PKR protects colonic epithelium against colitis through the unfolded protein response and prosurvival signaling

Background: The dsRNA‐activated protein kinase (PKR) phosphorylates the α subunit of eukaryotic translation initiation factor 2 (eIF2α), a global regulator of protein synthesis in mammals. In addition, PKR activates several signal transduction pathways including STAT3 and AKT. PKR is activated by a number of inflammatory stimuli that are induced in the inflamed intestine. In this study we intended to determine the role of PKR in colonic epithelial cells during experimental colitis in mice. Methods: Age‐ and sex‐matched PKR +/+,+/− and PKR −/− littermate mice were reconstituted with wildtype bone marrow cells and subjected to dextran sodium sulfate (DSS)‐induced colitis. Results: PKR −/− mice displayed more severe clinical and histological manifestations upon DSS colitis compared with their PKR +/+,+/− littermates. In response to DSS colitis, the colonic epithelial cells of PKR −/− mice exhibited impaired activation of the unfolded protein response (UPR) signaling, including eIF2α phosphorylation, endoplasmic reticulum (ER) chaperone response, and ER‐associated degradation (ERAD) components, as well as antioxidative stress response. In addition, the phosphorylation of STAT3 and AKT, which are protective against epithelial cell death and colonic inflammation, was also impaired in the colonic epithelial cells of PKR −/− mice upon DSS colitis. Conclusions: These data demonstrate that PKR is a physiologically relevant transducer of inflammatory response signaling in colonic epithelial cells. PKR may promote the homeostasis and survival of intestinal epithelial cells (IECs) through eIF2α‐mediated UPR activation, as well as the activation of STAT3 and AKT pathways. In the absence of PKR, the survival and proliferation of IECs was impaired, thus exacerbating intestinal inflammation. (Inflamm Bowel Dis 2012;)Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/93506/1/22878_ftp.pd

Involvement of yeast HSP90 isoforms in response to stress and cell death induced by acetic acid

Acetic acid-induced apoptosis in yeast is accompanied by an impairment of the general protein synthesis machinery, yet paradoxically also by the up-regulation of the two isoforms of the heat shock protein 90 (HSP90) chaperone family, Hsc82p and Hsp82p. Herein, we show that impairment of cap-dependent translation initiation induced by acetic acid is caused by the phosphorylation and inactivation of eIF2 alpha by Gcn2p kinase. A microarray analysis of polysome-associated mRNAs engaged in translation in acetic acid challenged cells further revealed that HSP90 mRNAs are over-represented in this polysome fraction suggesting preferential translation of HSP90 upon acetic acid treatment. The relevance of HSP90 isoform translation during programmed cell death (PCD) was unveiled using genetic and pharmacological abrogation of HSP90, which suggests opposing roles for HSP90 isoforms in cell survival and death. Hsc82p appears to promote survival and its deletion leads to necrotic cell death, while Hsp82p is a pro-death molecule involved in acetic acid-induced apoptosis. Therefore, HSP90 isoforms have distinct roles in the control of cell fate during PCD and their selective translation regulates cellular response to acetic acid stress.This work was supported by Fundacao para a Ciencia e Tecnologia and COMPETE/QREN/EU (PTDC/BIA-MIC/114116/2009), and by the Canadian Institute for Health Research (MOP 89737 to MH). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript

IRES-Mediated Translation of Utrophin A Is Enhanced by Glucocorticoid Treatment in Skeletal Muscle Cells

