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Genetic and epigenetic alterations in lung tumors from bitransgenic Ki‐ ras G12C expressing mice
Author(s) -
Floyd Heather S.,
JenningsGee Jamie E.,
Kock Nancy D.,
Miller Mark Steven
Publication year - 2006
Publication title -
molecular carcinogenesis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.254
H-Index - 97
eISSN - 1098-2744
pISSN - 0899-1987
DOI - 10.1002/mc.20181
Subject(s) - biology , survivin , cyclin d1 , cancer research , immunohistochemistry , retinoblastoma , adenocarcinoma , pathology , cyclin , tumor suppressor gene , lung , gene expression , microbiology and biotechnology , adenoma , cell cycle , gene , carcinogenesis , cancer , medicine , immunology , biochemistry , genetics
Mutations in Ki‐ ras occur in approximately 30–50% of patients with adenocarcinoma (AC) of the lung. We previously reported the development of a bitransgenic mouse model that expressed the human Ki‐ ras G12C allele in a lung‐specific, tetracycline‐inducible manner and gave rise to benign lung tumors. In the current study, these benign tumors, which represent relatively early lesions in neoplastic progression, were analyzed for molecular alterations secondary to mutant Ki‐ ras expression to determine the gene(s) that contribute to adenoma (AD) development. Tumors were removed following doxycycline (DOX) treatment for 9 and 12 mo and examined for alterations in cell‐cycle regulatory genes. Quantification of mRNA expression for cyclin D1, retinoblastoma, p16 Ink4a , p19 Arf , and survivin was carried out by real‐time PCR. All of the tumors examined exhibited a mean reduction of approximately fivefold for the retinoblastoma gene ( P < 0.02). Increased expression of both p19 Arf and survivin were detected in a majority of the tumors examined ( P < 0.01 and 0.001, respectively), but no change in cyclin D1 RNA expression was observed. A subset of the lung tumors (8/28) displayed reduced levels of p16 Ink4a expression ( P = 0.02). Immunohistochemical analysis confirmed the upregulation of p19 Arf and survivin in all 10 of the lung tumors examined. However, increased staining for cyclin D1 was observed in the tumor tissue. In addition, increased levels of activated p53 were found in lung tumor tissues stained with an anti‐phospho‐ p53 antibody, while an absence of staining was observed with an anti‐phospho‐pRb antibody in both normal control and tumor tissue. Analysis of the methylation status of p16 Ink4a by methylation‐specific PCR (MSP) demonstrated that seven of eight tumors exhibiting decreased expression of p16 Ink4a had at least partial methylation of the promoter region. Single stranded conformational polymorphism (SSCP) analysis demonstrated that neither exons 1 or 2 of p16 Ink4a nor exons 5–8 of p53 exhibited mutations. These data thus identify alterations in specific genes and pathways that combine with the mutation in Ki‐ ras to promote the formation of benign lung tumors and suggest potential targets for the development of novel chemotherapeutic and chemopreventive agents during the early stages of lung tumor progression. © 2006 Wiley‐Liss, Inc.