c-Myc cooperates with activated Ras to induce the cdc2 promoter.
Expression of c-myc with constitutively active mutants of the ras gene results in the cooperative transformation of primary fibroblasts, although the precise mechanism by which these genes cooperate is unknown. Since c-Myc has been shown to function as a transcriptional activator, we have examined the ability of c-Myc and activated Ras (H-RasV-12) to cooperatively induce the promoter activity of cdc2, a gene which is critical for cell cycle progression. Microinjection of expression constructs encoding H-RasV-12 and c-Myc along with a cdc2 promoter-luciferase reporter plasmid into quiescent cells led to an increase in cdc2 promoter activity approximately 30 h after injection, a period which coincides with the S-to-G2/M transition in these cells. Expression of H-RasV-12 alone weakly activated the cdc2 promoter, while expression of c-Myc alone had no effect. Mutants of c-Myc lacking either the leucine zipper dimerization domain or the phosphoacceptor site Ser-62 could not cooperate with H-RasV-12 to induce the cdc2 promoter. These mutants also lacked the ability to cooperate with H-RasV-12 to stimulate DNA synthesis. Deletion analysis identified a distinct region of the cdc2 promoter which was required for c-Myc responsiveness. Taken together, these observations suggest a mechanistic link between the molecular activities of c-Myc and Ras and induction of the cell cycle regulator Cdc2.
Born
T L
TL
Department of Medicine, University of California, San Diego, La Jolla 92093-0636.
Frost
J A
JA
Schönthal
A
A
Prendergast
G C
GC
Feramisco
J R
JR
D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D016203:CDC2 Protein Kinase / Q000096:biosynthesis*; D002453:Cell Cycle; D005786:Gene Expression Regulation; D016259:Genes, myc; D006801:Humans; D066298:In Vitro Techniques; D016350:Leucine Zippers; D046911:Macromolecular Substances; D008969:Molecular Sequence Data; D010768:Phosphoserine / Q000378:metabolism; D011401:Promoter Regions, Genetic; D016271:Proto-Oncogene Proteins c-myc / Q000737:chemistry / Q000378:metabolism*; D016283:Proto-Oncogene Proteins p21(ras) / Q000378:metabolism*; D051381:Rats; D013329:Structure-Activity Relationship; D015533:Transcriptional Activation
D046911:Macromolecular Substances; D016271:Proto-Oncogene Proteins c-myc; D010768:Phosphoserine; D016203:CDC2 Protein Kinase; C501009:HRAS protein, human; D016283:Proto-Oncogene Proteins p21(ras)