Differential activation of interferon responsive signalling pathways by type I and II interferons in parenchymal and non-parenchymal liver cells

The family of homologous type I interferons (IFN –α and –β) were originally identified for their potent antiviral activity but have also been shown to possess both antiproliferative and immunoregulatory properties. Both type I and type II interferons (IFN–γ) signal through distinct but related pathways, but still little is known about the specificity of interferon responses in different liver cells. We report here the differential activation of interferon responsive gene signalling pathways in murine parenchymal and non–parenchymal liver cells both on the transcriptional and translational level. To address this question we established a customized cDNA array comprising more than 80 known murine interferon stimulated genes (ISGs). Relevant data were confirmed by quantitative rt–PCR. Different signalling pathways were analysed by western blot.

IFN–α induces a number of ISGs (NOS 2, RNF4, IFIT1, Cxcl10) in murine Kupffer cells but not in liver sinusoidal endothelial cells (LSEC). Furthermore the expression of Cxcl10 is highly induced by interferon gamma (mIFN–γ) both in murine Kupffer cells and LSECs but only slightly in primary cultured mouse hepatocytes. Similiarly, several other ISGs were differentially induced in parenchymal and non–parenchymal liver cells (Ifi47), which are only expressed in Kupffer cells. Similar results can be obtained from Hepa 1_6 cells, in which these genes are activated by IFN–γ but in which these activation is completely inhibited by wortmannin, an inhibitor of the phosphoinositide3OHkinase (PI(3)k). Signal transducer and activator of transcription 1 (Stat1) is induced in parenchymal and non–parenchymal cells with different kinetics (maximum of activation in Kupffer cells after 5 min, in LSEC after 60 min). In addition, extracellular–signal regulated Kinase (ERK) was shown to be constitutively activated in Kupffer cells but not in LSECs.

In conclusion, these data indicate for the first time that type I and II interferons have differential effects on parenchymal and non-parenchymal liver cells which is of particular relevance for innate immune responses in the liver.

Keywords: ISG; interferon; signaltransduction pathway; parenchymal liver cells; mouse; murine; interferon stimulated gene; non-parenchymal liver cells