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Human cytomegalovirus inhibits apoptosis by regulating the activating transcription factor 5 signaling pathway in human malignant glioma cells.

Wang T, Qian D, Hu M, Li L, Zhang L, Chen H, Yang R, Wang B - Oncol Lett (2014)

Bottom Line: Furthermore, in glioblastoma U87 cells, HCMV infection induced cellular proliferation in parallel with an increase in the expression level of ATF5 and B-cell lymphoma/leukemia-2 to Bcl-2-associated X protein ratio.Loss of ATF5 function was achieved using a dominant-negative form of ATF5 in U87 cells, whereby cells appeared to grow marginally following HCMV infection when compared with the control.These results indicate that ATF5 signaling pathways may be important in the anti-apoptotic activity of HCMV-infected glioblastoma cells; therefore, the anti-apoptotic molecular mechanisms of HCMV in human glioblastoma cells were investigated in the current study.

View Article: PubMed Central - PubMed

Affiliation: Department of Microbiology, Qingdao University Medical College, Qingdao, Shandong 266071, P.R. China.

ABSTRACT
The activating transcription factor 5 (ATF5), also termed ATFx, is a member of the ATF/cAMP response element-binding protein (CREB) family of basic zipper proteins. ATF5 is an anti-apoptotic protein that is highly expressed in malignant glioma and is essential for glioma cell survival. Accumulating evidence indicates that human malignant gliomas are universally infected with human cytomegalovirus (HCMV). Recent studies have shown that HCMV may be resistant to the induction of apoptosis by disrupting cellular pathways in glioblastoma. To investigate the potential anti-apoptotic function of HCMV in glioma, malignant U87 glioma cells were infected with HCMV. The present study showed that HCMV infection suppressed apoptosis in glioblastoma U87 cells by regulating the expression of ATF5. Furthermore, in glioblastoma U87 cells, HCMV infection induced cellular proliferation in parallel with an increase in the expression level of ATF5 and B-cell lymphoma/leukemia-2 to Bcl-2-associated X protein ratio. Loss of ATF5 function was achieved using a dominant-negative form of ATF5 in U87 cells, whereby cells appeared to grow marginally following HCMV infection when compared with the control. However, the anti-apoptotic ability was appeared to decline in the terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling assay. These results indicate that ATF5 signaling pathways may be important in the anti-apoptotic activity of HCMV-infected glioblastoma cells; therefore, the anti-apoptotic molecular mechanisms of HCMV in human glioblastoma cells were investigated in the current study. Prevention of HCMV infection may present a potential and promising approach for the treatment of malignant gliomas.

No MeSH data available.


Related in: MedlinePlus

Apoptotic analysis of U87 cells exhibiting a loss of ATF5 function and treatment with or without HCMV by TUNEL assay and hematoxylin staining. (A) U87 cells and (B) HCMV-infected U87 cells did not demonstrate apoptosis. (C) Interfering with ATF5 function resulted in U87 cell apoptosis (as shown by arrows) and this data was consistent with previous studies (31). (D) U87 cells were transfected with pLeGFP-C1 plasmids using Lipofectamine 2000. A significant decrease was observed in (E) HCMV-infected control and TUNEL-positive cells. (C) U87 cells were transfected with the pLeGFP-C1-NTAzip-ATF5 plasmid and apoptosis was evident. (F) HCMV-infected U87 cells with ATF5 loss of function exhibited a decrease in TUNEL-positive cells. Magnification, 400. (G) Bar chart showing the mean apoptosis index per slide (A-F;*P<0.05). ATF5, activating transcription factor 5; HMCV, human cytomegalovirus; dn, dominant-negative; TUNEL, terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling.
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f3-ol-08-03-1051: Apoptotic analysis of U87 cells exhibiting a loss of ATF5 function and treatment with or without HCMV by TUNEL assay and hematoxylin staining. (A) U87 cells and (B) HCMV-infected U87 cells did not demonstrate apoptosis. (C) Interfering with ATF5 function resulted in U87 cell apoptosis (as shown by arrows) and this data was consistent with previous studies (31). (D) U87 cells were transfected with pLeGFP-C1 plasmids using Lipofectamine 2000. A significant decrease was observed in (E) HCMV-infected control and TUNEL-positive cells. (C) U87 cells were transfected with the pLeGFP-C1-NTAzip-ATF5 plasmid and apoptosis was evident. (F) HCMV-infected U87 cells with ATF5 loss of function exhibited a decrease in TUNEL-positive cells. Magnification, 400. (G) Bar chart showing the mean apoptosis index per slide (A-F;*P<0.05). ATF5, activating transcription factor 5; HMCV, human cytomegalovirus; dn, dominant-negative; TUNEL, terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling.

