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Interplay between REST and nucleolin transcription factors: a key mechanism in the overexpression of genes upon increased phosphorylation.

Tediose T, Kolev M, Sivasankar B, Brennan P, Morgan BP, Donev R - Nucleic Acids Res. (2010)

Bottom Line: Here, we identify a mechanism that contributes to the activation of genes, expression of which is controlled by responsive elements containing overlapping binding sites for REST and nucleolin.We demonstrate that both phosphorylated and non-phosphorylated nucleolin-bound DNA; however, only phosphorylated nucleolin successfully competed with either full-length REST or a REST-derived DNA-binding peptide, REST68, for binding to the overlapping binding sites.We show that this interplay between the two transcription factors regulates the activation of cell survival and immunomodulatory genes in tumors and non-malignant cells with activated protein kinase C, which is accompanied with alterations in cell proliferation and apoptosis.

View Article: PubMed Central - PubMed

Affiliation: Department of Infection, Immunity and Biochemistry, School of Medicine, Cardiff University, Cardiff CF14 4XN, UK.

ABSTRACT
Non-malignant cells can be transformed via the activation of kinases that control degradation of neural-restrictive silencer factor (REST). Here, we identify a mechanism that contributes to the activation of genes, expression of which is controlled by responsive elements containing overlapping binding sites for REST and nucleolin. We demonstrate that both phosphorylated and non-phosphorylated nucleolin-bound DNA; however, only phosphorylated nucleolin successfully competed with either full-length REST or a REST-derived DNA-binding peptide, REST68, for binding to the overlapping binding sites. We show that this interplay between the two transcription factors regulates the activation of cell survival and immunomodulatory genes in tumors and non-malignant cells with activated protein kinase C, which is accompanied with alterations in cell proliferation and apoptosis. We propose a model for the regulation of these genes, which brings a new insight into the molecular mechanisms that control cellular transformation driven by activation of protein kinases.

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A model for regulation of genes with overlapping REST/NCL binding sites. (A) In malignant cells, protein kinases such as PI3 and PKC are activated resulting in degradation of the full-length REST that binds to a responsive element within the promoter of the gene and in phosphorylation of NCL, which together leads to a displacement of the remaining REST from the gene promoter and high expression levels. Treatment of such tumors with the REST68 peptide (degradation is not affected by phosphorylation) suppresses expression of the gene by competing with phosphorylated NCL. However, if cells are treated further with inhibitors of NCL phosphorylation, NCL will no longer be in competition for binding and gene expression will be suppressed further. (B) The model is similar to the one shown in (A); however, tumor types like colon carcinoma, neuroblastoma and small-cell lung carcinoma lack REST that can bind to DNA and suppress gene expression. In these tumors, both phosphorylated and non-phosphorylated NCL can bind to the gene promoter and activate expression. REST68 treatment prevents non-phosphorylated NCL from binding to the REST/NCL overlapping binding sites, partially decreasing the expression. Hence, further treatment with kinase inhibitors does not allow for competition between REST68 and NCL, resulting in even stronger inhibition of the controlled gene.
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Figure 8: A model for regulation of genes with overlapping REST/NCL binding sites. (A) In malignant cells, protein kinases such as PI3 and PKC are activated resulting in degradation of the full-length REST that binds to a responsive element within the promoter of the gene and in phosphorylation of NCL, which together leads to a displacement of the remaining REST from the gene promoter and high expression levels. Treatment of such tumors with the REST68 peptide (degradation is not affected by phosphorylation) suppresses expression of the gene by competing with phosphorylated NCL. However, if cells are treated further with inhibitors of NCL phosphorylation, NCL will no longer be in competition for binding and gene expression will be suppressed further. (B) The model is similar to the one shown in (A); however, tumor types like colon carcinoma, neuroblastoma and small-cell lung carcinoma lack REST that can bind to DNA and suppress gene expression. In these tumors, both phosphorylated and non-phosphorylated NCL can bind to the gene promoter and activate expression. REST68 treatment prevents non-phosphorylated NCL from binding to the REST/NCL overlapping binding sites, partially decreasing the expression. Hence, further treatment with kinase inhibitors does not allow for competition between REST68 and NCL, resulting in even stronger inhibition of the controlled gene.

Mentions: The above results, together with our previously published data, enabled us to propose a model for the upregulation of expression of genes with overlapping REST/NCL binding sites in their promoters upon activation of protein kinases (Figure 8). In non-malignant cells, REST is expressed at a relatively high level, and NCL phosphorylation is moderate compared to transformed cells. Thus, REST is bound to the gene promoters. However, upon activation of kinases like PKCξ, p34cdc2 and PI3K, which occurs in cellular transformation (1,5,38), NCL is phosphorylated and the half-life of REST decreases as a consequence of its increased degradation (12). These events cause decreased binding of REST and increased binding of NCL to the overlapping binding sites in the gene promoter (Figure 8A). Treatment of such tumors with the REST68 peptide, degradation of which is not affected by phosphorylation, suppresses expression of the gene by competing with phosphorylated nucleolin. However, if cells are treated further with inhibitors of the protein kinases that use NCL as a substrate, the amount of endogenous REST increases which together with the REST68 peptide and inhibited phosphorylation of NCL results in additional inhibition of gene expression.Figure 8.


