Embryonic stem cells lacking the epigenetic regulator Cfp1 are hypersensitive to DNA-damaging agents and exhibit decreased Ape1/Ref-1 protein expression and endonuclease activity

Histone methylation can either promote or reduce cellular radiosensitivity by regulating DNA repair pathways

Radiotherapy is one of the primary modalities for cancer treatment, and its efficiency usually relies on cellular radiosensitivity. DNA damage repair is a core content of cellular radiosensitivity, and the primary mechanism of which includes non-homologous end-joining (NHEJ) and homologous recombination (HR). By affecting DNA damage repair, histone methylation regulated by histone methyltransferases (HMTs) and histone demethylases (HDMs) participates in the regulation of cellular radiosensitivity via three mechanisms: (a) recruiting DNA repair-related proteins, (b) regulating the expressions of DNA repair genes, and (c) mediating the dynamic change of chromatin. Interestingly, both aberrantly high and low levels of histone methylation could impede DNA repair processes. Here we reviewed the mechanisms of the dual effects of histone methylation on cell response to radiation. Since some inhibitors of HMTs and HDMs are reported to increase cellular radiosensitivity, understanding their molecular mechanisms may be helpful in developing new drugs for the therapy of radioresistant tumors.

Recent therapeutic strategies for spinal cord injury treatment: possible role of stem cells

Spinal cord injury (SCI) often results in significant dysfunction and disability. A series of treatments have been proposed to prevent and overcome the formation of the glial scar and inhibitory factors to axon regrowth. In the last decade, cell therapy has emerged as a new tool for several diseases of the nervous system. Stem cells act as minipumps providing trophic and immunomodulatory factors to enhance axonal growth, to modulate the environment, and to reduce neuroinflammation. This capability can be boosted by genetical manipulation to deliver trophic molecules. Different types of stem cells have been tested, according to their properties and the therapeutic aims. They differ from each other for origin, developmental stage, stage of differentiation, and fate lineage. Related to this, stem cells differentiating into neurons could be used for cell replacement, even though the feasibility that stem cells after transplantation in the adult lesioned spinal cord can differentiate into neurons, integrate within neural circuits, and emit axons reaching the muscle is quite remote. The timing of cell therapy has been variable, and may be summarized in the acute and chronic phases of disease, when stem cells interact with a completely different environment. Even though further experimental studies are needed to elucidate the mechanisms of action, the therapeutic, and the side effects of cell therapy, several clinical protocols have been tested or are under trial. Here, we report the state-of-the-art of cell therapy in SCI, in terms of feasibility, outcome, and side effects.

Structure and function of active chromatin and DNase I hypersensitive sites

Chromatin is by its very nature a repressive environment which restricts the recruitment of transcription factors and acts as a barrier to polymerases. Therefore the complex process of gene activation must operate at two levels. In the first instance, localized chromatin decondensation and nucleosome displacement is required to make DNA accessible. Second, sequence-specific transcription factors need to recruit chromatin modifiers and remodellers to create a chromatin environment that permits the passage of polymerases. In this review I will discuss the chromatin structural changes that occur at active gene loci and at regulatory elements that exist as DNase I hypersensitive sites.

The epigenetic regulator Cfp1

Numerous epigenetic modifications have been identified and correlated with transcriptionally active euchromatin or repressed heterochromatin and many enzymes responsible for the addition and removal of these marks have been characterized. However, less is known regarding how these enzymes are regulated and targeted to appropriate genomic locations. Mammalian CXXC finger protein 1 is an epigenetic regulator that was originally identified as a protein that binds specifically to any DNA sequence containing an unmethylated CpG dinucleotide. Mouse embryos lacking CXXC finger protein 1 die prior to gastrulation, and embryonic stem cells lacking CXXC finger protein 1 are viable but are unable to achieve cellular differentiation and lineage commitment. CXXC finger protein 1 is a regulator of both cytosine and histone methylation. It physically interacts with DNA methyltransferase 1 and facilitates maintenance cytosine methylation. Rescue studies reveal that CXXC finger protein 1 contains redundant functional domains that are sufficient to support cellular differentiation and proper levels of cytosine methylation. CXXC finger protein 1 is also a component of the Setd1 histone H3-Lys4 methyltransferase complexes and functions to target these enzymes to unmethylated CpG islands. Depletion of CXXC finger protein 1 leads to loss of histone H3-Lys4 tri-methylation at CpG islands and inappropriate drifting of this euchromatin mark into areas of hetero-chromatin. Thus, one function of CXXC finger protein 1 is to serve as an effector protein that interprets cytosine methylation patterns and facilitates crosstalk with histone-modifying enzymes.