Interleukin-one induced inositol phospholipid breakdown in murine macrophages: possible mechanism of receptor activation.

Stimulation of mouse peritoneal macrophages by Interleukin-one (IL-1) provoked rapid increases in the levels of inositol mono, bis, tris and tetrakisphosphates (IP1, IP2, IP3 and IP4 respectively). IP3 was by far the major metabolite formed and time course studies revealed that IP2 and IP3 were formed more rapidly than IP1 and IP4 in response to IL-1 stimulation. The IP2 and IP3 levels peaked at five seconds while there was a time lag of five seconds in the IP4 response and the IP1 levels increased relatively steadily over the time course of the experiments. Levels of IP2, IP3 and IP4 all returned almost to control levels by 60s. The rapid formation of the inositol phosphate metabolites was concomitant with a decrease (84%) in the levels of phosphatidyl-inositol 4,5-bisphosphate (PIP2) in the macrophages. These results suggest that the mechanism of IL-1 receptor activation is by the rapid hydrolysis of phosphoinositides and generation of the second messenger IP3.