Constitutive activation of oncogenic PDGFRα-mutant proteins occurring in GIST patients induces receptor mislocalisation and alters PDGFRα signalling characteristics.

BACKGROUND: Gastrointestinal stromal tumours (GIST) are mainly characterised by the presence of activating mutations in either of the two receptor tyrosine kinases c-KIT or platelet-derived growth factor receptor-α (PDGFRα). Most mechanistic studies dealing with GIST mutations have focused on c-KIT and far less is known about the signalling characteristics of the mutated PDGFRα proteins. Here, we study the signalling capacities and corresponding transcriptional responses of the different PDGFRα proteins under comparable genomic conditions. RESULTS: We demonstrate that the constitutive signalling via the oncogenic PDGFRα mutants favours a mislocalisation of the receptors and that this modifies the signalling characteristics of the mutated receptors. We show that signalling via the oncogenic PDGFRα mutants is not solely characterised by a constitutive activation of the conventional PDGFRα signalling pathways. In contrast to wild-type PDGFRα signal transduction, the activation of STAT factors (STAT1, STAT3 and STAT5) is an integral part of signalling mediated via mutated PDGF-receptors. Furthermore, this unconventional STAT activation by mutated PDGFRα is already initiated in the endoplasmic reticulum whereas the conventional signalling pathways rather require cell surface expression of the receptor. Finally, we demonstrate that the activation of STAT factors also translates into a biologic response as highlighted by the induction of STAT target genes. CONCLUSION: We show that the overall oncogenic response is the result of different signatures emanating from different cellular compartments. Furthermore, STAT mediated responses are an integral part of mutated PDGFRα signalling.

Interleukin-27 displays interferon-gamma-like functions in human hepatoma cells and hepatocytes.

UNLABELLED: Interleukin-27 (IL-27) is a cytokine belonging to the IL-6/IL-12 cytokine family. It is secreted by antigen-presenting cells, strongly acts on T cells, and also stimulates innate immune cells. In most studies, the effects of IL-27 on T cells were investigated; however, not much is known about possible effects of IL-27 on other cell types. IL-27 signals via the common IL-6-type cytokine receptor chain gp130 and the IL-27-specific chain WSX-1. Given the importance of gp130 in regulating liver responses such as the acute phase response or liver regeneration, we investigated whether IL-27 could also have a function in liver cells. We find that IL-27 stimulates hepatoma cells and hepatocytes by inducing a sustained signal transducer and activator of transcription (STAT)1 and STAT3 activation. Whereas the STAT3 mediated responses to IL-27 (gamma-fibrinogen and hepcidin induction) are not detectable, we observe an interferon-gamma (IFN-gamma)-like STAT1 response leading to the induction of interferon-regulated proteins such as STAT1, STAT2, interferon response factor (IRF)-1, IRF-9, myxovirus resistance A and guanylate binding protein 2. CONCLUSION: Our study provides evidence for a function of IL-27 in hepatoma cells and hepatocytes and shows that IL-27 responses are not restricted to the classical immune cells. Our results suggest that IL-27 exerts IFN-like functions in liver cells and that it can contribute to the antiviral response in these cells.

Development of an IL-6 inhibitor based on the functional analysis of murine IL-6Ralpha(1).

Dysregulated cytokine production contributes to inflammatory and proliferative diseases. Therefore, inhibition of proinflammatory mediators such as TNF, IL-1, and IL-6 is of great clinical relevance. Actual strategies are aimed at preventing receptor activation through sequestration of the ligand. Here we describe the development of an inhibitor of murine IL-6 based on fused receptor fragments. Molecular modeling-guided analysis of the murine IL-6Ralpha revealed that mutations in the Ig-like domain D1 severely affect protein function, although D1 is not directly involved in the ligand-binding interface. The resulting single chain IL-6 inhibitor (mIL-6-RFP) consisting of domains D1-D3 of mgp130, a flexible linker, and domains D1-D3 of mIL-6Ralpha is a highly potent and specific IL-6 inhibitor. mIL-6-RFP will permit further characterization of the role of IL-6 in various disease models and could ultimately lead to anti-IL-6 therapy.