Glucocorticoids are currently the only drug treatment recognized to benefit Duchenne muscular dystrophy (DMD) patients. The nature of the mechanisms underlying the beneficial effects remains incompletely understood but may involve an increase in the expression of utrophin. Here, we show that treatment of myotubes with 6α−methylprednisolone-21 sodium succinate (PDN) results in enhanced expression of utrophin A without concomitant increases in mRNA levels thereby suggesting that translational regulation contributes to the increase. In agreement with this, we show that PDN treatment of cells transfected with monocistronic reporter constructs harbouring the utrophin A 5′UTR, causes an increase in reporter protein expression while leaving levels of reporter mRNAs unchanged. Using bicistronic reporter assays, we further demonstrate that PDN enhances activity of an Internal Ribosome Entry Site (IRES) located within the utrophin A 5′UTR. Analysis of polysomes demonstrate that PDN causes an overall reduction in polysome-associated mRNAs indicating that global translation rates are depressed under these conditions. Importantly, PDN causes an increase in the polysome association of endogenous utrophin A mRNAs and reporter mRNAs harbouring the utrophin A 5′UTR. Additional experiments identified a distinct region within the utrophin A 5′UTR that contains the inducible IRES activity. Together, these studies demonstrate that a translational regulatory mechanism involving increased IRES activation mediates, at least partially, the enhanced expression of utrophin A in muscle cells treated with glucocorticoids. Targeting the utrophin A IRES may thus offer an important and novel therapeutic avenue for developing drugs appropriate for DMD patients

Inhibitors of apoptosis proteins in human cervical cancer

BACKGROUND: It has been shown that IAPs, in particular XIAP, survivin and c-IAP1, are overexpressed in several malignancies. In the present study we investigate the expression of c-IAP1, c-IAP2, XIAP and survivin and its isoforms in cervical cancer. METHODS: We used semiquantitative RT-PCR assays to analyze 41 cancer and 6 normal tissues. The study included 8 stage I cases; 16 stage II; 17 stageIII; and a control group of 6 samples of normal cervical squamous epithelial tissue. RESULTS: c-IAP2 and XIAP mRNA levels were similar among the samples, cervical tumors had lower c-IAP1 mRNA levels. Unexpectedly, a clear positive association was found between low levels of XIAP and disease relapse. A log-rank test showed a significant inverse association (p = 0.02) between XIAP expression and tumor aggressiveness, as indicated by disease relapse rates. There were no statistically significant differences in the presence or expression levels of c-IAP1 and c-IAP2 among any of the clinical variables studied. Survivin and its isoforms were undetectable in normal cervical tissues, in contrast with the clear upregulation observed in cancer samples. We found no association between survivin expression and age, clinical stage, histology or menopausal state. Nevertheless, we found that adenocarcinoma tumors expressed higher levels of survivin 2B and DeltaEx3 (p = 0.001 and p = 0.04 respectively, by Kruskal-Wallis). A multivariate Cox's partial likelihood-based analysis showed that only FIGO stage was an independent predictor of outcome. CONCLUSION: There are no differences in the expression of c-IAP2 and XIAP between normal vs. cancer samples, but XIAP expression correlate in cervical cancer with relapse of this disease in the patients. Otherwise, c-IAP1 was downregulated in the cervical cancer samples. The expression of survivin was upregulated in the patients with cervical cancer. We have found that adenocarcinoma presented higher levels of survivin isoforms 2B and DeltaEx3

Translation initiation and its deregulation during tumorigenesis

Regulation of protein synthesis at the level of translation initiation is fundamentally important for the control of cell proliferation under normal physiological conditions. Conversely, misregulation of protein synthesis is emerging as a major contributory factor in cancer development. Most bulk protein synthesis is initiated via recognition of the mRNA 5′ cap and subsequent recognition of the initiator AUG codon by a directional scanning mechanism. However, several key regulators of tumour development are translated by a cap-independent pathway. Here we review eukaryotic translation initiation, its regulation and the ways in which this regulation can break down during tumorigenesis

Double inhibition of XIAP and Bcl-2 axis is beneficial for retrieving sensitivity of renal cell cancer to apoptosis

