MEK–ERK-dependent multiple caspase activation by mitochondrial proapoptotic Bcl-2 family proteins is essential for heavy ion irradiation-induced glioma cell death

Abstract

Recently developed heavy ion irradiation therapy using a carbon beam (CB) against systemic malignancy has numerous advantages. However, the clinical results of CB therapy against glioblastoma still have room for improvement. Therefore, we tried to clarify the molecular mechanism of CB-induced glioma cell death. T98G and U251 human glioblastoma cell lines were irradiated by CB, and caspase-dependent apoptosis was induced in both cell lines in a dose-dependent manner. Knockdown of Bax (BCL-2-associated X protein) and Bak (BCL-2-associated killer) and overexpression of Bcl-2 or Bcl-xl (B-cell lymphoma-extra large) showed the involvement of Bcl-2 family proteins upstream of caspase activation, including caspase-8, in CB-induced glioma cell death. We also detected the activation of extracellular signal-regulated kinase (ERK) and the knockdown of ERK regulator mitogen-activated protein kinase kinase (MEK)1/2 or overexpression of a dominant-negative (DN) ERK inhibited CB-induced glioma cell death upstream of the mitochondria. In addition, application of MEK-specific inhibitors for defined periods showed that the recovery of activation of ERK between 2 and 36 h after irradiation is essential for CB-induced glioma cell death. Furthermore, MEK inhibitors or overexpression of a DN ERK failed to significantly inhibit X-ray-induced T98G and U251 cell death. These results suggested that the MEK–ERK cascade has a crucial role in CB-induced glioma cell death, which is known to have a limited contribution to X-ray-induced glioma cell death.

PARP inhibitor attenuated colony formation can be restored by MAP kinase inhibitors in different irradiated cancer cell lines

“…Several data obtained with regard to U251 cell line was found to be in line with those described by Tomiyama ' s group (Tomiyama et al 2010). However, we can report on the signifi cance of Erk1/2 activation in photon irradiation-induced glioblastoma cell death as well.…”

“…We are also aware of signal transduction element coding gene mutations having impact on anticancer therapy (McCubrey et al 2011). Besides, the Ras-Raf-MEK-Erk1/2 cascade, which is predominantly known as a promoter of cell viability, diff erentiation, survival and tumour progression, can play an undisputable role in cell death and inhibition of proliferation in U251 cell line (Arai et al 2004, Hagan et al 2007, Lu et al 2010, Tomiyama et al 2010. Th is fact is of outstanding signifi cance in cases like k-Ras Figure 7.…”

Downregulation of Ezh2 expression by RNA interference induces cell cycle arrest in the G0/G1 phase and apoptosis in U87 human glioma cells

“…These results indicate that the Ezh2 gene plays a key role in maintaining the growth and invasion of neuroblastoma. Studies have also shown that the apoptosis of glioma cells is closely related to the mitochondrial pathway (14,15). In this study, we showed that the silencing of the Ezh2 gene leads to changes in the levels of Bax and Bcl-2.…”

Differentiation-inducing effects of betamethasone on human glioma cell line U251

“…The current study showed that cell differentiation is a complex process with multiple stages, and may be related to multiple intracellular signal pathways, such as the ERK, PI3, K2A, KT, and Wnt signal pathways (Tomiyama et al, 2010). Of these pathways, the ERK signal pathway has the closest relationship with the proliferation and differentiation of tumor cells, and its activation is negatively correlated with tumor cell proliferation.…”