Disease relevance of CUGBP1

• MBNL1 and CUGBP1 modify expanded CUG-induced toxicity in a Drosophila model of myotonic dystrophy type 1 [1].
• Accumulation of RNA CUG repeats in myotonic dystrophy type 1 (DM1) patients leads to the induction of a CUG-binding protein, CUGBP1, which increases translation of several proteins that are required for myogenesis [2].
• EWS, an RGG-type RNA-binding protein associated with Ewing sarcoma, was identified as an interacting partner for the CUG-BP homologue in a two-hybrid assay for protein-protein interactions performed with various factors involved in RNA metabolism [3].

High impact information on CUGBP1

• However, we observed increased levels of CUG-binding protein (CUG-BP1) in skeletal muscle, as seen in individuals with DM1 [4].
• Altered expression of genes regulated posttranscriptionally by CUG-BP therefore may contribute to DM pathogenesis [5].
• CUG-BP was found to bind to the human cardiac troponin T (cTNT) pre-messenger RNA and regulate its alternative splicing [5].
• EDEN-BP is highly homologous to a human protein possibly involved in myotonic dystrophy [6].
• In contrast, increasing the levels of CUGBP1 worsens (iCUG)480-induced degeneration even though CUGBP1 distribution is not altered by the expression of the expanded triplet repeat [1].

Biological context of CUGBP1

• We also report that altering the levels of two RNA-BP known to be involved in DM1 pathogenesis, MBNL1 and CUGBP1, modify the (iCUG)480 degenerative phenotypes [1].
• It was previously shown that delay of muscle differentiation and insulin resistance in DM1 are associated with misregulation of CUGBP1 protein levels [7].
• We previously identified an RNA binding protein, CUGBP1, which binds to GCN repeats located within the 5' region of C/EBPbeta mRNAs and regulates translation of C/EBPbeta isoforms [8].
• Failure of DM cells to accumulate CUGBP1 in the cytoplasm leads to a significant reduction of p21 and to alterations of other proteins responsible for the cell cycle withdrawal [9].
• Several lines of evidence show that CUGBP1 induces the translation of p21 via binding to a GC-rich sequence located within the 5' region of p21 mRNA [9].

Anatomical context of CUGBP1

• Two HeLa cell proteins, CUG-BP1 and CUG-BP2, have been purified based upon their ability to bind specifically to (CUG)8 oligonucleotides in vitro [10].
• Skeletal muscle cells from DM patients fail to induce cytoplasmic levels of a CUG RNA binding protein, CUGBP1, while normal differentiated cells accumulate CUGBP1 in the cytoplasm [9].
• Our data provide evidence for an impaired cell cycle withdrawal in DM muscle cells and suggest that alterations in the activity of CUGBP1 causes disruption of p21-dependent control of cell cycle arrest [9].
• Similarly to DM patients, overexpression of RNA CUG repeats in cultured cells results in the re-allocation of CUGBP1 from a free state to the RNA.protein complexes containing CUG repeats [11].
• Analysis of cytoplasmic and polysomal proteins from rat liver after PH showed that CUGBP1 is associated with polysomes that translate low molecular weight isoforms of C/EBPbeta [12].

Associations of CUGBP1 with chemical compounds

• Experiments with cyclohexamide-dependent block of protein synthesis showed that the half-life of CUGBP1 is increased in cells expressing CUG repeats [11].
• Tumor necrosis factor-alpha, levels of which are elevated in fat tissue with aging, increased CUGBP1 protein, CUGBP1 binding activity, and C/EBPbeta-LIP in preadipocytes from young rats [13].

Physical interactions of CUGBP1

• In vitro RNA-binding/photocrosslinking studies demonstrate that CUG-BP/hNab50 binds to RNAs containing the Mt-PK 3'-UTR [10].
• CUG-BP binds to RNA substrates and recruits PARN deadenylase [14].

Enzymatic interactions of CUGBP1

• DMPK also interacts with and phosphorylates CUG-BP/hNab50 protein in vitro [15].

Other interactions of CUGBP1

• Our data demonstrate that both CUGBP1 and CRT interact with GCU repeats within myotonin protein kinase and with GCN repeats within C/EBPalpha and C/EBPbeta mRNAs [8].
• The CUGBP1 mRNA was found to contain several CAG repeat sequences [16].
• In vitro RNA-RNA binding experiments demonstrated that the incubation of expanded CUG repeats with CUGBP1 RNA generated a higher molecular weight band, which was digested by RNase III [16].
• CUG-BP1 is thus a previously unidentified downstream target of EGFR signaling and represents a new translational regulator of LIP expression in human mammary epithelial cells [17].
• These studies showed that both the increased levels of CUGBP1 and cdk4-mediated hyper-phosphorylation of CUGBP1 are involved in the age-associated induction of the CUGBP1-eIF2 complex [18].

Analytical, diagnostic and therapeutic context of CUGBP1

• In addition, a semi-quantitative RT-PCR assay showed that the relative amount of CUGBP1 mRNA was reduced in muscle biopsy samples from 10 DM1 patients compared to that from five normal individuals (P < 0.01) and 10 myopathic disease controls (P < 0.01) [16].
• Northern blot analysis demonstrated that the quantity of CUGBP1 mRNA in three DM1 patients was approximately 70% of that observed in three normal controls (P < 0.05) [16].
• Using electron microscopy, we visualized large RNAs containing up to 130 CUG repeats and studied the binding of purified CUG-binding protein (CUG-BP) to these RNAs [19].
• Surface plasmon resonance and electrophoretic mobility-shift assays showed that these two families differed in their ability to bind CUG-BP1 [20].
• Using a combination of indirect immunofluorescence to detect endogenous proteins and overexpression of proteins with green fluorescent protein (GFP) tags we have shown that CUG-BP and hnRNP C do not co-localise with expanded repeat foci in DM1 cell lines [21].

References