Design of Novel Relaxase Substrates Based on Rolling Circle Replicases for Bioconjugation to DNA Nanostructures

During bacterial conjugation and rolling circle replication, HUH endonucleases, respectively known as relaxases and replicases, form a covalent bond with ssDNA when they cleave their target sequence (nic site). Both protein families show structural similarity but limited amino acid identity. Moreover, the organization of the inverted repeat (IR) and the loop that shape the nic site differs in both proteins. Arguably, replicases cleave their target site more efficiently, while relaxases exert more biochemical control over the process. Here we show that engineering a relaxase target by mimicking the replicase target, results in enhanced formation of protein-DNA covalent complexes. Three widely different relaxases, which belong to MOBF, MOBQ and MOBP families, can properly cleave DNA sequences with permuted target sequences. Collaterally, the secondary structure that the permuted targets acquired within a supercoiled plasmid DNA resulted in poor conjugation frequencies underlying the importance of relaxase accessory proteins in conjugative DNA processing. Our results reveal that relaxase and replicase targets can be interchangeable in vitro. The new Rep substrates provide new bioconjugation tools for the design of sophisticated DNA-protein nanostructures.This work was financed by grants BFU2014-55534-C2-1-P from the Spanish Ministry of Economy and Competitiveness and 612146/FP7-ICT- 2013 and 282004/FP7-HEALTH.2011.2.3.1-2 from the European Union Seventh Framework Programme to FC and grant BFU2014-55534-C2-2-P from the Spanish Ministry of Economy and Competitiveness to GM. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript

Transgenic Expression of Entire Hepatitis B Virus in Mice Induces Hepatocarcinogenesis Independent of Chronic Liver Injury

Hepatocellular carcinoma (HCC), the third leading cause of cancer deaths worldwide, is most commonly caused by chronic hepatitis B virus (HBV) infection. However, whether HBV plays any direct role in carcinogenesis, other than indirectly causing chronic liver injury by inciting the host immune response, remains unclear. We have established two independent transgenic mouse lines expressing the complete genome of a mutant HBV (“preS2 mutant”) that is found at much higher frequencies in people with HCC than those without. The transgenic mice show evidence of stress in the endoplasmic reticulum (ER) and overexpression of cyclin D1 in hepatocytes. These mice do not show any evidence of chronic liver injury, but by 2 years of age a majority of the male mice develop hepatocellular neoplasms, including HCC. Unexpectedly, we also found a significant increase in hepatocarcinogenesis independent of necroinflammation in a transgenic line expressing the entire wildtype HBV. As in the mutant HBV mice, HCC was found only in aged—2-year-old—mice of the wildtype HBV line. The karyotype in all the three transgenic lines appears normal and none of the integration sites of the HBV transgene in the mice is near an oncogene or tumor suppressor gene. The significant increase of HCC incidence in all the three transgenic lines—expressing either mutant or wildtype HBV—therefore argues strongly that in absence of chronic necroinflammation, HBV can contribute directly to the development of HCC

Is pre-treatment liver biopsy necessary for all hepatitis C genotypes?

Background. Current practice guidelines recommend liver biopsy prior to treatment of hepatitis C genotype-1 but not for genotype-2/3; this is based on expert opinion, not on published evidence. Methods. In retrospective analysis of a large trial database prior to the publication of recent guidelines, we compared outcomes in 985 treatment-naïve patients with hepatitis C who did or did not undergo liver biopsy before starting peginterferon alfa-2a plus ribavirin. Results. Physicians elected to treat 141/654 (21.6%) genotype-1 patients and 126/331 (38.1%) genotype-2/3 patients without liver biopsy. There were no differences in baseline characteristics among those with or without pre-treatment liver biopsy, except for female preponderance in genotype-1 patients with liver biopsy. The sustained viral response (SVR) rate was no different amongst genotype-2/3 patients who had a biopsy before treatment with 66.3% SVR vs. 69.8% of those treated without biopsy (p = 0.546), but significantly higher among genotype-1 patients with pre-treatment liver biopsy at 54.6 vs. 44.0% for those treated without a liver biopsy (p = 0.029). In genotype-1 patients with liver biopsy, more patients with cirrhosis had dose adjustments (p = 0.0057) rather than drug discontinuation. There was tendency for earlier discontinuation among patients without pre-treatment liver biopsy. Conclusions. Pre-treatment liver biopsy was associated with better SVR amongst genotype-1 patients. This improvement may reflect ongoing commitment to completing the treatment course by both patient and physician. In genotype-2/3 patients, pre-treatment liver biopsy may not be essential to maximize SVR rates. This study validates the recommendations of the most recent treatment guidelines for hepatitis C

Small molecules intercept Notch signaling and the early secretory pathway

Notch signaling has a pivotal role in numerous cell-fate decisions, and its aberrant activity leads to developmental disorders and cancer. To identify molecules that influence Notch signaling, we screened nearly 17,000 compounds using automated microscopy to monitor the trafficking and processing of a ligand-independent Notch–enhanced GFP (eGFP) reporter. Characterization of hits in vitro by biochemical and cellular assays and in vivo using zebrafish led to five validated compounds, four of which induced accumulation of the reporter at the plasma membrane by inhibiting γ-secretase. One compound, the dihydropyridine FLI-06, disrupted the Golgi apparatus in a manner distinct from that of brefeldin A and golgicide A. FLI-06 inhibited general secretion at a step before exit from the endoplasmic reticulum (ER), which was accompanied by a tubule-to-sheet morphological transition of the ER, rendering FLI-06 the first small molecule acting at such an early stage in secretory traffic. These data highlight the power of phenotypic screening to enable investigations of central cellular signaling pathways

Systemic Administration of Abeta mAb Reduces Retinal Deposition of Abeta and Activated Complement C3 in Age-Related Macular Degeneration Mouse Model

<div><p>Age-related macular degeneration (AMD) is a leading cause of legal blindness in the Western world. There are effective treatments for the vascular complications of neo-vascular AMD, but no effective therapies are available for the dry/atrophic form of the disease. A previously described transgenic CFH-gene deficient mouse model, (<i>cfh−/−</i>), shows hallmarks of early AMD. The ocular phenotype has been further analysed to demonstrate amyloid beta (Aβ) rich basement membrane deposits associated with activated complement C3. <i>Cfh−/−</i> mice were treated systemically in both prophylactic and therapeutic regimes with an anti-Aβ monoclonal antibody (mAb), 6F6, to determine the effect on the <i>cfh−/−</i> retinal phenotype. Prophylactic treatment with 6F6 demonstrated a dose dependent reduction in the accumulation of both Aβ and activated C3 deposition. A similar reduction in the retinal endpoints could be seen after therapeutic treatment. Serum Aβ levels after systemic administration of 6F6 show accumulation of Aβ in the periphery suggestive of a peripheral sink mechanism. In summary, anti-Aβ mAb treatment can partially prevent or reverse ocular phenotypes of the <i>cfh−/−</i> mouse. The data support this therapeutic approach in humans potentially modulating two key elements in the pathogenesis of AMD – Aβ and activated, complement C3.</p></div