the present study we used a specific blocking antibody to FcγRIIB. Moreover, in the present study a different dose of GXM (100 µg/ml versus 50 µg/ml),
different types of cells (MonoMac6 cell line versus monocyte-derived macrophages) and different incubation times (2 h versus 2 days) were used. Our previous observations indicated that active SHIP, in cells treated with GXM, was responsible for reduction of NFκB transcriptional activation and negative regulation of inflammatory cytokines. This effect was mediated via GXM/FcγRIIB interaction . The role of SHIP in FasL up-regulation and in GXM-induced apoptosis remains obscure, but we can assume that in our system SHIP activation induced by FcγRIIB engagement plays a direct role in apoptosis induction. Consistent with this hypothesis, early studies buy Cisplatin have shown a pro-apoptotic role of SHIP1 in several cell types, including B cells, myeloid and erythroid cells [44–46]. Moreover, Liu et al. have
reported that myeloid cells from SHIP−/− mice are less susceptible to programmed cell death induced by various apoptotic stimuli via Akt activation . In addition, a substantial amount of literature provides evidence that SHIP1 is required to inhibit Akt activation [45,47–49]. This inhibition is critical for the activation of JNK . Akt negatively regulates apoptosis signal-regulating kinase 1 (ASK1), which activates JNK and p38 transcriptional events , therefore inhibition of Akt could lead to ASK activation with consequent phosphorylation of downstream signalling molecules such as JNK and p38. In this study we demonstrated that GXM induces up-regulation of FasL expression by JNK or p38 signalling, which activate c-Jun independently of each other. In particular, much JNK activation seems to be a consequence of GXM interaction with FcγRIIB, whereas p38 activation is also triggered by the binding of GXM with different
pattern recognition receptors (PRRs). However, the capacity of GXM to engage multiple PRRs, such as TLR-4 and FcgRIIB, which simultaneously transmit activating and inhibitory signals, might justify the high level of complexity of these signalling networks. Indeed, more studies are necessary to unravel the complexity of the GXM-induced signalling pathways. A schematic representation of the proposed pathway is shown in Fig. 8. Collectively, our results highlight a fast track to FasL up-regulation via FcγRIIB, and provide evidence for a mechanism involved in the activation of JNK, p38 and c-Jun. Moreover, the present study amplifies the spectrum of FcγRIIB-mediated effects, indicating that this receptor plays a critical role in transducing multiple signallings which contribute to inducing suppressive effects on innate and adaptive immunity.