AU-rich elements (AREs) in the 3' untranslated region (UTR) of unstable mRNAs dictate their degradation. An RNAi-based screen performed in Drosophila S2 cells has revealed that Dicer1, Argonaute1 (Ago1) and Ago2, components involved in microRNA (miRNA) processing and function, are required for the rapid decay of mRNA containing AREs of tumor necrosis factor-alpha. The requirement for Dicer in the instability of ARE-containing mRNA (ARE-RNA) was confirmed in HeLa cells. We further observed that miR16, a human miRNA containing an UAAAUAUU sequence that is complementary to the ARE sequence, is required for ARE-RNA turnover. The role of miR16 in ARE-RNA decay is sequence-specific and requires the ARE binding protein tristetraprolin (TTP). TTP does not directly bind to miR16 but interacts through association with Ago/eiF2C family members to complex with miR16 and assists in the targeting of ARE. miRNA targeting of ARE, therefore, appears to be an essential step in ARE-mediated mRNA degradation.

Like apoptosis, oncogene-induced senescence is a barrier to tumor development. However, relatively little is known about the signaling pathways mediating the senescence response. p38-regulated/activated protein kinase (PRAK) is a p38 MAPK substrate whose physiological functions are poorly understood. Here we describe a role for PRAK in tumor suppression by demonstrating that PRAK mediates senescence upon activation by p38 in response to oncogenic ras. PRAK deficiency in mice enhances DMBA-induced skin carcinogenesis, coinciding with compromised senescence induction. In primary cells, inactivation of PRAK prevents senescence and promotes oncogenic transformation. Furthermore, we show that PRAK activates p53 by direct phosphorylation. We propose that phosphorylation of p53 by PRAK following activation of p38 MAPK by ras plays an important role in ras-induced senescence and tumor suppression.

Dicer is essential for plant, Caenorhabditis elegans, and Drosophila antiviral responses because of its role in generating small interfering RNA (siRNA) from viral genomes. We show that because of impaired miRNA production, mice with a variant Dicer1 allele (Dicer1(d/d)) were more susceptible to vesicular stomatitis virus (VSV) infection. We did not detect VSV genome-derived siRNA in wild-type cells or any alteration of interferon-mediated antiviral responses by Dicer1 deficiency. Rather, we found that host miR24 and miR93 could target viral large protein (L protein) and phosphoprotein (P protein) genes, and a lack of miR24 and miR93 was responsible for increased VSV replication in Dicer1(d/d) cells. Our data suggest that host miRNA can play a role in host interactions with viruses.

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Clostridium perfringens type B or D isolates, which cause enterotoxemias or enteritis in livestock, produce epsilon toxin (ETX). ETX is exceptionally potent, earning it a listing as a CDC class B select toxin. Most C. perfringens strains also express up to three different sialidases, although the possible contributions of those enzymes to type B or D pathogenesis remain unclear. Type D isolate CN3718 was found to carry two genes (nanI and nanJ) encoding secreted sialidases and one gene (nanH) encoding a cytoplasmic sialidase. Construction in CN3718 of single nanI, nanJ and nanH null mutants, as well as a nanI/nanJ double null mutant and a triple sialidase null mutant, identified NanI as the major secreted sialidase of this strain. Pretreating MDCK cells with NanI sialidase, or with culture supernatants of BMC206 (an isogenic CN3718 etx null mutant that still produces sialidases) enhanced the subsequent binding and cytotoxic effects of purified ETX. Complementation of BMC207 (an etx/nanH/nanI/nanJ null mutant) showed this effect is mainly attributable to NanI production. Contact between BMC206 and certain mammalian cells (e.g., enterocyte-like Caco-2 cells) resulted in more rapid sialidase production and this effect involved increased transcription of BMC206 nanI gene. BMC206 was shown to adhere to some (e.g. Caco-2 cells), but not all mammalian cells, and this effect was dependent upon sialidase, particularly NanI, expression. Finally, the sialidase activity of NanI (but not NanJ or NanH) could be enhanced by trypsin. Collectively these in vitro findings suggest that, during type D disease originating in the intestines, trypsin may activate NanI, which (in turn) could contribute to intestinal colonization by C. perfringens type D isolates and also increase ETX action.

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The majority of human prostate cancer cell lines, including the two "classical" cell lines DU-145 and PC-3, are reported to be androgen receptor (AR)-negative. However, other studies have provided evidence that the DU-145 and PC-3 cell lines express AR mRNA. These contradictory observations prompted us to investigate whether DU-145 and PC-3 cell lines express the androgen receptor. Using antipeptide antibodies directed against three distinct regions of the human AR protein and an improved method to detect AR protein in immunoblotting, we report that DU-145 and PC-3 cell lines express AR protein. We found that the relative levels of the AR mRNA and protein that were detected in DU-145 and PC-3 cell lines were lower than the LNCaP, an AR-positive cell line. Moreover, the antibody directed against the non-variant region (amino acids 299-315), but not the variant N- or C-terminal region (amino acids 1-20 and 900-919, respectively) of the human AR protein, detected the expression of AR in all prostate cancer cell lines. Notably, treatment of these cell lines with dihydrotestosterone (DHT) resulted in measurable increases in the AR protein levels and considerable nuclear accumulation. Although, treatment of DU-145 and PC-3 cells with DHT did not result in stimulation of the activity of an AR-responsive reporter, knockdown of AR expression in PC-3 cells resulted in decreases in p21(CIP1) protein levels, and a measurable decrease in the activity of the p21-luc-reporter. Our observations demonstrate the expression of AR protein in DU-145 and PC-3 prostate cancer cell lines.

BackgroundAlthough useful for probing bacterial pathogenesis and physiology, current random mutagenesis systems suffer limitations for studying the toxin-producing bacterium Clostridium perfringens.Methodology/Principal FindingsAn EZ-Tn5-based random mutagenesis approach was developed for use in C. perfringens. This mutagenesis system identified a new regulatory locus controlling toxin production by strain 13, a C. perfringens type A strain. The novel locus, encoding proteins with homology to the AgrB and AgrD components of the Agr quorum sensing system of Staphylococcus aureus and two hypothetical proteins, was found to regulate early production of both alpha toxin and perfringolysin O (PFO) by strain 13. PFO production by the strain 13 ΔagrB mutant could be restored by genetic complementation or by physical complementation, i.e. by co-culture of the strain 13 ΔagrB mutant with a pfoA mutant of either strain 13 or C. perfringens type C CN3685. A similar AgrB- and AgrD-encoding locus is identifiable in all sequenced C. perfringens strains, including type B, C, D, and E isolates, suggesting this regulatory locus contributes to toxin regulation by most C. perfringens strains. In strain 13, the agrB and agrD genes were found to be co-transcribed in an operon with two upstream genes encoding hypothetical proteins.Conclusions/SignificanceThe new Tn5-based random mutagenesis system developed in this study is more efficient and random than previously reported C. perfringens random mutagenesis approaches. It allowed identification of a novel C. perfringens toxin regulatory locus with homology to the Agr system of S. aureus and which functions as expected of an Agr-like quorum sensing system. Since previous studies have shown that alpha toxin and perfringolysin O are responsible for strain 13-induced clostridial myonecrosis in the mouse model, the new agr regulatory locus may have importance for strain 13 virulence.