Maintenance of growth factor signaling through Ras in human colon carcinoma cells containing K-ras mutations.
Fifty percent of human colon carcinomas contain activating mutations in the K-ras gene. However, whether these alterations in K-ras affect the function of Ras proteins in growth factor (GF) signal transduction is now known. Here we have characterized a previously defined human colon carcinoma cell model system for K-ras gene mutations and for altered levels of Ras protein expression and have examined whether these alterations affect Ras function in GF signal transduction. Sequence analysis of PCR-amplified K-ras gene fragments indicated that among the more aggressive cell lines, four had a normal K-ras sequence, whereas 3 others (isolated from the same human tumor) contained a mutation at codon 13. In contrast, all 7 of the less aggressive cell lines contained a mutation at either codon 12 or 13. In addition to the presence of a K-ras mutation, one cell line expressed higher levels of the K-Ras protein and displayed elevated Ras-GTP loading (in the absence of GF addition) compared with the other cell lines examined. Despite these alterations, the mitogenic GF combination epidermal growth factor + insulin + transferrin resulted in an activation of Ras and extracellular signal-regulated kinase 2. Collectively, our results indicate that the malignant phenotype of the cell lines was not correlated with the presence of K-ras mutations or with higher levels of Ras protein expression. Furthermore, K-ras mutations, high levels of K-Ras protein expression, and elevated Ras-GTP loading, as they occur naturally in human colon carcinomas, do not abolish the function of Ras in GF signaling.
Buard
A
A
Department of Pharmacology, Pennsylvania State University College of Medicine, Hershey 17033, USA.
Zipfel
P A
PA
Frey
R S
RS
Mulder
K M
KM
D001483:Base Sequence; D015153:Blotting, Western; D002460:Cell Line; D003062:Codon; D003110:Colonic Neoplasms; D017931:DNA Primers; D004815:Epidermal Growth Factor / Q000494:pharmacology; D005091:Exons; D011905:Genes, ras; D006133:Growth Substances / Q000494:pharmacology*; D006160:Guanosine Triphosphate / Q000378:metabolism; D006801:Humans; D007328:Insulin / Q000494:pharmacology; D007700:Kinetics; D008969:Molecular Sequence Data; D017354:Point Mutation; D016133:Polymerase Chain Reaction; D015398:Signal Transduction; D014168:Transferrin / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D018631:ras Proteins / Q000096:biosynthesis / Q000502:physiology*
D003062:Codon; D017931:DNA Primers; D006133:Growth Substances; D007328:Insulin; D014168:Transferrin; D004815:Epidermal Growth Factor; D006160:Guanosine Triphosphate; D018631:ras Proteins