GTP gamma S inhibits early c-myc protein accumulation but not DNA synthesis in Swiss 3T3 fibroblasts.
Quiescent Swiss 3T3 fibroblasts stimulated with epidermal growth factor and insulin showed large transient increases in c-myc mRNA and c-myc protein accumulation which were maximal at about 2 h after addition of the co-mitogens. When the cells were loaded with 0.1 mM of guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S) by transient permeabilisation immediately before mitogenic stimulation, the increase in c-myc mRNA was similar to that observed in unloaded cells but the corresponding c-myc protein peak was reduced by at least 95%. The GTP gamma S completely blocked incorporation of [35S]methionine into cell proteins for 3-4 h after addition of the mitogens, but not thereafter, and caused a delay in the subsequent onset of DNA synthesis by the same period. The data show that less than 5% of the early increase in c-myc protein normally observed after mitogenic stimulation is required for its obligatory role in the progression of cells to S phase implied by other evidence.
Pennington
S R
SR
Department of Biochemistry, University of Cambridge, UK.
Moore
J P
JP
Evan
G I
GI
Hesketh
T R
TR
Metcalfe
J C
JC
D000818:Animals; D002460:Cell Line; D004261:DNA Replication / Q000187:drug effects*; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism; D016259:Genes, myc / Q000187:drug effects; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology*; D007700:Kinetics; D008715:Methionine / Q000378:metabolism; D051379:Mice; D016271:Proto-Oncogene Proteins c-myc / Q000096:biosynthesis* / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D013936:Thymidine / Q000378:metabolism; D014158:Transcription, Genetic / Q000187:drug effects
D016271:Proto-Oncogene Proteins c-myc; D012333:RNA, Messenger; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D008715:Methionine; D013936:Thymidine