Interplay between REST and nucleolin transcription factors: a key mechanism in the overexpression of genes upon increased phosphorylation.

Tediose T, Kolev M, Sivasankar B, Brennan P, Morgan BP, Donev R - Nucleic Acids Res. (2010)

A model for regulation of genes with overlapping REST/NCL binding sites. (A) In malignant cells, protein kinases such as PI3 and PKC are activated resulting in degradation of the full-length REST that binds to a responsive element within the promoter of the gene and in phosphorylation of NCL, which together leads to a displacement of the remaining REST from the gene promoter and high expression levels. Treatment of such tumors with the REST68 peptide (degradation is not affected by phosphorylation) suppresses expression of the gene by competing with phosphorylated NCL. However, if cells are treated further with inhibitors of NCL phosphorylation, NCL will no longer be in competition for binding and gene expression will be suppressed further. (B) The model is similar to the one shown in (A); however, tumor types like colon carcinoma, neuroblastoma and small-cell lung carcinoma lack REST that can bind to DNA and suppress gene expression. In these tumors, both phosphorylated and non-phosphorylated NCL can bind to the gene promoter and activate expression. REST68 treatment prevents non-phosphorylated NCL from binding to the REST/NCL overlapping binding sites, partially decreasing the expression. Hence, further treatment with kinase inhibitors does not allow for competition between REST68 and NCL, resulting in even stronger inhibition of the controlled gene.
© Copyright Policy - creative-commons
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2875004&req=5

Figure 8: A model for regulation of genes with overlapping REST/NCL binding sites. (A) In malignant cells, protein kinases such as PI3 and PKC are activated resulting in degradation of the full-length REST that binds to a responsive element within the promoter of the gene and in phosphorylation of NCL, which together leads to a displacement of the remaining REST from the gene promoter and high expression levels. Treatment of such tumors with the REST68 peptide (degradation is not affected by phosphorylation) suppresses expression of the gene by competing with phosphorylated NCL. However, if cells are treated further with inhibitors of NCL phosphorylation, NCL will no longer be in competition for binding and gene expression will be suppressed further. (B) The model is similar to the one shown in (A); however, tumor types like colon carcinoma, neuroblastoma and small-cell lung carcinoma lack REST that can bind to DNA and suppress gene expression. In these tumors, both phosphorylated and non-phosphorylated NCL can bind to the gene promoter and activate expression. REST68 treatment prevents non-phosphorylated NCL from binding to the REST/NCL overlapping binding sites, partially decreasing the expression. Hence, further treatment with kinase inhibitors does not allow for competition between REST68 and NCL, resulting in even stronger inhibition of the controlled gene.
Mentions: The above results, together with our previously published data, enabled us to propose a model for the upregulation of expression of genes with overlapping REST/NCL binding sites in their promoters upon activation of protein kinases (Figure 8). In non-malignant cells, REST is expressed at a relatively high level, and NCL phosphorylation is moderate compared to transformed cells. Thus, REST is bound to the gene promoters. However, upon activation of kinases like PKCξ, p34cdc2 and PI3K, which occurs in cellular transformation (1,5,38), NCL is phosphorylated and the half-life of REST decreases as a consequence of its increased degradation (12). These events cause decreased binding of REST and increased binding of NCL to the overlapping binding sites in the gene promoter (Figure 8A). Treatment of such tumors with the REST68 peptide, degradation of which is not affected by phosphorylation, suppresses expression of the gene by competing with phosphorylated nucleolin. However, if cells are treated further with inhibitors of the protein kinases that use NCL as a substrate, the amount of endogenous REST increases which together with the REST68 peptide and inhibited phosphorylation of NCL results in additional inhibition of gene expression.Figure 8.

Bottom Line: Here, we identify a mechanism that contributes to the activation of genes, expression of which is controlled by responsive elements containing overlapping binding sites for REST and nucleolin.We demonstrate that both phosphorylated and non-phosphorylated nucleolin-bound DNA; however, only phosphorylated nucleolin successfully competed with either full-length REST or a REST-derived DNA-binding peptide, REST68, for binding to the overlapping binding sites.We show that this interplay between the two transcription factors regulates the activation of cell survival and immunomodulatory genes in tumors and non-malignant cells with activated protein kinase C, which is accompanied with alterations in cell proliferation and apoptosis.

View Article: PubMed Central - PubMed

Affiliation: Department of Infection, Immunity and Biochemistry, School of Medicine, Cardiff University, Cardiff CF14 4XN, UK.

ABSTRACT
Non-malignant cells can be transformed via the activation of kinases that control degradation of neural-restrictive silencer factor (REST). Here, we identify a mechanism that contributes to the activation of genes, expression of which is controlled by responsive elements containing overlapping binding sites for REST and nucleolin. We demonstrate that both phosphorylated and non-phosphorylated nucleolin-bound DNA; however, only phosphorylated nucleolin successfully competed with either full-length REST or a REST-derived DNA-binding peptide, REST68, for binding to the overlapping binding sites. We show that this interplay between the two transcription factors regulates the activation of cell survival and immunomodulatory genes in tumors and non-malignant cells with activated protein kinase C, which is accompanied with alterations in cell proliferation and apoptosis. We propose a model for the regulation of these genes, which brings a new insight into the molecular mechanisms that control cellular transformation driven by activation of protein kinases.

Show MeSH
Related in: MedlinePlus