Polyglutamine (polyQ) diseases are a class of dominantly-inherited neurodegenerative disorders caused by the expansion of a CAG repeat encoding glutamine within the coding region of the respective genes 1. The molecular and cellular pathways underlying polyQ-induced neurodegeneration are the focus of much research, and it is widely viewed that toxic activities of the protein, resulting from the abnormally long polyQ tract, cause pathogenesis 2, 3. We now provide evidence for a pathogenic role of the CAG repeat RNA in polyQ toxicity using Drosophila. In a Drosophila screen for modifiers of polyQ degeneration induced by the Spinocerebellar ataxia type 3 (SCA3) protein ataxin-3, we isolated an upregulation allele of muscleblind (mbl), a gene implicated in the RNA toxicity of CUG expansion diseases 4-6. Further analysis indicated that there may be a toxic role of the RNA in polyQ-induced degeneration. We tested the role of the RNA by altering the CAG repeat sequence to an interrupted CAACAG repeat within the polyQ-encoding region; this dramatically mitigated toxicity. In addition, expression of an untranslated CAG repeat of pathogenic length conferred neuronal degeneration. These studies reveal a role for the RNA in polyQ toxicity, highlighting common components in RNA-based and polyQ protein-based trinucleotide repeat expansion diseases.To identify modifiers that add new insight into ataxin-3 pathogenesis, we performed an overexpression EP screen with a Drosophila model of ataxin-3 7 for modifiers of eye degeneration. Seven new EP-element insertional mutations were isolated; one of these (B2-E1) dramatically enhanced toxicity, causing severe pigmentation loss and striking collapse of the retina, but had no effect on its own when directed to the eye (Fig. 1a-d). Molecular analysis showed that the B2-E1 insertion was in the promoter of the mbl gene, and upregulated gene expression ( Supplementary Fig. S2). As Mbl has been implicated as a modifier of CUG repeat RNA toxicity 4-6, these results suggested an unexpected role for mbl as a modulator of polyQ protein toxicity.We confirmed that mbl upregulation enhanced polyQ toxicity by generating transgenic flies bearing a mbl cDNA (MblA, which is implicated in eye and photoreceptor (PR) neuron development 8). As with the original EP insertion, flies expressing MblA showed strongly enhanced SCA3trQ61 toxicity, as well as enhanced photoreceptor (PR) degeneration when expressed with rh1-GAL4, but MblA had no effect on its own (Fig. 1e-h, Supplementary Fig. S3). B2-E1 and MblA enhanced toxicity of full-length pathogenic forms of ataxin-3 as well as truncated versions, and enhanced the toxicity of pathogenic forms of the Huntington's disease protein ( Supplementary Figs. S3, S4). Expression of Mbl, however, did Fig. S3d-g). Upregulation of MblA also enhanced the shortened lifespan of flies expressing SCA3trQ78 globally in the nervous system (elav-GAL4). Heterozygosity for a mbl null allele (mbl E27 or mbl E2 2) 8, 9 suppressed lifespan reduction (Fig. 1i, Supplementa...

Overexpression of HER-2/neu correlates with poor survival of breast and ovarian cancer patients and induces resistance to tumor necrosis factor (TNF), which causes cancer cells to escape from host immune defenses. The mechanism of HER-2/neu-induced TNF resistance is unknown. Here we report that HER-2/neu activates Akt and NF-B without extracellular stimulation. Blocking of the Akt pathway by a dominant-negative Akt sensitizes the HER-2/neu-overexpressing cells to TNF-induced apoptosis and inhibites IB kinases, IB phosphorylation, and NF-B activation. Our results suggested that HER-2/neu constitutively activates the Akt/ NF-B anti-apoptotic cascade to confer resistance to TNF on cancer cells and reduce host defenses against neoplasia.

Because HER-2/neu overexpression is important in cancer development, we looked for a method of suppressing the cell transformation mediated by HER-2/neu overexpression. We have identified that the DNA-binding protein PEA3, which is encoded by a previously isolated gene of the ets family, specifically targeted a DNA sequence on the HER-2/neu promoter and downregulated the promoter activity. Expression of PEA3 resulted in preferential inhibition of cell growth and tumor development of HER-2/neu-overexpressing cancer cells. This is a new approach to targeting HER-2/neu overexpression and also provides a rationale to the design for repressors of diseases caused by overexpression of pathogenic genes.

Summary microRNAs are endogenous non-coding small RNAs with important roles in many biological pathways; their generation and activity are under precise regulation [1–3]. Emerging evidence suggests that miRNA pathways are precisely modulated with controls at the level of transcription [4–8], processing [9–11] and stability [12,13], with miRNA deregulation linked with diseases [14] and neurodegenerative disorders [15]. In the Drosophila miRNA biogenesis pathway, long primary miRNA transcripts undergo sequential cleavage [16–18] to release the embedded miRNAs. Mature miRNAs are then loaded into Argonaute 1 (Ago1) within the RNA-induced silencing complex (RISC) [19,20]. Intriguingly, we found that Drosophila miR-34 displays multiple isoforms that differ at the 3'end, suggesting a novel biogenesis mechanism involving 3'end processing. To define the cellular factors responsible, we performed an RNAi screen and identified a putative 3'→5' exoribonuclease CG9247/nibbler essential for the generation of the smaller isoforms of miR-34. Nibbler (Nbr) interacts with Ago1 and processes miR-34 within RISC. Deep sequencing analysis revealed a larger set of multi-isoform miRNAs that are controlled by nibbler. These findings suggest that Nbr-mediated 3' end processing represents a critical step in miRNA maturation that impacts miRNA diversity.