Priming of Mouse Macrophages with the Macrophage Colony-Stimulating Factor (CSF-1) Induces a Variety of Pathways That Regulate Expression of the Interleukin 6 (Il6) and Granulocyte–Macrophage Colony-Stimulating Factor (Csfgm) Genes

Abstract

Recent data have indicated that resident mouse peritoneal macrophages (PMø) transcribed the interleukin 6 (Il6) and granulocyte–macrophage colony-stimulating factor (Csfgm) genes in response to stimulation with the monocyte–macrophage colony-stimulating factor (CSF-1) but onlyIl6mRNA was translated into secreted protein. In this paper, we extend these observations. It is shown that resident PMø incubated with protein kinase (PK)C inhibitors, staurosporine (SP) and its derivative GF109203-X, showed a several fold increase in the levels ofIl6mRNA in control and CSF-1-primed PMø and a parallel release of large amounts of protein. In contrast, SP was shown to have no effect on the release of GM-CSF from control or CSF-1-primed PMø, although it increased by approximately twofold the amount ofCsfgmmRNA in CSF-1-primed Mø. When SP was added 4 h after CSF-1 priming to block CSF-1-induced protein kinase pathways, an increased amount of IL-6 release was again seen but without any increase inIl6mRNA levels. Under these conditions,Csfgmgene expression was relatively unaffected. Activation of PKC by phorbol myristate acetate (PMA) also resulted in increasedIl6gene expression by control and CSF-1-primed PMø. PMA had no apparent effect onCsfgmtranscription but appeared to influence translation at a low level, as measured by the release of small amounts of GM-CSF protein. The addition of lipopolysaccharide (LPS) to CSF-1-primed PMø resulted in a synergistic increase in the expression of both genes at the levels of transcription and protein release. The addition of SP to CSF-1-primed Mø before LPS, however, further enhanced IL-6 release but not GM-CSF release from the cells. The data indicate that CSF-1-priming drives a number of pathways involved in the regulation of expression of both genes and renders PMø highly susceptible to appropriate secondary stimulatory agents that transform the PMø into secretory inflammatory cells.