v-raf confers CSF-1 independent growth to a macrophage cell line and leads to immediate early gene expression without MAP-kinase activation.
The BAC-1.2F5 macrophage cell line depends on CSF-1 for proliferation and survival. Phosphorylation and activation of the RAF-1 kinase are among the early events in CSF-1 signal transduction. To characterize the role of RAF-1 in CSF-1-induced proliferation, we overexpressed oncogenically activated RAF-1, cellular RAF-1 and RAF-1 kinase-defective mutant proteins in BAC-1.2F5 cells. We were unable to establish stable cell lines expressing either kinase-negative or full length RAF-1 proteins, implying that expression of these molecules is not tolerated in BAC-1.2F5 cells. Oncogenically activated RAF-1 induces CSF-1-independent growth in the absence of autocrine growth factor production. Autonomous growth is not associated with dedifferentiation, since v-raf-expressing macrophages perform the same immunological functions as control cells. Intriguingly, autonomous growth correlates with the suppression of CSF-1-mediated MAP-Kinase activation and with the low constitutive expression of a number of CSF-1-inducible genes, including fos, jun, ets2, and myc, but also the genes for the inflammatory cytokines TNF alpha and IL-1 beta. Many of these genes have AP-1 binding sites in their promoters, and the v-raf-expressing cells contain constitutive AP-1 binding activity. These data indicate that RAF-1, but not MAP-Kinase, is a key component in CSF-1 mitogenic signal transduction, and are consistent with a working hypothesis in which RAF-1 mediates transcriptional activation of genes via AP-1.
Büscher
D
D
Department of Immunbiology, Fraunhofer Institute for Toxicology and Molecular Biology, Hannover, Germany.
Dello Sbarba
P
P
Hipskind
R A
RA
Rapp
U R
UR
Stanley
E R
ER
Baccarini
M
M
D000595:Amino Acid Sequence; D000818:Animals; D015152:Blotting, Northern; D015153:Blotting, Western; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000235:genetics / Q000378:metabolism*; D002454:Cell Differentiation / Q000502:physiology; D002455:Cell Division / Q000502:physiology; D002460:Cell Line; D002470:Cell Survival / Q000502:physiology; D004247:DNA / Q000235:genetics / Q000378:metabolism; D004789:Enzyme Activation; D005786:Gene Expression Regulation / Q000235:genetics*; D017781:Genes, Immediate-Early / Q000235:genetics*; D006133:Growth Substances / Q000378:metabolism; D006801:Humans; D016173:Macrophage Colony-Stimulating Factor / Q000378:metabolism / Q000502:physiology*; D008264:Macrophages / Q000166:cytology* / Q000502:physiology; D008969:Molecular Sequence Data; D009154:Mutation; D027384:Oncogene Proteins v-raf; D010766:Phosphorylation; D011233:Precipitin Tests; D016755:Proto-Oncogene Proteins c-jun / Q000378:metabolism / Q000502:physiology; D015682:Retroviridae Proteins, Oncogenic / Q000235:genetics* / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology; D014158:Transcription, Genetic / Q000235:genetics
D006133:Growth Substances; D016755:Proto-Oncogene Proteins c-jun; D015682:Retroviridae Proteins, Oncogenic; D016173:Macrophage Colony-Stimulating Factor; D004247:DNA; D027384:Oncogene Proteins v-raf; D017871:Calcium-Calmodulin-Dependent Protein Kinases