Mentions: Previous studies have demonstrated that HCMV may increase the malignancy of glioma by blocking apoptosis. ATF5 is closely associated with tumor cell apoptosis. In addition, the present study found that HCMV infection regulates the expression of ATF5 in glioma. It is hypothesized that anti-apoptosis of HCMV infection may be associated with ATF5 pathways. In siATF5 U87 cells, almost no apoptotic cells were identified. However, apoptosis occurred in U87 cells, which were transfected with dnATF5 plasmids. Furthermore, apoptotic cell death was detected in ~40% of dnATF5 U87 cells. The number of TUNEL-positive cells (dead cells) decreased by 4–5% following HCMV infection. As shown in Fig. 3, TUNEL-positive cells were not observed in normal or U87 cells (Fig. 3A and B), however, TUNEL-positive cells were detected in dnATF5 U87 cells (Fig. 3C). Following HCMV infection for 48 h, 40% of TUNEL-positive cells were detected in dnATF5 U87 cells whereas 35% of TUNEL-positive cells were detected in HCMV-infected dnATF5 cells (Fig. 3G). Compared with the control, in U87 cells, which had lost ATF5 function, no significant difference was identified in the decline of TUNEL-positive cells (Fig. 3G). These results support the hypothesis that the anti-apoptotic effect of HCMV infection is associated with ATF5 expression.


Human cytomegalovirus inhibits apoptosis by regulating the activating transcription factor 5 signaling pathway in human malignant glioma cells.

Wang T, Qian D, Hu M, Li L, Zhang L, Chen H, Yang R, Wang B - Oncol Lett (2014)

Apoptotic analysis of U87 cells exhibiting a loss of ATF5 function and treatment with or without HCMV by TUNEL assay and hematoxylin staining. (A) U87 cells and (B) HCMV-infected U87 cells did not demonstrate apoptosis. (C) Interfering with ATF5 function resulted in U87 cell apoptosis (as shown by arrows) and this data was consistent with previous studies (31). (D) U87 cells were transfected with pLeGFP-C1 plasmids using Lipofectamine 2000. A significant decrease was observed in (E) HCMV-infected control and TUNEL-positive cells. (C) U87 cells were transfected with the pLeGFP-C1-NTAzip-ATF5 plasmid and apoptosis was evident. (F) HCMV-infected U87 cells with ATF5 loss of function exhibited a decrease in TUNEL-positive cells. Magnification, 400. (G) Bar chart showing the mean apoptosis index per slide (A-F;*P<0.05). ATF5, activating transcription factor 5; HMCV, human cytomegalovirus; dn, dominant-negative; TUNEL, terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling.
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Related In: Results  -  Collection

