CRISPR screens in sister chromatid cohesion defective cells reveal PAXIP1-PAGR1 as regulator of chromatin association of cohesin

The cohesin complex regulates higher order chromosome architecture through maintaining sister chromatid cohesion and folding chromatin by DNA loop extrusion. Impaired cohesin function underlies a heterogeneous group of genetic syndromes and is associated with cancer. Here, we mapped the genetic dependencies of human cell lines defective of cohesion regulators DDX11 and ESCO2. The obtained synthetic lethality networks are strongly enriched for genes involved in DNA replication and mitosis and support the existence of parallel sister chromatid cohesion establishment pathways. Among the hits, we identify the chromatin binding, BRCT-domain containing protein PAXIP1 as a novel cohesin regulator. Depletion of PAXIP1 severely aggravates cohesion defects in ESCO2 mutant cells, leading to mitotic cell death. PAXIP1 promotes global chromatin association of cohesin, independent of DNA replication, a function that cannot be explained by indirect effects of PAXIP1 on transcription or DNA repair. Cohesin regulation by PAXIP1 requires its binding partner PAGR1 and a conserved FDF motif in PAGR1. PAXIP1 co-localizes with cohesin on multiple genomic loci, including active gene promoters and enhancers. Possibly, this newly identified role of PAXIP1-PAGR1 in regulating cohesin occupancy on chromatin is also relevant for previously described functions of PAXIP1 in transcription, immune cell maturation and DNA repair.

Homologous Recombination Deficiency and Cyclin E1 Amplification Are Correlated with Immune Cell Infiltration and Survival in High-Grade Serous Ovarian Cancer

BACKGROUND

How molecular profiles are associated with tumor microenvironment (TME) in high-grade serous ovarian cancer (HGSOC) is incompletely understood. Therefore, we analyzed the TME and molecular profiles of HGSOC and assessed their associations with overall survival (OS).

METHODS

Patients with advanced-stage HGSOC treated in three Dutch hospitals between 2008-2015 were included. Patient data were collected from medical records. BRCA1/2 mutation, BRCA1 promotor methylation analyses, and copy number variations were used to define molecular profiles. Immune cells were assessed with immunohistochemical staining.

RESULTS

348 patients were categorized as BRCA mutation (BRCAm) (BRCAm or promotor methylation) (30%), non-BRCA mutated HRD (19%), Cyclin E1 (CCNE1)-amplification (13%), non-BRCAmut HRD and CCNE1-amplification (double classifier) (20%), and no specific molecular profile (NSMP) (18%). BRCAm showed highest immune cell densities and CCNE1-amplification lowest. BRCAm showed the most favorable OS (52.5 months), compared to non-BRCAmut HRD (41.0 months), CCNE1-amplification (28.0 months), double classifier (27.8 months), and NSMP (35.4 months). Higher immune cell densities showed a favorable OS compared to lower, also within the profiles. CD8+, CD20+, and CD103+ cells remained associated with OS in multivariable analysis.

CONCLUSIONS

Molecular profiles and TME are associated with OS. TME differs per profile, with higher immune cell densities showing a favorable OS, even within the profiles. HGSOC does not reflect one entity but comprises different entities based on molecular profiles and TME.

Setmelanotide, a Novel, Selective Melanocortin Receptor-4 Agonist Exerts Anti-inflammatory Actions in Astrocytes and Promotes an Anti-inflammatory Macrophage Phenotype

To date, available treatment strategies for multiple sclerosis (MS) are ineffective in preventing or reversing progressive neurologic deterioration, creating a high, and unmet medical need. One potential way to fight MS may be by limiting the detrimental effects of reactive astrocytes, a key pathological hallmark for disease progression. One class of compounds that may exert beneficial effects via astrocytes are melanocortin receptor (MCR) agonists. Among the MCR, MC4R is most abundantly expressed in the CNS and several rodent studies have described that MC4R is—besides neurons—expressed by astrocytes. Activation of MC4R in astrocytes has shown to have potent anti-inflammatory as well as neuroprotective effects in vitro, suggesting that this could be a potential target to ameliorate ongoing inflammation, and neurodegeneration in MS. In this study, we set out to investigate human MC4R expression and analyze its downstream effects. We identified MC4R mRNA and protein to be expressed on astrocytes and observed increased astrocytic MC4R expression in active MS lesions. Furthermore, we show that the novel, highly selective MC4R agonist setmelanotide ameliorates the reactive phenotype in astrocytes in vitro and markedly induced interleukin−6 and −11 production, possibly through enhanced cAMP response element-binding protein (CREB) phosphorylation. Notably, stimulation of human macrophages with medium from astrocytes that were exposed to setmelanotide, skewed macrophages toward an anti-inflammatory phenotype. Taken together, these findings suggest that targeting MC4R on astrocytes might be a novel therapeutic strategy to halt inflammation-associated neurodegeneration in MS.

