Glioblastoma-related gene mutations and over-expression of functional epidermal growth factor receptors in SKMG-3 glioma cells.
Amplification of the epidermal growth factor receptor (EGFR) gene is found in about 40% of glioblastomas (GBMs) but is rarely detected in GBM cell lines. We confirmed that the exceptional SKMG-3 GBM cell line retained amplified EGFR genes in vitro, and found that these sequences were concentrated on extra-chromosomal DNA particles similar to double-minute chromosomes. The cells contained two other gene mutations that are associated with high-grade astrocytic tumors: extra-chromosomal amplification of the cyclin-dependent kinase-4 (CDK4) gene and a homozygous mutation within the PTEN tumor suppressor gene. Immunoblots revealed very high levels of EGFR, moderately increased expression of CDK4, and no detectable PTEN protein. The overexpressed SKMG-3 EGFRs responded to exogenous ligand and resembled normal rather than mutant receptors. A heterozygous mutation of the p53 gene (p53R282W) correlated with failure of radiation to induce the expression of cyclin-dependent kinase inhibitor p21waf1 or an early G1 cell cycle arrest. Although each of these gene mutations occurs in GBMs, SKMG-3 cells had an unusual genotype in that a p53 gene mutation co-existed with amplified EGFR genes. Nonetheless, the SKMG-3 cell line can be exploited as a model to study how oncogenic EGFR signals in GBM cells interact with over-expressed CDK4 and loss of PTEN to confer the malignant phenotype.
Thomas
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Mayo Clinic-Jacksonville, Mayo Medical School, Division of Hematology/Oncology, Jacksonville, FL 32224, USA. thomc6@mayo.edu
Ely
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James
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Jenkins
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Kastan
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Jedlicka
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A
Burger
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Wharen
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D015139:Blotting, Southern; D001932:Brain Neoplasms / Q000235:genetics*; D018844:Cyclin-Dependent Kinases / Q000096:biosynthesis / Q000235:genetics; D066246:ErbB Receptors / Q000096:biosynthesis* / Q000235:genetics*; D005434:Flow Cytometry; D015972:Gene Expression Regulation, Neoplastic / Q000235:genetics*; D016158:Genes, p53 / Q000235:genetics; D005838:Genotype; D005909:Glioblastoma / Q000235:genetics*; D006801:Humans; D017403:In Situ Hybridization; D009154:Mutation / Q000235:genetics*; D010641:Phenotype; D015398:Signal Transduction / Q000235:genetics; D014407:Tumor Cells, Cultured
D066246:ErbB Receptors; D018844:Cyclin-Dependent Kinases