Characterisation of γ-interferon responsive promoters in fish

Reporter constructs of three interferon (IFN)-γ-induced rainbow trout genes were generated to examine specificity to type I or type II IFN. Constructs included γIP-10, LMP2 and TAP2 and were used to transfect trout fibroblast cells (RTG-2) which were then exposed to rainbow trout rIFNs. The γIP-10 construct showed high reporter activity even in the absence of rIFNs. The LMP2 promoter contained one GAS element and two double ISRE elements, of four constructs made, only those with ISRE elements showed significant reporter activity following rIFN-γ stimulation. The TAP2 regulatory region contained two GAS, two ISRE and one C/EBP element from which four constructs were made. Reporter expression for the construct containing all five elements showed an 11- and 2-fold increase in response to rIFN-γ and type I rIFN, respectively. Constructs containing only the GAS elements did not respond to rIFNs. The TAP2 construct with two ISRE and the C/EBP gave the greatest dose-dependent reporter response to rIFN-γ, with no significant response to type I rIFN. These data suggest that the ISRE elements, or elements nearby, are essential for the induction of type II IFN responsive genes in trout. The TAP2 construct is a candidate to develop a IFN-γ reporter stable cell line.