UVB radiation exposes fibrinogen binding sites on platelets by activating protein kinase C via reactive oxygen species

Previous studies have shown that ultraviolet B (UVB) radiation causes platelet aggregation by exposing fibrinogen binding sites via activation of an intracellular mechanism. In the present study we have further investigated the routes of platelet activation following UVB exposure. Evidence is provided that UVB radiation does not activate the platelets via the classical Phospholipase A2 and Phospholipase C routes. Despite this observation, UVB-induced fibrinogen binding was found to be correlated with a 40% increase in phosphorylated 47 kD protein. Both findings could be completely inhibited in the presence of staurosporine, a potent inhibitor of protein kinase C (PK-C). In efforts to explain the mechanism of PK-C activation by UV radiation we found that both UV-induced PK-C activation and platelet aggregation were significantly reduced in the presence of specific scavengers for reactive oxygen species including superoxide dismutase and catalase. We conclude that exposure of platelets to UVB radiation can activate PK-C via oxygen radicals, resulting in exposure of fibrinogen binding sites and subsequent platelet aggregation.

Irradiation of platelets with UV-B light exposes fibrinogen binding sites via an intracellular mechanism

Previous studies have shown that ultraviolet irradiation (UVI) causes platelet aggregation. In the present study we exposed platelet suspensions to a relatively high dose of UV-B (8 J/cm2) under conditions comparable to those of UVI of platelet concentrates in order to obtain more insight into the UV-induced aggregation response and to evaluate the significance of this phenomenon for the clinical use of UV-irradiated platelet concentrates. This study provides evidence that UV-B induced aggregation is mediated by a Ca2(+)-dependent process of fibrinogen binding to an intact glycoprotein IIb-IIIa complex on platelet membranes. Although UV-induced platelet aggregation is independent of thromboxane A2 formation and ADP secretion, it requires metabolic energy, cytosolic Ca2+ and a low cyclic-AMP level. Thus, UV-B irradiation causes platelet aggregation by exposing fibrinogen binding sites via an intracellular mechanism. Since the amount of bound fibrinogen following UVI is relatively low (about 2,300 molecules platelet) and the binding remains reversible, its effect on platelet behaviour after transfusion may be minor.

Evaluation of a new UVB source for irradiation of platelet concentrates

The application of ultraviolet B (UVB) radiation has been proposed as a new technology to decrease immunogenicity of leucocytes in platelet transfusions. UV radiation also induces platelet aggregation, which occurs most effectively at wavelengths between 240 and 280 nm and falls off sharply above 300 nm. In order to minimize the effects of UV energy on the platelets we evaluated in this study the expected benefit of a new narrow-band UVB source, emitting a narrow peak around 312 nm. Exposure of platelet or lymphocyte suspensions to this source induced in the platelets both aggregation and functional defects at a dose of 12 J/cm2 and in the lymphocytes inhibition of in vitro function at a dose of 2 J/cm2. A conventional UVB source, emitting a broad spectrum between 280 and 340 nm, was more deleterious for the cells and induced similar defects in the platelets at a dose of 6 J/cm2 and inhibition of lymphocyte function at a dose of 1 J/cm2. These data indicate no benefit for the new UVB source, since the ratio of the doses to induce platelet defects and inhibition of lymphocyte function is identical for each of the two sources. Absorption of UV energy by plasma and the plastic material of platelet containers is another criterium for selection of UV sources. In view of the better transmission characteristics of long wavelength UV energy we propose that there is a preference for the new narrow-band UVB source.

Filtration. A method to prepare white cell-poor platelet concentrates with optimal preservation of platelet viability

HLA alloimmunization is a major problem for thrombocytopenic patients receiving long-term platelet support. It is caused by white cells (WBCs) that are present as contaminants in platelet concentrates (PCs). Recent data have shown that filtration is an effective means to reduce WBC contamination, but it has little effect on the recovery of platelets. The present report evaluates two filters, a cellulose acetate (CA) filter requiring the inactivation of platelets with prostacyclin and a cotton wool (CW) filter requiring no platelet inactivation. The results show that, using fresh pooled PCs from six random donors, both filters reduce WBC contamination below 10(7) per PC, the likely threshold below which alloimmunization does not develop. With platelets stored for 2 to 3 days the efficacy of the CW filter decreases. Neither filter inflicts important damage to the platelets, as there is no considerable platelet activation or cell disruption. Moreover, PCs prepared by both filters show normal survival and effectively reduce the bleeding times. Thus, filtration of PCs results in platelets with optimal responsiveness both in vitro and in vivo.