Colony‐stimulating factor 1 (CSF‐1) is required for the survival, proliferation and differentiation of monocytes. We previously demonstrated that the CSF‐1 receptor is linked to a pertussis toxin‐sensitive G protein and that the induction of Na+ influx by CSF‐1 is a pertussis toxin‐sensitive event. The present studies have examined activation of protein kinase C as a potential intracellular signaling event induced by the activated CSF‐1 receptor. The results demonstrate that CSF‐1 stimulates translocation of protein kinase C activity from the cytosol to membrane fractions. This activation of protein kinase C was sensitive to pretreatment of the monocytes with pertussis toxin. Lipid distribution studies demonstrated that phosphatidylcholine (PC) is the major phospholipid in human monocytes. Moreover, the results indicate that CSF‐1 stimulation is associated with decreases in PC, but not in phosphatidylinositol (PI), levels. The absence of an effect of CSF‐1 on PI turnover was confirmed by the lack of changes in inositol phosphate production. In contrast, CSF‐1 stimulation was associated with increased hydrolysis of PC to phosphorylcholine and diacylglycerol (DAG) in both intact monocytes and cell‐free assays. Furthermore, the increase in PC turnover induced by CSF‐1 was sensitive to pertussis toxin. The results also demonstrate that the induction of Na+ influx by CSF‐1 is inhibited by the protein kinase C inhibitors staurosporine and the isoquinoline derivative H7, but not by HA1004.(ABSTRACT TRUNCATED AT 250 WORDS)
Macrophage colony-stimulating factor (M-CSF) is required for the proliferation, differentiation, and activation of monocytes. High- affinity receptors for M-CSF are encoded by the c-fms proto-oncogene. In the present study, we show that c-fms transcripts are detectable in human THP-1 myeloid leukemia cells. Furthermore, radiolabeled 125I-M- CSF is rapidly internalized into THP-1 cells and then degraded intracellularly. The results also show that treatment of THP-1 cells with M-CSF is associated with the activation of protein kinase C (PKC) and the induction of tumor necrosis factor (TNF) gene expression. TNF transcript levels were low to undetectable in uninduced THP-1 cells, reached maximal levels by 1 hour of exposure to M-CSF, and returned to those of control cells by 24 hours. Transcriptional run-on analysis showed that a low level of TNF transcription is detectable in untreated THP-1 cells, and M-CSF treatment increased the rate of TNF transcription. Pretreatment of THP-1 cells with pertussis toxin inhibited the increase in PKC activity but not the induction of TNF transcripts by M-CSF. Moreover, exposure of THP-1 cells to inhibitors of protein kinase activity blocked the increase in TNF messenger RNA. These findings suggest that at least two M-CSF-mediated signaling pathways exist in THP-1 cells and that the induction of TNF may be regulated by a protein kinase-dependent mechanism distinct from PKC.
Macrophage colony-stimulating factor (M-CSF) is required for the proliferation, differentiation, and activation of monocytes. High- affinity receptors for M-CSF are encoded by the c-fms proto-oncogene. In the present study, we show that c-fms transcripts are detectable in human THP-1 myeloid leukemia cells. Furthermore, radiolabeled 125I-M- CSF is rapidly internalized into THP-1 cells and then degraded intracellularly. The results also show that treatment of THP-1 cells with M-CSF is associated with the activation of protein kinase C (PKC) and the induction of tumor necrosis factor (TNF) gene expression. TNF transcript levels were low to undetectable in uninduced THP-1 cells, reached maximal levels by 1 hour of exposure to M-CSF, and returned to those of control cells by 24 hours. Transcriptional run-on analysis showed that a low level of TNF transcription is detectable in untreated THP-1 cells, and M-CSF treatment increased the rate of TNF transcription. Pretreatment of THP-1 cells with pertussis toxin inhibited the increase in PKC activity but not the induction of TNF transcripts by M-CSF. Moreover, exposure of THP-1 cells to inhibitors of protein kinase activity blocked the increase in TNF messenger RNA. These findings suggest that at least two M-CSF-mediated signaling pathways exist in THP-1 cells and that the induction of TNF may be regulated by a protein kinase-dependent mechanism distinct from PKC.
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