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f3-ol-08-03-1051: Apoptotic analysis of U87 cells exhibiting a loss of ATF5 function and treatment with or without HCMV by TUNEL assay and hematoxylin staining. (A) U87 cells and (B) HCMV-infected U87 cells did not demonstrate apoptosis. (C) Interfering with ATF5 function resulted in U87 cell apoptosis (as shown by arrows) and this data was consistent with previous studies (31). (D) U87 cells were transfected with pLeGFP-C1 plasmids using Lipofectamine 2000. A significant decrease was observed in (E) HCMV-infected control and TUNEL-positive cells. (C) U87 cells were transfected with the pLeGFP-C1-NTAzip-ATF5 plasmid and apoptosis was evident. (F) HCMV-infected U87 cells with ATF5 loss of function exhibited a decrease in TUNEL-positive cells. Magnification, 400. (G) Bar chart showing the mean apoptosis index per slide (A-F;*P<0.05). ATF5, activating transcription factor 5; HMCV, human cytomegalovirus; dn, dominant-negative; TUNEL, terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling.
Mentions: Previous studies have demonstrated that HCMV may increase the malignancy of glioma by blocking apoptosis. ATF5 is closely associated with tumor cell apoptosis. In addition, the present study found that HCMV infection regulates the expression of ATF5 in glioma. It is hypothesized that anti-apoptosis of HCMV infection may be associated with ATF5 pathways. In siATF5 U87 cells, almost no apoptotic cells were identified. However, apoptosis occurred in U87 cells, which were transfected with dnATF5 plasmids. Furthermore, apoptotic cell death was detected in ~40% of dnATF5 U87 cells. The number of TUNEL-positive cells (dead cells) decreased by 4–5% following HCMV infection. As shown in Fig. 3, TUNEL-positive cells were not observed in normal or U87 cells (Fig. 3A and B), however, TUNEL-positive cells were detected in dnATF5 U87 cells (Fig. 3C). Following HCMV infection for 48 h, 40% of TUNEL-positive cells were detected in dnATF5 U87 cells whereas 35% of TUNEL-positive cells were detected in HCMV-infected dnATF5 cells (Fig. 3G). Compared with the control, in U87 cells, which had lost ATF5 function, no significant difference was identified in the decline of TUNEL-positive cells (Fig. 3G). These results support the hypothesis that the anti-apoptotic effect of HCMV infection is associated with ATF5 expression.

Bottom Line: Furthermore, in glioblastoma U87 cells, HCMV infection induced cellular proliferation in parallel with an increase in the expression level of ATF5 and B-cell lymphoma/leukemia-2 to Bcl-2-associated X protein ratio.Loss of ATF5 function was achieved using a dominant-negative form of ATF5 in U87 cells, whereby cells appeared to grow marginally following HCMV infection when compared with the control.These results indicate that ATF5 signaling pathways may be important in the anti-apoptotic activity of HCMV-infected glioblastoma cells; therefore, the anti-apoptotic molecular mechanisms of HCMV in human glioblastoma cells were investigated in the current study.

View Article: PubMed Central - PubMed

Affiliation: Department of Microbiology, Qingdao University Medical College, Qingdao, Shandong 266071, P.R. China.

ABSTRACT
The activating transcription factor 5 (ATF5), also termed ATFx, is a member of the ATF/cAMP response element-binding protein (CREB) family of basic zipper proteins. ATF5 is an anti-apoptotic protein that is highly expressed in malignant glioma and is essential for glioma cell survival. Accumulating evidence indicates that human malignant gliomas are universally infected with human cytomegalovirus (HCMV). Recent studies have shown that HCMV may be resistant to the induction of apoptosis by disrupting cellular pathways in glioblastoma. To investigate the potential anti-apoptotic function of HCMV in glioma, malignant U87 glioma cells were infected with HCMV. The present study showed that HCMV infection suppressed apoptosis in glioblastoma U87 cells by regulating the expression of ATF5. Furthermore, in glioblastoma U87 cells, HCMV infection induced cellular proliferation in parallel with an increase in the expression level of ATF5 and B-cell lymphoma/leukemia-2 to Bcl-2-associated X protein ratio. Loss of ATF5 function was achieved using a dominant-negative form of ATF5 in U87 cells, whereby cells appeared to grow marginally following HCMV infection when compared with the control. However, the anti-apoptotic ability was appeared to decline in the terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling assay. These results indicate that ATF5 signaling pathways may be important in the anti-apoptotic activity of HCMV-infected glioblastoma cells; therefore, the anti-apoptotic molecular mechanisms of HCMV in human glioblastoma cells were investigated in the current study. Prevention of HCMV infection may present a potential and promising approach for the treatment of malignant gliomas.

No MeSH data available.


Related in: MedlinePlus