RESUMO
The nervous system of the B6C3F1 mouse has rarely been a target for chemical carcinogenesis in the National Toxicology Program (NTP) bioassays. However, 6 malignant gliomas and 2 neuroblastomas were observed in B6C3F1 mice exposed to 625 ppm 1,3-butadiene (NTP technical reports 288 and 434). These mouse brain tumors were evaluated with regard to the profile of genetic alterations that are observed in human brain tumors. Alterations in the p53 tumor suppressor gene were common. Missense mutations were observed in 3/6 malignant gliomas and 2/2 neuroblastomas and were associated with loss of heterozygosity. Most of the mutations occurred in exons 5-8 of the p53 gene and were G-->A transitions, and did not involve CpG sites. Loss of heterozygosity at the Ink4a/Arf gene locus was observed in 5/5 malignant gliomas and 1/1 neuroblastoma, while the PTEN(phosphatase and tensin homologue) gene locus was unaffected by deletions. One of 2 neuroblastomas had a mutation in codon 61 of H-ras, while H-ras mutations were not observed in the malignant gliomas examined. Only 1 brain tumor has been reported from control mice of over 500 NTP studies. This malignant glioma showed no evidence of alterations in the p53 gene or K- and H-ras mutations. It is likely that the specific genetic alterations observed were induced or selected for by 1,3-butadiene treatment that contributed to the development of mouse brain tumors. The observed findings are similar in part to the genetic alterations reported in human brain tumors.
Assuntos
Neoplasias Encefálicas/genética , Butadienos/toxicidade , Carcinógenos/toxicidade , Glioma/genética , Neuroblastoma/genética , Animais , Neoplasias Encefálicas/induzido quimicamente , Neoplasias Encefálicas/patologia , Códon , DNA de Neoplasias/genética , DNA de Neoplasias/isolamento & purificação , Relação Dose-Resposta a Droga , Éxons , Feminino , Deleção de Genes , Glioma/induzido quimicamente , Glioma/patologia , Imuno-Histoquímica , Perda de Heterozigosidade , Masculino , Camundongos , Camundongos Endogâmicos , Mutação de Sentido Incorreto , Neuroblastoma/induzido quimicamente , Neuroblastoma/patologia , Reação em Cadeia da Polimerase , Proteína Supressora de Tumor p53/efeitos dos fármacos , Proteína Supressora de Tumor p53/genéticaRESUMO
Amplification of the epidermal growth factor receptor (EGFR) or expression of its constitutively activated mutant, DeltaEGFR(2-7), in association with the inactivation of the INK4a/Arf gene locus is a frequent alteration in human glioblastoma. The notion of a cooperative effect between these two alterations has been demonstrated in respective mouse brain tumor models including our own. Here, we investigated underlying molecular mechanisms in early passage cortical astrocytes deficient for p16(INK4a)/p19(Arf) or p53, respectively, with or without ectopic expression of DeltaEGFR(2-7). Targeting these cells with the specific EGFR inhibitor tyrphostin AG1478 revealed that phosphorylation of ERK was only abrogated in the presence of an intact INK4a/Arf gene locus. The sensitivity to inhibit ERK phosphorylation was independent of ectopic expression of DeltaEGFR(2-7) and independent of the TP53 status. This resistance to downregulate the MAPK pathway in the absence of INK4a/Arf was confirmed in cell lines derived from our mouse glioma models with the respective initial genetic alterations. Thus, deletion of INK4a/Arf appears to keep ERK in its active, phosphorylated state insensitive to an upstream inhibitor specifically targeting EGFR/DeltaEGFR(2-7). This resistance may contribute to the cooperative tumorigenic effect selected for in human glioblastoma that may be of crucial clinical relevance for treatments specifically targeting EGFR/DeltaEGFR(2-7) in glioblastoma patients.
