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Transcriptional and post-transcriptional mechanisms for oncogenic overexpression of ether à go-go K+ channel.

Lin H, Li Z, Chen C, Luo X, Xiao J, Dong D, Lu Y, Yang B, Wang Z - PLoS ONE (2011)

Bottom Line: It was found to be necessary for cell cycle progression and tumorigenesis.H-eag1antisense antagonized the growth-stimulating effects and the upregulation of h-eag1 expression in SHSY5Y cells, induced by knockdown of miR-34, E2F1 overexpression, or inhibition of p53 activity.Moreover, these findings place h-eag1 in the p53-miR-34-E2F1-h-eag1 pathway with h-eag as a terminal effecter component and with miR-34 (and E2F1) as a linker between p53 and h-eag1.

View Article: PubMed Central - PubMed

Affiliation: Research Center, Montreal Heart Institute, Montreal, Quebec, Canada.

ABSTRACT
The human ether-à-go-go-1 (h-eag1) K(+) channel is expressed in a variety of cell lines derived from human malignant tumors and in clinical samples of several different cancers, but is otherwise absent in normal tissues. It was found to be necessary for cell cycle progression and tumorigenesis. Specific inhibition of h-eag1 expression leads to inhibition of tumor cell proliferation. We report here that h-eag1 expression is controlled by the p53-miR-34-E2F1 pathway through a negative feed-forward mechanism. We first established E2F1 as a transactivator of h-eag1 gene through characterizing its promoter region. We then revealed that miR-34, a known transcriptional target of p53, is an important negative regulator of h-eag1 through dual mechanisms by directly repressing h-eag1 at the post-transcriptional level and indirectly silencing h-eag1 at the transcriptional level via repressing E2F1. There is a strong inverse relationship between the expression levels of miR-34 and h-eag1 protein. H-eag1antisense antagonized the growth-stimulating effects and the upregulation of h-eag1 expression in SHSY5Y cells, induced by knockdown of miR-34, E2F1 overexpression, or inhibition of p53 activity. Therefore, p53 negatively regulates h-eag1 expression by a negative feed-forward mechanism through the p53-miR-34-E2F1 pathway. Inactivation of p53 activity, as is the case in many cancers, can thus cause oncogenic overexpression of h-eag1 by relieving the negative feed-forward regulation. These findings not only help us understand the molecular mechanisms for oncogenic overexpression of h-eag1 in tumorigenesis but also uncover the cell-cycle regulation through the p53-miR-34-E2F1-h-eag1 pathway. Moreover, these findings place h-eag1 in the p53-miR-34-E2F1-h-eag1 pathway with h-eag as a terminal effecter component and with miR-34 (and E2F1) as a linker between p53 and h-eag1. Our study therefore fills the gap between p53 pathway and its cellular function mediated by h-eag1.

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Related in: MedlinePlus

Effects of the p53−miR-34−E2F1−h-eag1 pathway on cell proliferation.(A & B) Effects of p53 activation by nutlin-3 (1 µM), E2F1 overexpression and miR-34 knockdown on SHSY5Y cell proliferation evaluated with MTT assay (A) and by population doubling time (PDT) with flow cytometry methods (B). Cells were pretreated with nutlin-3 to activate p53 and then transfected with the plasmid carrying E2F1 cDNA for overexpression (E2F1-P) or MT-AMO to knockdown miR-34; control cells (Ctl/Lipo) were mock-treated with lipofectamine 2000. *p<0.05 vs Ctl/Lipo; φp<0.05 vs Nutlin-3 alone; n = 4 for each group. (C & D) Effect of the antisense oligodeoxynucleotides (ASO) directed against h-eag gene on SHSY5Y cell growth induced by E2F1 overexpression, evaluated with MTT assay (C) and by PDT using flow cytometry methods (D). Cells were transfected with E2F1 plasmid alone (E2F1-P) or co-transfected with E2F1 plasmid and ASO (+ASO) or SO (sense oligomer for negative control; +SO). *p<0.05 vs Ctl/Lipo; φp<0.05 vs E2F1-P alone; n = 4 for each group. (E & F) Effects of antisense to h-eag1 (ASO) on cell-growth stimulation by PTF-α-induced p53 inactivation in SHSY5Y cells, determined by MTT (E) and by PDT (F). Cells were pretreated with PFT-α (30 µM) to inactivate p53 or transfected with MT-AMO, and then transfected with ASO; control cells (Ctl/Lipo) were mock-treated with lipofectamine 2000. *p<0.05 vs Ctl/Lipo; φp<0.05 vs PFT-α alone; n = 5 for each group.
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pone-0020362-g007: Effects of the p53−miR-34−E2F1−h-eag1 pathway on cell proliferation.(A & B) Effects of p53 activation by nutlin-3 (1 µM), E2F1 overexpression and miR-34 knockdown on SHSY5Y cell proliferation evaluated with MTT assay (A) and by population doubling time (PDT) with flow cytometry methods (B). Cells were pretreated with nutlin-3 to activate p53 and then transfected with the plasmid carrying E2F1 cDNA for overexpression (E2F1-P) or MT-AMO to knockdown miR-34; control cells (Ctl/Lipo) were mock-treated with lipofectamine 2000. *p<0.05 vs Ctl/Lipo; φp<0.05 vs Nutlin-3 alone; n = 4 for each group. (C & D) Effect of the antisense oligodeoxynucleotides (ASO) directed against h-eag gene on SHSY5Y cell growth induced by E2F1 overexpression, evaluated with MTT assay (C) and by PDT using flow cytometry methods (D). Cells were transfected with E2F1 plasmid alone (E2F1-P) or co-transfected with E2F1 plasmid and ASO (+ASO) or SO (sense oligomer for negative control; +SO). *p<0.05 vs Ctl/Lipo; φp<0.05 vs E2F1-P alone; n = 4 for each group. (E & F) Effects of antisense to h-eag1 (ASO) on cell-growth stimulation by PTF-α-induced p53 inactivation in SHSY5Y cells, determined by MTT (E) and by PDT (F). Cells were pretreated with PFT-α (30 µM) to inactivate p53 or transfected with MT-AMO, and then transfected with ASO; control cells (Ctl/Lipo) were mock-treated with lipofectamine 2000. *p<0.05 vs Ctl/Lipo; φp<0.05 vs PFT-α alone; n = 5 for each group.