Renal cell carcinoma (RCC) is known to be resistant to chemo- and radiotherapy due to a high apoptotic threshold. Smac and XIAP (X-linked inhibitor of apoptosis protein) proteins were detected in all RCC cell lines and tissue samples examined. We modulated the function of XIAP, either through its constitutional downregulation with an shRNA vector or by applying a Smac-mimicking peptide. Among RCC cell lines, Caki1 expresses the highest levels of XIAP. We transfected Caki1 with XIAP-targeting shRNA vector and generated stable clones. XIAP was knocked down by RNA interference in clone no. 14 by 81.6% and in clone no. 19 by 85.3%. Compared to the parental and mock-transfected cells, neither clone was more sensitive to conventional chemotherapeutic agents, but both clones were more susceptible to Fas stimulation (P<0.0001) and to pharmacological Bcl-2 inhibition (P<0.0001), as well as to a combination of the two (P<0.0001). Mature Smac binds to XIAP via the N-terminal residues, disrupting its interaction with caspases and promoting their activity. We determined that exposure of Caki1 cells to Smac-N7 peptide (AVPIAQK) resulted in a slight but significant decrease in viability (P=0.0031) and potentiated cisplatin's effect (P=0.0027). In contrast with point targeting of XIAP by shRNA, Smac-N7 peptide is active against several IAP (inhibitor of apoptosis protein) family members, which can explain its role in sensitising cells to cisplatin. Our results suggest that multiple targeting of both Bcl-2 and XIAP or, alternatively, of several IAP family members by the Smac-N7 peptide is a potent way to overcome resistance of RCC to apoptosis-triggering treatment modalities, and might be a new tool for molecular targeted therapy

Role of Polypyrimidine Tract Binding Protein in Mediating Internal Initiation of Translation of Interferon Regulatory Factor 2 RNA

BACKGROUND: Earlier we have reported translational control of interferon regulatory factor 2 (IRF2) by internal initiation (Dhar et al, Nucleic Acids Res, 2007). The results implied possible role of IRF2 in controlling the intricate balance of cellular gene expression under stress conditions in general. Here we have investigated the secondary structure of the Internal Ribosome Entry Site of IRF2 RNA and demonstrated the role of PTB protein in ribosome assembly to facilitate internal initiation. METHODOLOGY/PRINCIPAL FINDINGS: We have probed the putative secondary structure of the IRF2 5'UTR RNA using various enzymatic and chemical modification agents to constrain the secondary structure predicted from RNA folding algorithm Mfold. The IRES activity was found to be influenced by the interaction of trans-acting factor, polypyrimidine tract binding protein (PTB). Deletion of 25 nts from the 3'terminus of the 5'untranslated region resulted in reduced binding with PTB protein and also showed significant decrease in IRES activity compared to the wild type. We have also demonstrated putative contact points of PTB on the IRF2-5'UTR using primer extension inhibition assay. Majority of the PTB toe-prints were found to be restricted to the 3'end of the IRES. Additionally, Circular Dichroism (CD) spectra analysis suggested change in the conformation of the RNA upon PTB binding. Further, binding studies using S10 extract from HeLa cells, partially silenced for PTB gene expression, resulted in reduced binding by other trans-acting factors. Finally, we have demonstrated that addition of recombinant PTB enhances ribosome assembly on IRF2 IRES suggesting possible role of PTB in mediating internal initiation of translation of IRF2 RNA. CONCLUSION/SIGNIFICANCE: It appears that PTB binding to multiple sites within IRF2 5'UTR leads to a conformational change in the RNA that facilitate binding of other trans-acting factors to mediate internal initiation of translation

Rapamycin activation of 4E-BP prevents parkinsonian dopaminergic neuron loss

Mutations in PINK1 and PARK2 cause autosomal recessive parkinsonism, a neurodegenerative disorder that is characterized by the loss of dopaminergic neurons. To discover potential therapeutic pathways, we identified factors that genetically interact with Drosophila park and Pink1. We found that overexpression of the translation inhibitor Thor (4E-BP) can suppress all of the pathologic phenotypes, including degeneration of dopaminergic neurons in Drosophila. 4E-BP is activated in vivo by the TOR inhibitor rapamycin, which could potently suppress pathology in Pink1 and park mutants. Rapamycin also ameliorated mitochondrial defects in cells from individuals with PARK2 mutations. Recently, 4E-BP was shown to be inhibited by the most common cause of parkinsonism, dominant mutations in LRRK2. We also found that loss of the Drosophila LRRK2 homolog activated 4E-BP and was also able to suppress Pink1 and park pathology. Thus, in conjunction with recent findings, our results suggest that pharmacologic stimulation of 4E-BP activity may represent a viable therapeutic approach for multiple forms of parkinsonism