Aims: The incidence of recurrent gliomas is high, exerting low survival rates and poor prognoses. Transcription factor AP-2α has been reported to regulate the progression of primary glioblastoma (GBM). However, the function of AP-2α in recurrent gliomas is largely unclear.
Methods: The expression of AP-2α and O6-methylguanine DNA-methyltransferase (MGMT) was detected in recurrent glioma tissues and cell lines by Western blots, the regulation mechanisms between AP-2α/MGMT promoter and RA/AP-2α promoter were studied by luciferase reporter assays, EMSA, and chIP assays. The effects of AP-2α and TMZ/RA treatment on cell viability in vitro and in vivo were investigated by MTT assays, γH2AX staining, comet assays and intracranial injection.
Key findings: AP-2α expression negatively correlates with the expression of MGMT in glioma samples. AP-2α could directly bind with the promoter of the MGMT gene, suppresses transcriptional levels of MGMT and downregulate MGMT expression in TMZ-resistant U87MG-R and T98G cells, but TMZ treatment decreases AP-2α expression and increases MGMT expression. The extended TMZ treatment and increased TMZ concentrations reversed these effects. Moreover, AP-2α overexpression combines with TMZ to decrease cell viability, concurrently with improved DNA damage marker γH2AX. Furthermore, retinoic acid (RA) activates RAR/RXR heterodimers, which bind to RA-responsive elements (RAREs) of the AP-2α promoter, and activates AP-2α expression in recurrent glioma cells. Finally, in intracranial relapsed glioma mouse model, both RA and TMZ could retard tumor development and prolong the mouse survival.
Significance: AP-2α activation by gene overexpression or RA treatment reveals the suppressive effects on glioma relapse, providing a novel therapeutic strategy against malignant refractory gliomas.
Keywords: AP-2α; DNA damage; Glioma recurrence; MGMT.
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