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Published on: August 25, 2021
TCEAL7, a putative tumor suppressor gene, negatively regulates NF-kappaB pathway
1Department of Experimental Pathology, Mayo Clinic College of Medicine, Rochester, MN, USA.
Abstract:
We have previously shown that a frequently downregulated gene, transcription elongation factor A-like 7 (TCEAL7), promoted anchorage-independent growth and modulated Myc activity in ovarian surface epithelial cells immortalized with temperature-sensitive large T antigen and human telomerase reverse transcriptase (OSEtsT/hTERT). Analysis of protein/DNA array showed that TCEAL7 downregulation resulted in an approximately twofold increase in nuclear factor (NF)-kappaB binding to its target DNA sequence. In this study we showed that short hairpin RNA (shRNA)-mediated downregulation of TCEAL7 in two different immortalized OSE cells showed higher NF-kappaB activity, as determined using reporter and gel-shift assays. Transient transfection of TCEAL7 inhibited the activation of NF-kappaB in TCEAL7-downregulated clones, IOSE-523 and in other ovarian cancer cell lines (OVCAR8, SKOV3ip and DOV13), suggesting that TCEAL7 negatively regulates NF-kappaB pathway. Consistent with this observation, TCEAL7-downregulated clones showed higher levels of NF-kappaB targets, such as pro-proliferative (cyclin-D1 and cMyc), pro-angiogenic (interleukin (IL)-6, IL-8 and vascular endothelial growth factor (VEGF)), inflammatory (intercellular adhesion molecule 1 (ICAM-1) and cyclooxygenase-2 (Cox-2)) and anti-apoptotic (B-cell lymphoma-extra large (Bcl-xl)) genes when compared with vector controls. Inhibition of NF-kappaB by IkappaB kinase (IKK) inhibitor (BMS 345541) attenuated cell survival and proliferation of TCEAL-knockdown clones. Although TCEAL7 inhibited p65 transcriptional activity, it did not modulate the cytoplasmic signaling of the NF-kappaB pathway, by itself or by tumor necrosis factor-alpha (TNF-alpha). Chromatin immunoprecipitation (ChIP) assays revealed increased recruitment of p65 and p300 to the promoters of IL-8 and IL-6 in TCEAL7-downregulated clones. Collectively, these results indicate a novel role for TCEAL7 in the negative regulation of NF-kappaB signaling at the basal level by modulating transcriptional activity of NF-kappaB on its target gene promoters, potentially providing a novel mechanism by which NF-kappaB activity may be deregulated in ovarian cancer cells.
Insights
Transcription elongation factor A-like 7 (TCEAL7) negatively regulates nuclear factor-kappaB (NF-κB) signaling in ovarian cells. Downregulation of TCEAL7 increases NF-κB activity, promoting cancer cell proliferation and survival.
Area of Science:
- Molecular Biology
- Cancer Biology
- Cell Signaling
Background:
- Transcription elongation factor A-like 7 (TCEAL7) is a frequently downregulated gene in ovarian cancer.
- Previous studies indicated TCEAL7 promotes anchorage-independent growth and modulates Myc activity.
Purpose of the Study:
- To investigate the role of TCEAL7 in regulating nuclear factor-kappaB (NF-κB) signaling pathway.
- To elucidate the mechanism by which TCEAL7 influences NF-κB activity in ovarian cancer cells.
Main Methods:
- Short hairpin RNA (shRNA)-mediated knockdown of TCEAL7 in immortalized ovarian surface epithelial (OSE) cells.
- Reporter assays, gel-shift assays, and transient transfection to assess NF-κB activity.
- Analysis of NF-κB target gene expression, including pro-proliferative, pro-angiogenic, inflammatory, and anti-apoptotic genes.
- Inhibition of NF-κB pathway using IκB kinase (IKK) inhibitor (BMS 345541).
- Chromatin immunoprecipitation (ChIP) assays to evaluate protein recruitment to gene promoters.
Main Results:
- TCEAL7 downregulation led to increased NF-κB binding and activity in OSE cells and ovarian cancer cell lines.
- Overexpression of TCEAL7 inhibited NF-κB activation in TCEAL7-downregulated cells.
- TCEAL7-knockdown cells exhibited elevated expression of NF-κB target genes involved in proliferation, angiogenesis, inflammation, and apoptosis.
- Inhibition of NF-κB attenuated the survival and proliferation of TCEAL7-knockdown cells.
- ChIP assays showed increased recruitment of p65 and p300 to IL-8 and IL-6 promoters in TCEAL7-downregulated cells.
Conclusions:
- TCEAL7 negatively regulates the NF-κB signaling pathway at the transcriptional level.
- TCEAL7 modulates the transcriptional activity of NF-κB on its target gene promoters.
- Dysregulation of TCEAL7 may contribute to elevated NF-κB activity in ovarian cancer, providing a novel mechanism for cancer progression.
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