Summary Despite of the approval of Photofrin® in various countries, chemically defined sensitizers for photodynamic therapy (PDT) are still needed for the absorption of light in the infrared spectrum, which provides a maximal penetration of light into tissue. Therefore, both the efficacy and the mechanism of action of the clinically approved dye indocyanine green (ICG) and laser irradiation were investigated in vitro. For the investigation of phototoxic effects, HT-29 cells were incubated 24 h prior to irradiation by using different concentrations of ICG (10-500 µM). In each experiment, cells were irradiated using a continuous wave (cw)-diode laser (λ ex = 805 nm, 30 J cm -2 , 40 mW cm -2 ). After laser irradiation, cell viability of dark control and of cells incubated with 500 µM ICG was 1.27 ± 0.11 or 0.28 ± 0.05 respectively. Using 100 µM ICG and D 2 O, cell viability was further decreased from 0.46 ± 0.03 (H 2 O) to 0.11 ± 0.01 (D 2 O). Using D 2 O and 100 µM ICG, the concentration of malondialdehyde, a marker of lipid peroxidation, increased from 0.89 ± 0.10 nmol 10 -6 cells to 11.14 ± 0.11 nmol 10 -6 cells. Using 100 µM ICG and laser irradiation sodium azide or histidine (50 mM), quenchers of singlet oxygen reduced the cell killing significantly. In contrast, when using mannitol, a quencher of superoxide anion and hydroxyl radical, cell killing was not inhibited. According to the present results, photoactivated ICG seems to kill colonic cancer cells due to the generation of singlet oxygen and the subsequent formation of lipid peroxides. Therefore, ICG might present a promising photosensitizer for PDT; first clinical results confirm these findings.

Histone modifications are central to the regulation of all DNA-dependent processes. Lys64 of histone H3 (H3K64) lies within the globular domain at a structurally important position. We identify trimethylation of H3K64 (H3K64me3) as a modification that is enriched at pericentric heterochromatin and associated with repeat sequences and transcriptionally inactive genomic regions. We show that this new mark is dynamic during the two main epigenetic reprogramming events in mammals. In primordial germ cells, H3K64me3 is present at the time of specification, but it disappears transiently during reprogramming. In early mouse embryos, it is inherited exclusively maternally; subsequently, the modification is rapidly removed, suggesting an important role for H3K64me3 turnover in development. Taken together, our findings establish H3K64me3 as a previously uncharacterized histone modification that is preferentially localized to repressive chromatin. We hypothesize that H3K64me3 helps to 'secure' nucleosomes, and perhaps the surrounding chromatin, in an appropriately repressed state during development.

BackgroundThe linker histone H1 has a key role in establishing and maintaining higher order chromatin structure and in regulating gene expression. Mammals express up to 11 different H1 variants, with H1.2 and H1.4 being the predominant ones in most somatic cells. Like core histones, H1 has high levels of covalent modifications; however, the full set of modifications and their biological role are largely unknown.ResultsIn this study, we used a candidate screen to identify enzymes that methylate H1 and to map their corresponding methylation sites. We found that the histone lysine methyltransferases G9a/KMT1C and Glp1/KMT1D methylate H1.2 in vitro and in vivo, and we mapped this novel site to lysine 187 (H1.2K187) in the C-terminus of H1. This H1.2K187 methylation is variant-specific. The main target for methylation by G9a in H1.2, H1.3, H1.5 and H1.0 is in the C-terminus, whereas H1.4 is preferentially methylated at K26 (H1.4K26me) in the N-terminus. We found that the readout of these marks is different; H1.4K26me can recruit HP1, but H1.2K187me cannot. Likewise, JMJD2D/KDM4 only reverses H1.4K26 methylation, clearly distinguishing these two methylation sites. Further, in contrast to C-terminal H1 phosphorylation, H1.2K187 methylation level is steady throughout the cell cycle.ConclusionsWe have characterised a novel methylation site in the C-terminus of H1 that is the target of G9a/Glp1 both in vitro and in vivo. To our knowledge, this is the first demonstration of variant-specific histone methylation by the same methyltransferases, but with differing downstream readers, thereby supporting the hypothesis of H1 variants having specific functions.

Patients with chronic liver disease (CLD) and cirrhosis are at high risk for hepatocellular carcinoma (HCC). Current diagnostic tools for HCC detection include imaging techniques and serum biomarkers such as α-fetoprotein (AFP). Yet, these methods are limited in sensitivity and specificity to accurately detect early HCC. Here we focused on the potential of soluble Axl (sAxl) as a biomarker in CLD patients by analyzing serum samples of 1067 patients and healthy controls from centers in Europe and Asia. We show that serum concentrations of sAxl were significantly increased at early (82.57 ng/mL) and later stages of HCC (114.50 ng/mL) as compared to healthy controls (40.15 ng/mL). Notably, no elevated sAxl levels were detected in patients with CLD including chronic viral hepatitis, autoimmune hepatitis, cholestatic liver disease, or non-alcoholic fatty liver disease versus healthy controls. Furthermore, sAxl did not rise in liver adenomas or cholangiocarcinoma (CCA). Yet, patients with advanced fibrosis (F3) or cirrhosis (F4) showed enhanced sAxl concentrations (F3: 54.67 ng/mL; F4: 94.74 ng/mL). Hepatic myofibroblasts exhibited an increased release of sAxl, suggesting that elevated sAxl levels arise from these cells during fibrosis. Receiver operating characteristic curve analysis of sAxl displayed a strongly increased sensitivity and specificity to detect both cirrhosis (80.8%/92.0%) and HCC (83.3%/86.7%) with an area under the curve of 0.935/0.903 as compared to AFP. In conclusion, sAxl shows high diagnostic accuracy at early stage HCC as well as cirrhosis, thereby outperforming AFP. Importantly, sAxl remains normal in most common CLDs, liver adenomas and CCA.