The critical role of ERK in death resistance and invasiveness of hypoxia-selected glioblastoma cells.
BACKGROUND
The rapid growth of tumor parenchyma leads to chronic hypoxia that can result in the selection of cancer cells with a more aggressive behavior and death-resistant potential to survive and proliferate. Thus, identifying the key molecules and molecular mechanisms responsible for the phenotypic changes associated with chronic hypoxia has valuable implications for the development of a therapeutic modality. The aim of this study was to identify the molecular basis of the phenotypic changes triggered by chronic repeated hypoxia.


METHODS
Hypoxia-resistant T98G (HRT98G) cells were selected by repeated exposure to hypoxia and reoxygenation. Cell death rate was determined by the trypan blue exclusion method and protein expression levels were examined by western blot analysis. The invasive phenotype of the tumor cells was determined by the Matrigel invasion assay. Immunohistochemistry was performed to analyze the expression of proteins in the brain tumor samples. The Student T-test and Pearson Chi-Square test was used for statistical analyses.


RESULTS
We demonstrate that chronic repeated hypoxic exposures cause T98G cells to survive low oxygen tension. As compared with parent cells, hypoxia-selected T98G cells not only express higher levels of anti-apoptotic proteins such as Bcl-2, Bcl-X(L), and phosphorylated ERK, but they also have a more invasive potential in Matrigel invasion chambers. Activation or suppression of ERK pathways with a specific activator or inhibitor, respectively, indicates that ERK is a key molecule responsible for death resistance under hypoxic conditions and a more invasive phenotype. Finally, we show that the activation of ERK is more prominent in malignant glioblastomas exposed to hypoxia than in low grade astrocytic glial tumors.


CONCLUSIONS
Our study suggests that activation of ERK plays a pivotal role in death resistance under chronic hypoxia and phenotypic changes related to the invasive phenotype of HRT98G cells compared to parent cells.
Kim
Jee-Youn
JY
Brain Korea 21 Project Center, College of Medicine, Kyung Hee University, Seoul, Korea. falcon16@khu.ac.kr
Kim
Yong-Jun
YJ
Lee
Sun
S
Park
Jae-Hoon
JH
D051017:Apoptosis Regulatory Proteins / Q000235:genetics / Q000378:metabolism; D015687:Cell Hypoxia; D045744:Cell Line, Tumor; D048049:Extracellular Signal-Regulated MAP Kinases / Q000235:genetics / Q000378:metabolism*; D015972:Gene Expression Regulation, Neoplastic; D005909:Glioblastoma / Q000235:genetics / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology*; D006801:Humans; D009361:Neoplasm Invasiveness; D010100:Oxygen / Q000378:metabolism; D015398:Signal Transduction
D051017:Apoptosis Regulatory Proteins; D048049:Extracellular Signal-Regulated MAP Kinases; D010100:Oxygen