Rat p67 GBP is induced by interferon-gamma and isoprenoid-modified in macrophages

The guanylate binding proteins, GBPs, are a family of interferon-induced GTP-binding proteins that include the rat p67. We report here that rat p67, for which interferon regulation had not previously been demonstrated, is induced by IFN-gamma and also by LPS in both cultured bone marrow-derived macrophages and microglia. The basal level of rat p67 in macrophages is low but increases dramatically between 2 and 4 hours after treating cells with either IFN-gamma or LPS. It then remains elevated over the next 24 hours. Rat p67 is isoprenoid modified. The isoprenoid modification was detected in p67 isolated both from primary IFN-gamma-activated macrophages and when the gene for p67 was transfected into COS cells. This is the first demonstration of in vivo prenylation of a GBP. The interferon regulation and prenylation of rat p67 point toward this protein being significant in the functions of both activated macrophages and microglia.