Tristetraprolin regulates expression of VEGF and tumorigenesis in human colon cancer

Department of Biological Sciences, University of Ulsan, Ulsan 682-060, Korea.
International Journal of Cancer (Impact Factor: 5.09). 01/2009; 126(8):1817-27. DOI: 10.1002/ijc.24847
Source: PubMed


Tristetraprolin (TTP) is an AU-rich element-binding protein that regulates mRNA stability. Here, we report that TTP suppress the growth of human colon cancer cells both in vivo and in vitro by regulating of the expression of vascular endothelial growth factor (VEGF). TTP protein expression in human colonic tissues was markedly decreased in colonic adenocarcinoma compared with in normal mucosa and adenoma. VEGF expression was higher in colonic adenocarcinoma than in normal mucosa and adenoma. Specific inhibition of TTP expression by RNA-interference increased the expression of VEGF in cultured human colon cancer cells, and TTP overexpression markedly decreased it. In addition, elevated expression of TTP decreased the expression level of luciferase linked to a 3' terminal AU-rich element (ARE) of VEGF mRNA. Colo320/TTP cells overexpressing TTP grew slowly in vitro and became tumors small in size when xenografted s.c into nude mice. These findings demonstrate that TTP acts as a negative regulator of VEGF gene expression in colon cancer cells, suggesting that it can be used as novel therapeutic agent to treat colon cancer.

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Available from: Young Joo Min, Dec 23, 2014
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    • "Reduction in TTP compared to normal tissues has been observed in a number of tumours, including thyroid, lung, ovary, uterus, cervix, brain, head and neck and breast 17,33–35. We previously found that TTP restoration in MDA-MB-231 cells promotes the decay of uPA and uPAR, resulting in a decrease in the invasive capacity of these cells 1. TTP also has multiple important targets, including COX-2, HIF-1α, IL-8, IL-6, IL-8, and VEGF 34,36–40 and the oncogenic Ser/Th kinase Pim-1, which is overexpressed in several cancers and promotes cellular growth and apoptosis resistance 41,42. Thus, TTP appears to be a down-regulator of many cancer-related genes, which substantiates its anti-tumour role. "
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    ABSTRACT: The activities of RNA binding proteins are perturbed in several pathological conditions including cancer. These proteins include tristetraprolin (TTP, ZFP36) and HuR (ELAVL1) which respectively promote the decay or stability of AU-rich mRNAs. Here, we demonstrated that increased stabilization and subsequent over-expression of HuR mRNA were coupled to TTP deficiency. These findings were observed in breast cancer cell lines with an invasive phenotype and were further confirmed in ZFP36-knockout mouse fibroblasts. We show that TTP-HuR imbalance correlated with increased expression of ARE mRNAs that code for cancer invasion genes. The microRNA miR-29a was abundant in invasive breast cancer cells when compared to non-tumorigenic cell types. When normal breast cells were treated with miR-29a, HuR mRNA and protein expression were upregulated. MiR-29a recognized a seed target in the TTP 3'UTR and a cell-permeable miR-29a inhibitor increased TTP activity towards HuR 3'UTR. This led to HuR mRNA destabilization and restoration of the aberrant TTP-HuR axis. Subsequently, the cancer invasion factors, uPA, MMP-1 and MMP-13, and cell invasiveness were decreased. The TTP-HuR mRNA ratios were also perturbed in samples from invasive breast cancer patients when compared with normal tissues and were associated with invasion gene expression. This study demonstrates that an aberrant ARE-mediated pathway in invasive cancer can be normalized by targeting the aberrant and functionally coupled TTP-HuR axis, indicating a potential therapeutic approach.
    The Journal of Pathology 05/2013; 230(1). DOI:10.1002/path.4178 · 7.43 Impact Factor
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    • "The pcDNA6/V5-TTP construct has been described previously [20]. Two oligonucleotides containing ATTTA motifs of the AHRR mRNA 3 0 UTR were synthesized at Integrated DNA Technologies (Coralville, IA). "
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    ABSTRACT: The aryl hydrocarbon receptor repressor (AHRR) inhibits the transcription of the aryl hydrocarbon receptor (AHR) by binding to XRE. We report that AHRR expression is inhibited by tristetraprolin (TTP), an AU-rich element (ARE)-binding protein. Overexpression of TTP decreased the mRNA stability and protein expression of AHRR, and TTP-overexpressing cells made smaller colonies than the control. Contrarily, inhibition of TTP by siRNA increased AHRR expression. Analyses of point mutants of the AREs demonstrated that AREs were responsible for the TTP-mediated destabilization of AHRR mRNA. RNA EMSA revealed that TTP directly binds to the AHRR 3'UTR. Taken together, we demonstrate that TTP acts as a negative regulator of AHRR and may affect tumor development through induction of tumor suppressor genes as observed in MDA-MB435.
    FEBS letters 04/2013; 587(10). DOI:10.1016/j.febslet.2013.03.031 · 3.17 Impact Factor
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    • "For the normal tissue, TTP inhibits radiation-induced cytokine production and reduces inflammatory responses. At the same time, prevention of TTP inactivation would be anticipated to be deleterious for cancer cells, where TTP is known to negatively regulate the expression of urokinase plasminogen activator (uPA), uPA receptor, matrix metalloproteinase-1 (MMP-1) and VEGF, thus decreasing tumor cell growth, invasion and metastasis [52], [53]. As we have observed that radiation induces TTP inactivation via p38-mediated phosphorylation and proteasomal degradation to produce and release increased TNF-α, we could propose to target p38. "
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    ABSTRACT: The efficacy of radiation therapy for lung cancer is limited by radiation-induced lung toxicity (RILT). Although tumor necrosis factor-alpha (TNF-α) signaling plays a critical role in RILT, the molecular regulators of radiation-induced TNF-α production remain unknown. We investigated the role of a major TNF-α regulator, Tristetraprolin (TTP), in radiation-induced TNF-α production by macrophages. For studies we irradiated (4 Gy) either a mouse lung macrophage cell line, MH-S or macrophages isolated from TTP knockout mice, and studied the effects of radiation on TTP and TNF-α levels. To study the relevance, mouse lungs were irradiated with a single dose (15 Gy) and assessed at varying times for TTP alterations. Irradiation of MH-S cells caused TTP to undergo an inhibitory phosphorylation at Ser-178 and proteasome-mediated degradation, which resulted in increased TNF-α mRNA stabilization and secretion. Similarly, MH-S cells treated with TTP siRNA or macrophages isolated from (-/-) mice had higher basal levels of TNF-α, which was increased minimally after irradiation. Conversely, cells overexpressing TTP mutants defective in undergoing phosphorylation released significantly lower levels of TNF-α. Inhibition of p38, a known kinase for TTP, by either siRNA or a small molecule inhibitor abrogated radiation-induced TNF-α release by MH-S cells. Lung irradiation induced TTP phosphorylation and protein degradation and a simultaneous increase in TNF-α production in C57BL/6 mice starting 24 h post-radiation. In conclusion, irradiation of lung macrophages causes TTP inactivation via p38-mediated phosphorylation and proteasome-mediated degradation, leading to TNF-α production. These findings suggest that agents capable of blocking TTP phosphorylation or stabilizing TTP after irradiation could decrease RILT.
    PLoS ONE 02/2013; 8(2):e57290. DOI:10.1371/journal.pone.0057290 · 3.23 Impact Factor
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