Regulation of the positive transcriptional effect of PLZF through a non-canonical EZH2 activity

The transcription factor PLZF (promyelocytic leukemia zinc finger protein) acts as an epigenetic regulator balancing self-renewal and differentiation of hematopoietic cells through binding to various chromatin-modifying factors. First described as a transcriptional repressor, PLZF is also associated with active transcription, although the molecular bases underlying the differences are unknown. Here, we reveal that in a hematopoietic cell line, PLZF is predominantly associated with transcribed genes. Additionally, we identify a new association between PLZF and the histone methyltransferase, EZH2 at the genomic level. We find that co-occupancy of PLZF and EZH2 on chromatin at PLZF target genes is not associated with SUZ12 or trimethylated lysine 27 of histone H3 (H3K27me3) but with the active histone mark H3K4me3 and active transcription. Removal of EZH2 leads to an increase of PLZF binding and increased gene expression. Our results suggest a new role of EZH2 in restricting PLZF positive transcriptional activity independently of its canonical PRC2 activity.

Polo-like-kinase 1 is a proviral host factor for hepatitis B virus replication

Chronic hepatitis B virus (HBV) infection is a major risk factor for hepatocellular carcinoma (HCC) and current treatments for chronic hepatitis B and HCC are suboptimal. Herein, we identified cellular serine/threonine Polo-like-kinase 1 (PLK1) as a positive effector of HBV replication. The aim of this study was to demonstrate the proviral role of PLK1 in HBV biosynthesis and validate PLK1 inhibition a potential antiviral strategy. To this end, we employed physiologically relevant HBV infection models of primary human hepatocytes (PHHs) and differentiated HepaRG cells in conjunction with pharmacologic PLK1 inhibitors, small interfering RNA (siRNA)-mediated knockdown, and overexpression of constitutively active PLK1 (PLK1CA ). In addition, a humanized liver Fah-/- /Rag2-/- /Il2rg-/- (FRG) mouse model was used to determine the antiviral effect of PLK1 inhibitor BI-2536 on HBV infection in vivo. Finally, in vitro PLK1 kinase assays and site-directed mutagenesis were employed to demonstrate that HBV core protein (HBc) is a PLK1 substrate. We demonstrated that HBV infection activated cellular PLK1 in PHHs and differentiated HepaRG cells. PLK1 inhibition by BI-2536 or siRNA-mediated knockdown suppressed HBV DNA biosynthesis, whereas overexpression of PLK1CA increased it, suggesting that the PLK1 effects on viral biosynthesis are specific and that PLK1 is a proviral cellular factor. Significantly, BI-2536 administration to HBV-infected humanized liver FRG mice strongly inhibited HBV infection, validating PLK1 as an antiviral target in vivo. The proviral action of PLK1 is associated with the biogenesis of the nucleocapsid, as BI-2536 leads to its decreased intracellular formation/accumulation. In this respect, our studies identified HBc as a PLK1 substrate in vitro, and mapped PLK1 phosphorylation sites on this protein.

CONCLUSION

PLK1 is a proviral host factor that could be envisaged as a target for combined antiviral and antitumoral strategies against HBV infection and HBV-mediated carcinogenesis. (Hepatology 2017;66:1750-1765).

Nucleosome eviction in mitosis assists condensin loading and chromosome condensation

Condensins associate with DNA and shape mitotic chromosomes. Condensins are enriched nearby highly expressed genes during mitosis, but how this binding is achieved and what features associated with transcription attract condensins remain unclear. Here, we report that condensin accumulates at or in the immediate vicinity of nucleosome-depleted regions during fission yeast mitosis. Two transcriptional coactivators, the Gcn5 histone acetyltransferase and the RSC chromatin-remodelling complex, bind to promoters adjoining condensin-binding sites and locally evict nucleosomes to facilitate condensin binding and allow efficient mitotic chromosome condensation. The function of Gcn5 is closely linked to condensin positioning, since neither the localization of topoisomerase II nor that of the cohesin loader Mis4 is altered in gcn5 mutant cells. We propose that nucleosomes act as a barrier for the initial binding of condensin and that nucleosome-depleted regions formed at highly expressed genes by transcriptional coactivators constitute access points into chromosomes where condensin binds free genomic DNA.

Pathogens isolated during treatment failures in otitis

OBJECTIVES

A prospective study in the Paris region to evaluate the clinical and bacteriologic epidemiology of acute otitis media in infants in whom oral antibiotic therapy resulted in clinical failure.

METHODS

The study included 186 children with a mean age of 17.5 +/- 13.1 months. Two-thirds of them attended a day-care center and 40.8% had a history of recurrent otitis media. The most frequently prescribed prior antibiotics were amoxicillin-clavulanic acid (43% of cases), an oral third generation cephalosporin (22.6%), erythromycin-sulfisoxazole (11.8%) and a first generation cephalosporin (10.2%). The average duration of antibiotic therapy was 6.9 +/- 2.65 days. Specimens for bacterial cultures included 188 samples of middle ear fluid obtained by tympanocentesis and 37 collected from otorrhea fluid.

RESULTS

One hundred forty-one samples (62.7%) from 126 children yielded 170 bacterial isolates. In 60 children (32.3%) the culture of the ear pus was sterile. Among the 170 bacterial isolates: 67 (39.4%) were Streptococcus pneumoniae (59 patients), of which 77.6% had reduced susceptibility to penicillin (PRSP with penicillin MIC > or = 0.125 mg/l); 61 (35.9%) were Haemophilus influenzae (56 patients) of which 49.2% were beta-lactamase producers; and 8 were Moraxella catarrhalis (8 patients), of which 87.5% were beta-lactamase producers. Thirty-six patients were infected by S. pneumoniae with penicillin MIC > or =1 mg/l. In our study attending day-care center (P = 0.04), temperature >38 degrees C with signs of otalgia (P = 0.02), age <2 years (P = 0.048) and prior antibiotic treatment with erythromycin-sulfisoxazole (P = 0.006) were independently predictive risk factors for patients infected with penicillin-resistant S. pneumoniae. Pneumococcal serogroups 23, 14 and 19 were predominant (25.4, 25.4 and 23.8%, respectively). Penicillin resistance was mainly associated with serogroups 23 and 14.

CONCLUSIONS

Penicillin-resistant S. pneumoniae isolates are frequently responsible for therapeutic failure in cases of acute otitis media in the Paris region.

Wuchereria bancrofti filariasis in French Polynesia: age-specific patterns of microfilaremia, circulating antigen, and specific IgG and IgG4 responses according to transmission level

The age-specific patterns of microfilaremia, Og4C3 antigenemia, anti-Brugia malayi IgG and IgG4 were assessed in 3 villages of low, medium and high transmission level for Wuchereria bancrofti filariasis. The prevalence rates for each of the 4 markers were clearly age dependent and their patterns strongly associated with the transmission level. The antigenemia prevalence rate was consistently higher than the microfilaremia prevalence rate, in all age groups. The prevalences of anti-B. malayi IgG and IgG4 responses were very similar and much higher than those of microfilaremia or antigenemia. Antibody responses reached the plateau at an earlier age and at a higher prevalence with increased intensity of transmission. For all the markers, the prevalence rates were significantly higher in males than in females.