Polyamines Regulate c-Myc Translation through Chk2-dependent HuR Phosphorylation

All mammalian cells depend on polyamines for normal growth and proliferation, but the exact roles of polyamines at the molecular level remain largely unknown. The RNA-binding protein HuR modulates the stability and translation of many target mRNAs. Here, we show that in rat intestinal epithelial cells (IECs), polyamines enhanced HuR association with the 3′-untranslated region of the c-Myc mRNA by increasing HuR phosphorylation by Chk2, in turn promoting c-Myc translation. Depletion of cellular polyamines inhibited Chk2 and reduced the affinity of HuR for c-Myc mRNA; these effects were completely reversed by addition of the polyamine putrescine or by Chk2 overexpression. In cells with high content of cellular polyamines, HuR silencing or Chk2 silencing reduced c-Myc translation and c-Myc expression levels. Our findings demonstrate that polyamines regulate c-Myc translation in IECs through HuR phosphorylation by Chk2 and provide new insight into the molecular functions of cellular polyamines.

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S1764 Polyamines Regulate the Stability and Translation of MEK-1 mRNA Through RNA-Binding Protein HuR Modulating Apoptosis in Intestinal Epithelial Cells

Gastroenterology ◽

10.1016/s0016-5085(09)61207-5 ◽

2009 ◽

Vol 136 (5) ◽

pp. A-265

Author(s):

Pengyuan Wang ◽

Rao N. Jaladanki ◽

Tongtong Zou ◽

Lan Liu ◽

Lan Xiao ◽

...

Keyword(s):

Epithelial Cells ◽

Rna Binding ◽

Intestinal Epithelial Cells ◽

Binding Protein ◽

Rna Binding Protein ◽

Intestinal Epithelial ◽

The Stability

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Regulation of cyclin-dependent kinase 4 translation through CUG-binding protein 1 and microRNA-222 by polyamines

Molecular Biology of the Cell ◽

10.1091/mbc.e11-01-0069 ◽

2011 ◽

Vol 22 (17) ◽

pp. 3055-3069 ◽

Cited By ~ 48

Author(s):

Lan Xiao ◽

Yu-Hong Cui ◽

Jaladanki N. Rao ◽

Tongtong Zou ◽

Lan Liu ◽

...

Keyword(s):

Mammalian Cells ◽

Untranslated Region ◽

Molecular Level ◽

Intestinal Epithelial Cells ◽

Binding Protein ◽

Intestinal Epithelial ◽

Cyclin Dependent Kinase ◽

Coding Region ◽

Processing Bodies ◽

Cdk4 Expression

The amino acid–derived polyamines are organic cations that are essential for growth in all mammalian cells, but their exact roles at the molecular level remain largely unknown. Here we provide evidence that polyamines promote the translation of cyclin-dependent kinase 4 (CDK4) by the action of CUG-binding protein 1 (CUGBP1) and microRNA-222 (miR-222) in intestinal epithelial cells. Both CUGBP1 and miR-222 were found to bind the CDK4 mRNA coding region and 3′-untranslated region and repressed CDK4 translation synergistically. Depletion of cellular polyamines increased cytoplasmic CUGBP1 abundance and miR-222 levels, induced their associations with the CDK4 mRNA, and inhibited CDK4 translation, whereas increasing the levels of cellular polyamines decreased CDK4 mRNA interaction with CUGBP1 and miR-222, in turn inducing CDK4 expression. Polyamine-deficient cells exhibited an increased colocalization of tagged CDK4 mRNA with processing bodies; this colocalization was abolished by silencing CUGBP1 and miR-222. Together, our findings indicate that polyamine-regulated CUGBP1 and miR-222 modulate CDK4 translation at least in part by altering the recruitment of CDK4 mRNA to processing bodies.

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Transcriptional regulation of importin-α1 by JunD modulates subcellular localization of RNA-binding protein HuR in intestinal epithelial cells

AJP Cell Physiology ◽

10.1152/ajpcell.00209.2016 ◽

2016 ◽

Vol 311 (6) ◽

pp. C874-C883 ◽

Cited By ~ 2

Author(s):

Yan Xu ◽

Jie Chen ◽

Lan Xiao ◽

Hee Kyoung Chung ◽

Yuan Zhang ◽

...

Keyword(s):

Epithelial Cells ◽

Subcellular Localization ◽

Rna Binding ◽

Nuclear Translocation ◽

Intestinal Epithelial Cells ◽

Binding Protein ◽

Rna Binding Protein ◽

Intestinal Epithelial ◽

Mucosal Regeneration ◽

Importin Α

The RNA-binding protein HuR is crucial for normal intestinal mucosal regeneration by modulating the stability and translation of target mRNAs, but the exact mechanism underlying HuR trafficking between the cytoplasm and nucleus remains largely unknown. Here we report a novel function of transcription factor JunD in the regulation of HuR subcellular localization through the control of importin-α1 expression in intestinal epithelial cells (IECs). Ectopically expressed JunD specifically inhibited importin-α1 at the transcription level, and this repression is mediated via interaction with CREB-binding site that was located at the proximal region of importin-α1 promoter. Reduction in the levels of importin-α1 by JunD increased cytoplasmic levels of HuR, although it failed to alter whole cell HuR levels. Increased levels of endogenous JunD by depleting cellular polyamines also inhibited importin-α1 expression and increased cytoplasmic HuR levels, whereas JunD silencing rescued importin-α1 expression and enhanced HuR nuclear translocation in polyamine-deficient cells. Moreover, importin-α1 silencing protected IECs against apoptosis, which was prevented by HuR silencing. These results indicate that JunD regulates HuR subcellular distribution by downregulating importin-α1, thus contributing to the maintenance of gut epithelium homeostasis.

