ABSTRACT
Ubiquitous expression of a resident K-Ras(G12V) oncogene in adult mice revealed that most tissues are resistant to K-Ras oncogenic signals. Indeed, K-Ras(G12V) expression only induced overt tumors in lungs. To identify these transformation-permissive cells, we induced K-Ras(G12V) expression in a very limited number of adult lung cells (0.2%) and monitored their fate by X-Gal staining, a surrogate marker coexpressed with the K-Ras(G12V) oncoprotein. Four weeks later, 30% of these cells had proliferated to form small clusters. However, only SPC(+) alveolar type II (ATII) cells were able to form hyperplastic lesions, some of which progressed to adenomas and adenocarcinomas. In contrast, induction of K-Ras(G12V) expression in lung cells by intratracheal infection with adenoviral-Cre particles generated hyperplasias in all regions except the proximal airways. Bronchiolar and bronchioalveolar duct junction hyperplasias were primarily made of CC10(+) Clara cells. Some of them progressed to form benign adenomas. However, only alveolar hyperplasias, exclusively made up of SPC(+) ATII cells, progressed to yield malignant adenocarcinomas. Adenoviral infection induced inflammatory infiltrates primarily made of T and B cells. This inflammatory response was essential for the development of K-Ras(G12V)-driven bronchiolar hyperplasias and adenomas, but not for the generation of SPC(+) ATII lesions. Finally, activation of K-Ras(G12V) during embryonic development under the control of a Sca1 promoter yielded CC10(+), but not SPC(+), hyperplasias, and adenomas. These results, taken together, illustrate that different types of lung cells can generate benign lesions in response to K-Ras oncogenic signals. However, in adult mice, only SPC(+) ATII cells were able to yield malignant adenocarcinomas.
Subject(s)
Adenocarcinoma/metabolism , Gene Expression Regulation, Neoplastic , Genes, ras , Lung Neoplasms/metabolism , Lung/cytology , ras Proteins/metabolism , Adenocarcinoma/genetics , Adenocarcinoma of Lung , Adenoviridae/metabolism , Alleles , Animals , Bronchioles/metabolism , Carcinoma, Non-Small-Cell Lung/metabolism , Cell Proliferation , Cell Separation , Cell Transformation, Neoplastic , Flow Cytometry , Gene Expression Profiling , Inflammation , Lung Neoplasms/genetics , Mice , Mice, Transgenic , Oncogenes , Promoter Regions, Genetic , Pulmonary Alveoli/metabolism , Signal Transduction , Stem Cells/cytologyABSTRACT
Protein farnesyltransferase (FTase) is an enzyme responsible for posttranslational modification of proteins carrying a carboxy-terminal CaaX motif. Farnesylation allows substrates to interact with membranes and protein targets. Using gene-targeted mice, we report that FTase is essential for embryonic development, but dispensable for adult homeostasis. Six-month-old FTase-deficient mice display delayed wound healing and maturation defects in erythroid cells. Embryonic fibroblasts lacking FTase have a flat morphology and reduced motility and proliferation rates. Ablation of FTase in two ras oncogene-dependent tumor models has no significant consequences for tumor initiation. However, elimination of FTase during tumor progression had a limited but significant inhibitory effect. These results should help to better understand the role of protein farnesylation in normal tissues and in tumor development.
Subject(s)
Alkyl and Aryl Transferases/physiology , Embryonic Development/physiology , Homeostasis/physiology , Neoplasms/enzymology , Tamoxifen/analogs & derivatives , Alkyl and Aryl Transferases/genetics , Alkyl and Aryl Transferases/metabolism , Animals , Cell Proliferation , Embryo Loss/genetics , Embryo Loss/pathology , Embryo, Mammalian/metabolism , Embryo, Mammalian/pathology , Embryonic Development/genetics , Erythroid Cells/enzymology , Erythroid Cells/pathology , Estrogen Antagonists/pharmacology , Fibroblasts/enzymology , Fibroblasts/pathology , Gene Expression/drug effects , Gene Expression/genetics , Integrases/genetics , Liver/enzymology , Liver/pathology , Lung/enzymology , Lung/pathology , Mice , Mice, Knockout , Mutation/genetics , Neoplasms/genetics , Neoplasms/pathology , Skin Neoplasms/enzymology , Skin Neoplasms/genetics , Skin Neoplasms/pathology , Spleen/pathology , Tamoxifen/pharmacology , Wound Healing/genetics , Wound Healing/physiology , ras Proteins/genetics , ras Proteins/metabolismABSTRACT
We have targeted a K-ras allele in mouse embryonic stem (ES) cells to express a K-Ras(V12) oncoprotein along with a marker protein (beta-geo) from a single bicistronic transcript. Expression of this oncogenic allele requires removal of a knocked in STOP transcriptional cassette by Cre recombinase. Primary mouse embryonic fibroblasts expressing this K-ras(V12) allele do not undergo proliferative senescence and proliferate as immortal cells. In mice, expression of K-ras(V12) throughout the body fails to induce unscheduled proliferation or other growth abnormalities for up to eight months. Only a percentage of K-ras(V12)-expressing lung bronchiolo-alveolar cells undergo malignant transformation leading to the formation of multiple adenomas and adenocarcinomas. These results indicate that neoplastic growth induced by an endogenous K-ras oncogene depends upon cellular context.
