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Tumor suppressor PDCD4 inhibits NF-?B-dependent transcription in human glioblastoma cells by direct interaction with p65.

ABSTRACT: PDCD4 is a tumor suppressor induced by apoptotic stimuli that regulates both translation and transcription. Previously, we showed that overexpression of PDCD4 leads to decreased anchorage-independent growth in glioblastoma (GBM)-derived cell lines and decreased tumor growth in a GBM xenograft model. In inflammatory cells, PDCD4 stimulates tumor necrosis factor-induced activation of the transcription factor NF-?B, an oncogenic driver in many cancer sites. However, the effect of PDCD4 on NF-?B transcriptional activity in most cancers including GBM is still unknown. We studied the effect of PDCD4 on NF-?B-dependent transcriptional activity in GBM by stably overexpressing PDCD4 in U251 and LN229 cells. Stable PDCD4 expression inhibits NF-?B transcriptional activation measured by a luciferase reporter. The molecular mechanism by which PDCD4 inhibits NF-?B transcriptional activation does not involve inhibited expression of NF-?B p65 or p50 proteins. PDCD4 does not inhibit pathways upstream of NF-?B including the activation of IKK? and IKK? kinases or degradation of I?B?, events needed for nuclear transport of p65 and p50. PDCD4 overexpression does inhibit localization of p65 but not p50 in the nucleus. PDCD4 protein interacts preferentially with p65 protein as shown by co-immunoprecipitation and confocal imaging. PDCD4 overexpression inhibits the mRNA expression of two NF-?B target genes in a p65-dependent manner. These results suggest that PDCD4 can significantly inhibit NF-?B activity in GBM cells by a mechanism that involves direct or indirect protein-protein interaction independent of the expected mRNA-selective translational inhibition. These findings offer novel opportunities for NF-?B-targeted interventions to prevent or treat cancer.

SUBMITTER: Hwang SK

PROVIDER: S-EPMC4076808 | biostudies-other | 2014 Jul

REPOSITORIES: biostudies-other

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Tumor suppressor PDCD4 inhibits NF-κB-dependent transcription in human glioblastoma cells by direct interaction with p65.

Hwang Soon-Kyung SK Baker Alyson R AR Young Matthew R MR Colburn Nancy H NH

Carcinogenesis 20140111 7

PDCD4 is a tumor suppressor induced by apoptotic stimuli that regulates both translation and transcription. Previously, we showed that overexpression of PDCD4 leads to decreased anchorage-independent growth in glioblastoma (GBM)-derived cell lines and decreased tumor growth in a GBM xenograft model. In inflammatory cells, PDCD4 stimulates tumor necrosis factor-induced activation of the transcription factor NF-κB, an oncogenic driver in many cancer sites. However, the effect of PDCD4 on NF-κB tra ...[more]

PMID: 24413684

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Project description:IntroductionNovel plant DING proteins (full-length 38 kDa p38SJ, and 27 kDa p27SJ) exhibit phosphatase activity and modulate HIV-1 gene transcription. Previously, we demonstrated that DING regulates HIV-1 gene transcription by dephosphorylation and inactivation of CTD RNA polymerase II, the major elongating factor of HIV-1 Long Terminal Repeats (LTR). Because the transcription of HIV-1 is controlled by several viral and cellular factors, including p65/p50 subunits of NF-κB, we hypothesized that DING phosphatase can also affect the phosphorylation and activity of p65 NF-κB, in addition to C-terminal Domain (CTD) of RNA Polymerase II (RNAPII), to suppress HIV-1 gene transcription and inhibit HIV-1 infection.MethodsHere, we describe the inhibition of HIV-1 infection and the p65/p50 NF-κB phosphorylation by DING protein, analyzed by ELISA and northern-blot assays, western-blot assays, cell fractionation, and promoter-reporter assays in DING-expressing cells, using a pTet-on inducible system.ResultsResults from HIV-1 infection assays demonstrate a strong inhibition of HIV-1 and HIV-LTR RNA expression by DING protein, determined by p24 ELISA and by northern blot assay. Results from the western blot assays and cell fractionation assays show that there is an increase in the level of hypo-phosphorylated form of p65 NF-κB in DING-expressing cells. Both fractions of p65/p50, nuclear or cytoplasmic, are affected by DING phosphatase, but more cytoplasmic accumulation of p65 NF-κB was found in the presence of DING, suggesting that subsequent activation and nuclear import of active NF-κB is affected by DING. The major portion of nuclear p65 was dephosphorylated in DING-expressing cells. The promoter-reporter assay demonstrated that DING-mediated dephosphorylation and dysregulation of NF-κB p65 lead to the suppression of its binding to HIV-1 LTR, and resulted in the inhibition of p65-mediated activation of LTR transcription. Mapping of the region within LTR that was affected by DING revealed that both, NF-κB and CTD RNA Polymerase II binding sites were important, and cooperativity of these cellular factors was diminished by DING. In addition, mapping of the region within DING-p38SJ that affected LTR transcription, revealed that phosphate-binding domain is essential for this inhibitory activity.ConclusionWe have demonstrated the effect of DING phosphatases on HIV-1 infection, phosphorylation of p65 NF-κB, and transcription of HIV-1 LTR. Our studies suggest that one possible mechanism by which DING can regulate the expression of HIV-1 LTR can be through dysregulation of the transcription factor NF-κB p65 by preventing its phosphorylation and translocation to the nucleus and binding to the HIV-1 LTR, an action that could contribute to the utility of DING p38SJ as an antiviral agent. Importantly, DING not only inhibits HIV-1 LTR gene transcription in the presence of increased p65 NF-κB, but also suppresses HIV-1 infection. DING protein improved inhibitory effects of the known anti-retroviral drugs, Tenofovir (TFV) and Emtricitabine (FTS) on HIV-1, since in the combination with these drugs; the suppression of HIV-1 by DNG was significantly higher when it was in combination with these drugs, compared to controls or cases without DING. Thus, our data support the use of neuroprotective DING proteins as novel therapeutic antiviral drugs that suppress HIV-1 LTR transcription by interfering with the function of NF-κB.

Dataset Information

Tumor suppressor PDCD4 inhibits NF-?B-dependent transcription in human glioblastoma cells by direct interaction with p65.

Publications

Tumor suppressor PDCD4 inhibits NF-κB-dependent transcription in human glioblastoma cells by direct interaction with p65.

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