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Competitive binding of CUGBP1 and HuR to occludin mRNA controls its translation and modulates epithelial barrier function

Molecular Biology of the Cell ◽

10.1091/mbc.e12-07-0531 ◽

2013 ◽

Vol 24 (2) ◽

pp. 85-99 ◽

Cited By ~ 50

Author(s):

Ting-Xi Yu ◽

Jaladanki N. Rao ◽

Tongtong Zou ◽

Lan Liu ◽

Lan Xiao ◽

...

Keyword(s):

Barrier Function ◽

Untranslated Region ◽

Rna Binding ◽

Rna Binding Proteins ◽

Cell Monolayer ◽

Intestinal Epithelial ◽

Processing Bodies ◽

Epithelial Barrier Function ◽

P Bodies ◽

The Stability

RNA-binding proteins CUG-binding protein 1 (CUGBP1) and HuR are highly expressed in epithelial tissues and modulate the stability and translation of target mRNAs. Here we present evidence that CUGBP1 and HuR jointly regulate the translation of occludin and play a crucial role in the maintenance of tight junction (TJ) integrity in the intestinal epithelial cell monolayer. CUGBP1 and HuR competed for association with the same occludin 3′-untranslated region element and regulated occludin translation competitively and in opposite directions. CUGBP1 overexpression decreased HuR binding to occludin mRNA, repressed occludin translation, and compromised the TJ barrier function, whereas HuR overexpression inhibited CUGBP1 association with occludin mRNA and promoted occludin translation, thereby enhancing the barrier integrity. Repression of occludin translation by CUGBP1 was due to the colocalization of CUGBP1 and tagged occludin RNA in processing bodies (P-bodies), and this colocalization was prevented by HuR overexpression. These findings indicate that CUGBP1 represses occludin translation by increasing occludin mRNA recruitment to P-bodies, whereas HuR promotes occludin translation by blocking occludin mRNA translocation to P-bodies via the displacement of CUGBP1.

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Novel intestinal splice variants of RNA-binding protein CUGBP2: isoform-specific effects on mitotic catastrophe

AJP Gastrointestinal and Liver Physiology ◽

10.1152/ajpgi.00540.2007 ◽

2008 ◽

Vol 294 (4) ◽

pp. G971-G981 ◽

Cited By ~ 22

Author(s):

Satish Ramalingam ◽

Gopalan Natarajan ◽

Chris Schafer ◽

Dharmalingam Subramaniam ◽

Randal May ◽

...

Keyword(s):

Epithelial Cells ◽

Rna Binding ◽

Intestinal Epithelial Cells ◽

Splice Variants ◽

Binding Protein ◽

Rna Binding Protein ◽

Cyclin B1 ◽

Mitotic Catastrophe ◽

Intestinal Epithelial ◽

Cox 2

CUG triplet repeat-binding protein 2 (CUGBP2) is a RNA-binding protein that regulates mRNA translation and modulates apoptosis. Here, we report the identification of two splice variants (termed variants 2 and 3) in cultured human intestinal epithelial cells and in mouse gastrointestinal tract. The variants are generated from alternative upstream promoters resulting in the inclusion of additional NH2-terminal residues. Although variant 2 is the predominant isoform in normal intestine, its expression is reduced, whereas variant 1 is overexpressed following γ-irradiation. All three variants bind cyclooxygenase-2 (COX-2) mRNA. However, only variant 1 inhibits the translation of the endogenous COX-2 mRNA and a chimeric luciferase mRNA containing the COX-2 3′untranslated region. Furthermore, whereas variant 1 is predominantly nuclear, variants 2 and 3 are predominantly cytoplasmic. These data imply that the additional amino acids affect CUGBP2 function. Previous studies have demonstrated that variant 1 induces intestinal epithelial cells to undergo apoptosis. However, in contrast to variant 1, the two novel variants do not affect proliferation or apoptosis of HCT116 cells. In addition, only variant 1 induced G2/M cell cycle arrest, which was overcome by prostaglandin E2. Moreover, variant 1 increased cellular levels of phosphorylated p53 and Bax and decreased Bcl2. Caspase-3 and -9 were also activated, suggesting the initiation of the intrinsic apoptotic pathway. Furthermore, increased phosphorylation of checkpoint kinase (Chk)1 and Chk2 kinases and increased nuclear localization of Cdc2 and cyclin B1 suggested that cells were in mitotic transition. Taken together, these data demonstrate that cells expressing CUGBP2 variant 1 undergo apoptosis during mitosis, suggesting mitotic catastrophe.

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