MOLECULAR-CLONING AND CHARACTERIZATION OF A MURINE LPS-INDUCIBLE CDNA

Murine macrophages respond to endotoxins by inducing a vast array of g enes that play a major role in the host's response to infection and tu mor growth. We have isolated and characterized a 1.8-kb cDNA, designat ed IRG2, from a cDNA library prepared from RNA isolated from the murin e cell line, RAW 264.7, after bacterial LPS stimulation. The cDNA enco des a protein of 47 kDa that is the murine homologue of a small family of proteins described from IFN-induced human cells. The IRG2 message does not appear until 3 h after LPS exposure and its induction is depe ndent on new protein synthesis. IRG2 induction by LPS is slightly inhi bited by the anti-inflammatory steroid, dexamethasone. Increasing cyto solic cAMP with either forskolin, dibutyrl cAMP, or 8-(4-chlorophenylt hio)-cAMP caused marked inhibition of the LPS induction of IRG2. In co ntrast, activation of PKC with phorbol ester potentiated the LPS respo nse. Removing extracellular Ca2+ with EGTA inhibited IRG2 induction; i ncreasing intracellular calcium with the calcium ionophore A23187 led to enhanced levels of the IRG2 transcript. These data suggest that the induction of IRG2 occurs via a PKC pathway.