Transcriptome analysis of glioma cells for the dynamic response to γ-irradiation and dual regulation of apoptosis genes: a new insight into radiotherapy for glioblastomas

H Ma,Z Y Yang,H L Wang,Y L Deng,L Rao,Z W Mao,R H Lei,H Qing

doi:10.1038/cddis.2013.412

H Ma, Z Y Yang + Show 6 more

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https://doi.org/10.1038/cddis.2013.412

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Abstract

Ionizing radiation (IR) is of clinical importance for glioblastoma therapy; however, the recurrence of glioma characterized by radiation resistance remains a therapeutic challenge. Research on irradiation-induced transcription in glioblastomas can contribute to the understanding of radioresistance mechanisms. In this study, by using the total mRNA sequencing (RNA-seq) analysis, we assayed the global gene expression in a human glioma cell line U251 MG at various time points after exposure to a growth arrest dose of γ-rays. We identified 1656 genes with obvious changes at the transcriptional level in response to irradiation, and these genes were dynamically enriched in various biological processes or pathways, including cell cycle arrest, DNA replication, DNA repair and apoptosis. Interestingly, the results showed that cell death was not induced even many proapoptotic molecules, including death receptor 5 (DR5) and caspases were activated after radiation. The RNA-seq data analysis further revealed that both proapoptosis and antiapoptosis genes were affected by irradiation. Namely, most proapoptosis genes were early continually responsive, whereas antiapoptosis genes were responsive at later stages. Moreover, HMGB1, HMGB2 and TOP2A involved in the positive regulation of DNA fragmentation during apoptosis showed early continual downregulation due to irradiation. Furthermore, targeting of the TRAIL/DR5 pathway after irradiation led to significant apoptotic cell death, accompanied by the recovered gene expression of HMGB1, HMGB2 and TOP2A. Taken together, these results revealed that inactivation of proapoptotic signaling molecules in the nucleus and late activation of antiapoptotic genes may contribute to the radioresistance of gliomas. Overall, this study provided novel insights into not only the underlying mechanisms of radioresistance in glioblastomas but also the screening of multiple targets for radiotherapy.

Highlights

Targeting of the DNA damage response (DDR) signaling network in gliomas was found to sensitize tumors to radiation therapy and reverse therapeutic resistance.[6]
Inhibition of PARP1, which is actively involved in the singlestranded DNA excision repair process, can disturb the cellular repair of radiation-induced ssDNA, and PARP1 inhibitors have been incorporated into radiation therapy for glioblastomas.[7]
As DR5 is known to be primarily expressed in malignant glioma cells,[41,42] we investigated whether combination treatment with tumor-related apoptosis-induced ligand (TRAIL), a DR5 ligand, and irradiation destroys the balance between pro- and antiapoptotic factors by activating the TRAIL/DR5 apoptotic pathway

Summary

Introduction

Targeting of the DDR signaling network in gliomas was found to sensitize tumors to radiation therapy and reverse therapeutic resistance.[6]. NF-kB, which transactivates its target genes, including cox-2, bcl-2, bcl-xL, XIAP and survivin,[12] and the expression of these antiapoptotic genes disrupts apoptosis signaling, thereby mediating radioresistance. Other mechanisms and pathways, including aberrant p21 regulation,[14] the Notch signaling pathway,[15] the Wnt pathway,[16] radiation-induced Akt activation,[17] as well as abnormal p53 function,[18] have been correlated with radioresistance in human glioblastoma cells. We focused on the apoptosis pathway activated by irradiation and investigated the significance of proapoptosis and antiapoptosis genes in glioblastoma radioresistance. Together, these should provide prime information for research on radiotherapy of glioblastomas

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Conclusion