Loss of heterozygosity of chromosome 12p does not correlate with KRAS mutation in non-small cell lung cancer.
Activating mutations of RAS gene families have been found in a variety of human malignancies, including lung cancer, suggesting their dominant role in tumorigenesis. However, several studies have shown a frequent loss of the wild-type KRAS allele in the tumors of murine models and an inhibition of oncogenic phenotype in tumor cell lines by transfection of wild-type RAS, indicating that wild-type RAS may have oncosuppressive properties. To determine whether loss of wild-type KRAS is involved in the development of human lung cancer, we investigated the mutations of KRAS, NRAS and BRAF in 154 primary non-small cell lung cancers (NSCLCs) as well as 10 NSCLC cell lines that have been shown to have KRAS mutations. We also determined the loss of heterozygosity status of KRAS alleles in these tumors. We detected point mutations of KRAS in 11 (7%) of 154 NSCLCs, with 10 cases at codon 12 and 1 at codon 61, but no mutations of NRAS or BRAF were found. Using the laser capture microdissection technique, we confirmed that 9 of the 11 tumors and 7 of the 10 NSCLC cell lines retained the wild-type KRAS allele. Among the cell lines with heterozygosity of mutant and wild-type KRAS, all of the cell lines tested for expression were shown to express more mutated KRAS than wild-type mRNA, with higher amounts of KRAS protein also being expressed compared to the cell lines with a loss of wild-type KRAS allele. In addition, among 148 specimens available for immunohistochemical analysis, 113 (76%) showed positive staining of KRAS, indicating that the vast majority of NSCLCs continue to express wild-type KRAS. Our findings indicate that the wild-type KRAS allele is occasionally lost in human lung cancer, and that the oncogenic activation of mutant KRAS is more frequently associated with an overexpression of the mutant allele than with a loss of the wild-type allele in human NSCLC development.
Department of Clinical Preventive Medicine, Nagoya University School of Medicine, Tsurumai 65, Showa-ku, Nagoya 466-8560, Japan.
Mika
M
Uchiyama
Noriyasu
N
Usami
Masashi
M
Kondo
Shoichi
S
Mori
Masao
M
Ito
Genshi
G
Ito
Hiromu
H
Yoshioka
Munehisa
M
Imaizumi
Yuichi
Y
Ueda
Masahide
M
Takahashi
John D
JD
Minna
Kaoru
K
Shimokata
Yoshitaka
Y
Sekido
D001483:Base Sequence; D002289:Carcinoma, Non-Small-Cell Lung / Q000145:classification / Q000235:genetics* / Q000473:pathology; D002874:Chromosome Mapping; D002881:Chromosomes, Human, Pair 12 / Q000235:genetics*; D017931:DNA Primers; D005091:Exons; D005260:Female; D011905:Genes, ras / Q000235:genetics*; D005819:Genetic Markers; D006579:Heterozygote; D006801:Humans; D019656:Loss of Heterozygosity / Q000235:genetics*; D008175:Lung Neoplasms / Q000235:genetics* / Q000473:pathology; D008297:Male; D008875:Middle Aged; D009367:Neoplasm Staging; D014407:Tumor Cells, Cultured
D017931:DNA Primers; D005819:Genetic Markers