Relationship of c-myc gene copy number and gene expression: cellular effects of elevated c-myc protein.
The relationship between gene copy number and expression and cellular consequences of elevated levels of c-myc protein has been investigated using recombinant Chinese hamster ovary cell lines transfected with DNA coding for the murine c-myc gene. HC-8 and LC-5 recombinant cells carry approximately 800 and 50 copies of c-myc sequences, respectively, under control of an inducible heat shock promoter. Multivariate flow cytometric analysis and clonogenic assays were used to measure the relationship among c-myc expression, rate of DNA synthesis, and cell survival. Following heat exposure, maximally induced HC-8 cells produced approximately tenfold more c-myc protein than heated LC-5 cells, suggesting a close relationship between gene copy number and level of expression. However, considerable heterogeneity in the level and time of c-myc expression was observed following heat induction, even though the amounts of genomic c-myc were relatively constant. Heterogeneity in gene expression was not attributable to variation in heat induction methodologies and/or cell cycle phase distributions. The presence of high levels of recombinant c-myc protein was associated with a decreased rate of bromodeoxyuridine incorporation into DNA. High levels of c-myc protein in HC-8 cells were inversely correlated with cell survival postheating, suggesting that high levels of c-myc protein are incompatible with cell survival.
Biomedical Sciences Division, Lawrence Livermore National Laboratory, Livermore, California 94550.
M G
MG
Pallavicini
C
C
Rosette
M
M
Reitsma
P S
PS
Deteresa
J W
JW
Gray
D000818:Animals; D002460:Cell Line; D002470:Cell Survival; D006224:Cricetinae; D004247:DNA / Q000096:biosynthesis; D005434:Flow Cytometry; D005455:Fluorescent Antibody Technique; D005784:Gene Amplification; D015870:Gene Expression; D011518:Proto-Oncogene Proteins / Q000235:genetics*; D016271:Proto-Oncogene Proteins c-myc; D011994:Recombinant Proteins / Q000235:genetics
D011518:Proto-Oncogene Proteins; D016271:Proto-Oncogene Proteins c-myc; D011994:Recombinant Proteins; D004247:DNA