The proto-oncogene c-Cbl is a negative regulator of DNA synthesis initiated by both receptor and cytoplasmic tyrosine kinases.
In C. elegans, genetic and biochemical data indicate that the Cbl homolog Sli-1 attenuates Let-23 (EGFR) signaling. To investigate whether c-Cbhl might have a role in mammalian growth factor-mediated mitogenic signaling, we microinjected NIH3T3 mouse fibroblasts with expression plasmids encoding wt and G306ECbl (a 'loss of function' mutant identified in C. elegans). We observed inhibition of PDGF BB- and EGF-induced DNA synthesis by wt Cbl but not the mutant. Microinjection of two different affinity purified polyclonal antisera against Cbl boosted a suboptimal PDGF-stimulated mitogenic response. The inhibition of both PDGF BB- and EGF-induced DNA synthesis by wt Cbl was reversed by co-expression with Myc but not with Fos. DNA synthesis initiated by constitutively activated Src was also blocked by Cbl expression, but curiously by the G306E mutant as well. These data are all consistent with the proposition that Cbl negatively affects mitogenic signaling in mammalian fibroblasts.
Broome
M A
MA
SUGEN, Inc., South San Francisco, California 94080, USA.
Galisteo
M L
ML
Schlessinger
J
J
Courtneidge
S A
SA
D016475:3T3 Cells / Q000187:drug effects / Q000378:metabolism; D000818:Animals; D001973:Bromodeoxyuridine / Q000378:metabolism; D002460:Cell Line; D003593:Cytoplasm / Q000201:enzymology*; D004247:DNA / Q000096:biosynthesis*; D004815:Epidermal Growth Factor / Q000378:metabolism / Q000494:pharmacology; D016762:Genes, fos; D016259:Genes, myc; D016391:Genes, src; D006388:Hemagglutinins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D007106:Immune Sera; D015151:Immunoblotting; D051379:Mice; D009154:Mutation; D010982:Platelet-Derived Growth Factor / Q000378:metabolism / Q000494:pharmacology; D000090063:Proto-Oncogene Mas; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D050721:Proto-Oncogene Proteins c-cbl; D011817:Rabbits; D020794:Receptor Protein-Tyrosine Kinases / Q000378:metabolism*; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D044767:Ubiquitin-Protein Ligases
D006388:Hemagglutinins; D007106:Immune Sera; C000715470:MAS1 protein, human; D010982:Platelet-Derived Growth Factor; D000090063:Proto-Oncogene Mas; D011518:Proto-Oncogene Proteins; D011994:Recombinant Proteins; D004815:Epidermal Growth Factor; D004247:DNA; D050721:Proto-Oncogene Proteins c-cbl; D044767:Ubiquitin-Protein Ligases; D020794:Receptor Protein-Tyrosine Kinases; C067419:CBL protein, human; C493849:Cbl protein, mouse; D001973:Bromodeoxyuridine