siRNA Down-regulation of the PATZ1 Gene in Human Glioma Cells Increases Their Sensitivity to Apoptotic Stimuli

The PATZ1 gene encodes a transcription factor that belongs to the BTB/POZ group of transcriptional regulators and has been implicated as a transcriptional repressor. We cloned cDNA from glioma cell lines and found they expressed transcript variant 2 of PATZ1. We designed a specific siRNA against PATZ1 and showed that this siRNA, but not a control randomized siRNA, reduced PATZ1 expression in glioma cells as determined by quantitative PCR. In a panel of human glioma cell lines incubated with proapoptotic FasL, those transfected with PATZ1 siRNA displayed reduced cell numbers by the MTT colorimetric assay, relative to those transfected with randomized siRNA. Further studies showed that in 10-08-MG, U-251MG, U-87MG, and T98G cells PATZ1 siRNA significantly increased apoptosis in response to incubation with soluble FasL, as shown by a morphologic acridine orange/ethidium bromide apoptotic assay. Using an apoptosis specific cDNA microarray we further demonstrated that down-regulation of PATZ1 by siRNA resulted in the upregulation of death receptor pro-apoptotic genes including caspase 8 and Death Receptor 5 (DR5) in U-373MG cells. Since DR5 is the receptor for TRAIL we tested whether PATZ1 downregulation also sensitized cells to TRAIL-induced apoptosis and found that PATZ1 siRNA, but not control siRNA, sensitized U-251MG and T98G glioma cells to TRAIL-induced apoptosis. Altogether, these data demonstrate a previously unknown role for the transcription factor PATZ1 in conferring resistance to apoptosis and indicate that modulation of PATZ1 expression may be a therapeutic strategy for gliomas.