Mentions: These above data allowed us to propose a new signaling pathway p53−miR-34−E2F1−h-eag1 (Fig. 6). Thus, we next sought to examine whether regulation of this pathway is related to the cell growth profile. We first demonstrated that activation of p53 by nutlin-3 induced a cell growth arrest in SHSY5Y cells, and overexpression of E2F1 alleviated the cell growth inhibition and so did transfection with the MT-AMO to knock down miR-34 (Fig. 7A & 7B). On the other hand, the direct growth-stimulating effect of E2F1 was remarkably attenuated by inhibition of h-eag1 with the antisense oligodeoxynucleotides directed against h-eag1 gene but not by the sense oligomer for negative control (Fig. 7C & 7D). Further, inactivation of p53 by PFT-α or MT-AMO promoted cell growth, which was abrogated by the antisense to h-eag1 (Fig. 7E & 7F).


Transcriptional and post-transcriptional mechanisms for oncogenic overexpression of ether à go-go K+ channel.

Lin H, Li Z, Chen C, Luo X, Xiao J, Dong D, Lu Y, Yang B, Wang Z - PLoS ONE (2011)

Effects of the p53−miR-34−E2F1−h-eag1 pathway on cell proliferation.(A & B) Effects of p53 activation by nutlin-3 (1 µM), E2F1 overexpression and miR-34 knockdown on SHSY5Y cell proliferation evaluated with MTT assay (A) and by population doubling time (PDT) with flow cytometry methods (B). Cells were pretreated with nutlin-3 to activate p53 and then transfected with the plasmid carrying E2F1 cDNA for overexpression (E2F1-P) or MT-AMO to knockdown miR-34; control cells (Ctl/Lipo) were mock-treated with lipofectamine 2000. *p<0.05 vs Ctl/Lipo; φp<0.05 vs Nutlin-3 alone; n = 4 for each group. (C & D) Effect of the antisense oligodeoxynucleotides (ASO) directed against h-eag gene on SHSY5Y cell growth induced by E2F1 overexpression, evaluated with MTT assay (C) and by PDT using flow cytometry methods (D). Cells were transfected with E2F1 plasmid alone (E2F1-P) or co-transfected with E2F1 plasmid and ASO (+ASO) or SO (sense oligomer for negative control; +SO). *p<0.05 vs Ctl/Lipo; φp<0.05 vs E2F1-P alone; n = 4 for each group. (E & F) Effects of antisense to h-eag1 (ASO) on cell-growth stimulation by PTF-α-induced p53 inactivation in SHSY5Y cells, determined by MTT (E) and by PDT (F). Cells were pretreated with PFT-α (30 µM) to inactivate p53 or transfected with MT-AMO, and then transfected with ASO; control cells (Ctl/Lipo) were mock-treated with lipofectamine 2000. *p<0.05 vs Ctl/Lipo; φp<0.05 vs PFT-α alone; n = 5 for each group.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3105031&req=5

