EXPRESSION OF G-ALPHA(I2) MIMICS SEVERAL ASPECTS OF LPS PRIMING IN A MURINE MACROPHAGE-LIKE CELL-LINE

Priming of macrophages with low concentrations of lipopolysaccharide ( LPS) enhances the ability of substances that act through heterotrimeri c G proteins to stimulate immune cell functions. Although LPS-induced alterations in the expression and functions of G proteins of the alpha (i) family have been reported in hematopoietic cells, their effects on subsequent steps in LPS priming of macrophages have not been defined. To study the role of G alpha(i2) in priming of macrophages by LPS, we expressed a mutant, activated form of alpha(i2) (alpha(i2Q205L)) in P 388D(1) cells, and compared its effects on PAF-dependent Ca signalling and arachidonic acid release to those in cells treated with LPS. In c ontrol P388D, cells, treatment with LPS (100 ng/ml) for 1 hr increased the amount of alpha(i2) protein 2-fold. Both LPS treatment and expres sion of alpha(i2Q205L). increased the rate of PAF-induced Ca influx ac ross the cell membrane and arachidonic acid release, although neither altered release of Ca from intracellular stores by PAF. Expression of alpha(i2Q205L) is sufficient to mimic the effects of LPS on the PAF-in duced C alpha(i) signal and enhanced arachidonic acid release. Consequ ently, although increasing the expression of alpha(i2) may not be the sole mechanism by which LPS enhances signalling by PAF, increased alph a(i2) expression can account for the alterations in PAF-induced Ca-i r egulation, and arachidonic acid release in LPS-primed P388D, cells. (C ) 1995 Wiley-Liss, Inc.