pone-0020362-g007: Effects of the p53−miR-34−E2F1−h-eag1 pathway on cell proliferation.(A & B) Effects of p53 activation by nutlin-3 (1 µM), E2F1 overexpression and miR-34 knockdown on SHSY5Y cell proliferation evaluated with MTT assay (A) and by population doubling time (PDT) with flow cytometry methods (B). Cells were pretreated with nutlin-3 to activate p53 and then transfected with the plasmid carrying E2F1 cDNA for overexpression (E2F1-P) or MT-AMO to knockdown miR-34; control cells (Ctl/Lipo) were mock-treated with lipofectamine 2000. *p<0.05 vs Ctl/Lipo; φp<0.05 vs Nutlin-3 alone; n = 4 for each group. (C & D) Effect of the antisense oligodeoxynucleotides (ASO) directed against h-eag gene on SHSY5Y cell growth induced by E2F1 overexpression, evaluated with MTT assay (C) and by PDT using flow cytometry methods (D). Cells were transfected with E2F1 plasmid alone (E2F1-P) or co-transfected with E2F1 plasmid and ASO (+ASO) or SO (sense oligomer for negative control; +SO). *p<0.05 vs Ctl/Lipo; φp<0.05 vs E2F1-P alone; n = 4 for each group. (E & F) Effects of antisense to h-eag1 (ASO) on cell-growth stimulation by PTF-α-induced p53 inactivation in SHSY5Y cells, determined by MTT (E) and by PDT (F). Cells were pretreated with PFT-α (30 µM) to inactivate p53 or transfected with MT-AMO, and then transfected with ASO; control cells (Ctl/Lipo) were mock-treated with lipofectamine 2000. *p<0.05 vs Ctl/Lipo; φp<0.05 vs PFT-α alone; n = 5 for each group.
Mentions: These above data allowed us to propose a new signaling pathway p53−miR-34−E2F1−h-eag1 (Fig. 6). Thus, we next sought to examine whether regulation of this pathway is related to the cell growth profile. We first demonstrated that activation of p53 by nutlin-3 induced a cell growth arrest in SHSY5Y cells, and overexpression of E2F1 alleviated the cell growth inhibition and so did transfection with the MT-AMO to knock down miR-34 (Fig. 7A & 7B). On the other hand, the direct growth-stimulating effect of E2F1 was remarkably attenuated by inhibition of h-eag1 with the antisense oligodeoxynucleotides directed against h-eag1 gene but not by the sense oligomer for negative control (Fig. 7C & 7D). Further, inactivation of p53 by PFT-α or MT-AMO promoted cell growth, which was abrogated by the antisense to h-eag1 (Fig. 7E & 7F).

Bottom Line: It was found to be necessary for cell cycle progression and tumorigenesis.H-eag1antisense antagonized the growth-stimulating effects and the upregulation of h-eag1 expression in SHSY5Y cells, induced by knockdown of miR-34, E2F1 overexpression, or inhibition of p53 activity.Moreover, these findings place h-eag1 in the p53-miR-34-E2F1-h-eag1 pathway with h-eag as a terminal effecter component and with miR-34 (and E2F1) as a linker between p53 and h-eag1.

View Article: PubMed Central - PubMed

Affiliation: Research Center, Montreal Heart Institute, Montreal, Quebec, Canada.

ABSTRACT
The human ether-à-go-go-1 (h-eag1) K(+) channel is expressed in a variety of cell lines derived from human malignant tumors and in clinical samples of several different cancers, but is otherwise absent in normal tissues. It was found to be necessary for cell cycle progression and tumorigenesis. Specific inhibition of h-eag1 expression leads to inhibition of tumor cell proliferation. We report here that h-eag1 expression is controlled by the p53-miR-34-E2F1 pathway through a negative feed-forward mechanism. We first established E2F1 as a transactivator of h-eag1 gene through characterizing its promoter region. We then revealed that miR-34, a known transcriptional target of p53, is an important negative regulator of h-eag1 through dual mechanisms by directly repressing h-eag1 at the post-transcriptional level and indirectly silencing h-eag1 at the transcriptional level via repressing E2F1. There is a strong inverse relationship between the expression levels of miR-34 and h-eag1 protein. H-eag1antisense antagonized the growth-stimulating effects and the upregulation of h-eag1 expression in SHSY5Y cells, induced by knockdown of miR-34, E2F1 overexpression, or inhibition of p53 activity. Therefore, p53 negatively regulates h-eag1 expression by a negative feed-forward mechanism through the p53-miR-34-E2F1 pathway. Inactivation of p53 activity, as is the case in many cancers, can thus cause oncogenic overexpression of h-eag1 by relieving the negative feed-forward regulation. These findings not only help us understand the molecular mechanisms for oncogenic overexpression of h-eag1 in tumorigenesis but also uncover the cell-cycle regulation through the p53-miR-34-E2F1-h-eag1 pathway. Moreover, these findings place h-eag1 in the p53-miR-34-E2F1-h-eag1 pathway with h-eag as a terminal effecter component and with miR-34 (and E2F1) as a linker between p53 and h-eag1. Our study therefore fills the gap between p53 pathway and its cellular function mediated by h-eag1.

Show MeSH
Related in: MedlinePlus